Radioactivity and X-rays

The discoveries of X-rays and radioactivity were made at the close of the 19th century and became the cornerstones of modern science, leading to a new way of perceiving the structure of the atom and with it a novel type of physics, known as quantum physics, the solution for the age of the Earth, and a revolution in the treatment of cancer. Radioactivity swiftly changed from a study of glowing chemical elements to the nuclear age, at once linking scientific problems with both politics and ethics. The questions of the safety and benefits of radiation and radioactivity have spilled over into the 21st century. Methods of medical diagnosis and treatment of diseases using X-rays and radioactive isotopes are still being perfected, but the events of the previous century have brought about a near-unanimous disapproval of nuclear warfare and at best a sceptical approach to pursuing nuclear power as the main source of energy after fossil fuels. How was radioactivity discovered? How have we benefitted from applications using ionising radiation? And how much is too much?

Radiation invisible to our eyes

In 1857, the French photographer Abel Niépce de Saint Victor noticed that uranium salts made an imprint on photographic paper when left for a long period of time. He published several papers and wrote to the French Academy of Sciences on the strange occurrence, but few took note of the incident at the time. Almost forty years later, the physicist Henri Becquerel repeated the experiment with the aim of finding out whether uranium sulphate could emit X-rays. Wilhelm Conrad Röntgen had discovered X-rays just several months earlier, in 1895, astounding scientists with the idea that rays could travel through black paper, and even visualise bones in a human body. Becquerel had long been interested in the phosphorescence of materials and was hoping to demonstrate that the uranium salt crystals could emit X-rays after being exposed to sunlight. Indeed, the crystals penetrated the black paper, leaving an image on the photographic plates, but bizarrely, this phenomenon also occurred without exposure to sunlight, as Becquerel had left the plates in a drawer for several days. It was the experiment that had rocked the world, as Frederick Soddy explained at the 2nd Lindau Nobel Laureate Meeting in 1952, but for the following two years remained “a curiosity of science”, until Pierre Curie suggested to his new wife Marie that she should study the “Becquerel rays” for her PhD project. The Curies used an electrometer to measure the weak electric current coming from uranium radiation, and these meticulous experiments gave them the advantage of being able to compare the levels of radiation between different samples. They found that thorium was also radioactive, and very shortly afterwards, discovered two new radioactive elements, polonium and radium. Frederick Soddy mentioned these amazing discoveries during his lecture in Lindau in 1952. The Curies’ daughter, Irène Joliot-Curie, herself a Nobel Laureate, was present in the audience:

 

Frederick Soddy (1952) - Isotopes

Now, my lecture is in two parts. A chemical part and a physical part, totally distinct in their methods. And for the physical part I merely am here deputising for the dead. For more than a century since the rise of the modern atomic theory the chemical elements were regarded as homogeneous, the ultimate separate constituents of matter. As propounded by Dalton in the first decade of last century, it was based specifically upon two postulates. The first that the atoms of the same element were the same weight and secondly that the atoms of different elements were of different weights, both of which could hardly have been further from the truth. As the word “isotope” was coined and invented to imitate two Greek words, isos, topos, the same place, and the same place refers to the periodic table of the chemical elements, perhaps it is as well that I should begin by saying something about this periodic law. In the last third of the last century, after the atomic weights of a sufficient number of the elements had been accurately determined, it was found that when they were arranged in order of atomic weight, they fell naturally into families of chemically related or chemically similar elements. And the discoverer of that was Newlands, an Englishman, in 1862 I think. And he knew that a short description of the periodic law could be better than his own words. He said the 8th element in the series is like the first, like the octave of a scale of music. That is the simple law at the beginning and still holds true with a slight modification. It gives you the idea at once, that if you arrange the elements in order of atomic weight, then you will get a number of series of elements. At first it was derided by the chemists, just as isotopes, atomic disintegration and all the rest of it were in my time. But it is well known, its first success was a prediction of the existence of three new elements together with the approximate atomic weights they had and their chemical character. The three, gallium in 1875, scandium in 1879 and germanium in 1887, were predicted by Mendeleev, the Russian chemist, to whom the present form of the periodic table is due. The other great pioneer being Lothar Meyer, a German chemist. Shortly before this, the advent of the spectroscope had revealed four new elements existing in nature in only minute quantity, caesium, rubidium, thallium and indium. Now, these were the elements predicted by Mendeleev. You see at once that by arranging in serial order and from the chemistry of successive columns being alike, you could detect once again, and so Mendeleev was able to predict these three new elements. You notice three points please, this long gap here ... where the rare earth only one which I think is present. These are so alike in their chemistry that they are the nearest example we had formerly to what we now know with isotopes. This slide refers to somewhere around 1890. The slope of the line - it’s difficult for me to see here but you notice the lines on the slope imitating a device of Sir William Crookes - that it really represents not, you see, a split up set of tables but a continuous spiral, wrapped around the cylinder. And that was very important, but that's just this point about it, it was forgotten later, it would have been helpful if they had kept to it. Actually this first family at that time was the alkalines and the last family, the seventh, were the halogens. And you have therefore sudden change from the elements that are most unlike in the whole of those, the table without any intervening gap - I’m referring to 1890. You must forget now about the chemical characters of the periodic table, which before this century was of chief importance, that merely really acted only as a method, as a method by which the elements were arranged in a certain serial order. Roughly but not exactly in order of the atomic weight. And the next point I want you to notice are these two isolating outstanding elements, uranium, thorium, they even then get a great number of elements before you come to this sequence. Continuous without any gaps at all, right through from bismuth to the heavy platinum metals. That’s the second point of importance. I’ll have the next slide, please. Now, this comes to early in the present century. The chief differences you notice with the new, absolutely new family of argon or inert gases discovered in the year 1894 by Lord Rayleigh and Sir William Ramsay. They are, just let these words sink in, without chemical character, they are absolutely inert. And they are the buffers between the strongly electronegative halogens at the extreme right and the strongly electropositive alkali metals at the extreme left. Now also the rare earths have been mainly filled in. They actually here have been taken out of the table. I’m afraid I’m getting mixed with my two slides, would you let me have the next one for a moment, next please … Now, already the discovery of radioactivity in the year 1896 has begun to people this vacant space, between the elements. I have already shown there, even at the beginning of this century the radium emanation, now called radon and Madam Curie’s polonium. Now, this gap is particularly of interest to us, you’d think there was no link whatever between that discovery and radioactivity two years afterwards. There was in fact the most intimate connection for if it hadn’t been for the discovery of those gases in the year 1894 and the subsequent years in the atmosphere, argon only being abundant, the rest being in proportions of millions, beginning with helium, neon, argon, krypton, xenon. Now, a helium exceptionally was found first by Sir Norman Lockyer in the sun by the spectroscope in the year 1868, and then it was traced by Ramsay and Rayleigh to the certain minerals. A certain mineralogist, the American mineralogist Hillebrand had discovered that uraninite, which is the primary mineral of pitchblende, which is a secondary form of it, almost pure oxide of uranium, had a gas which was present in considerable quantity, which he took to be nitrogen. Myles at Oxford told Ramsay about this who at that time was engaged in trying to make argon combine and they separated this gas of Hillebrand’s and it proved to be helium. The solar element, the lightest of that table, and the one that Lockyer had discovered in the solar chromosphere in 1868. Now, I’ll have the next slide please, just for completeness. Now, this is just an up to date version of the present table, we’ve got it out of order somehow where the whole array of lanthanides are now complete ... (inaudible) been taken completely out of the periodic table as a complete exception. This original idea ... (inaudible 14:43), divide them in the first two periods as they are called. After that there’s large numbers of elements are interpolated as shown here from there to there and so on. So that they always increases the number of the order, but that is a probable fairly modern idea dating from maybe 1945 I think, representation of the periodic table as it is today. And it contains practically all the work about which later I shall be speaking. Now, this aroused, of course it doesn’t contain the article, the elements which Professor Hahn has already been speaking. This is extended beyond the uranium, the last one here, six places further on by purely artificial elements. And all the fine gaps that they can place is still there, have been artificially made with the new methods of atomic synthesis which have come in quite within the last decade. Professor Hahn has written a most interesting book on this subject called “The New Atom” which I’d advise you to read. I mustn’t forget to point out that already by this time and before the end of the century it was known that there were exceptions to this rule, this periodic law. No less than three pairs of elements had their atomic weights wrong. They were transposed, the first was tellurium, 127.6, the atomic weight followed by iodine, 126.9, less instead of more and two others, argon followed by potassium, cobalt followed by nickel. So it was well known that the periodic law was not an exact law. Another point at that time that aroused the very keenest interest was the very large proportion of the elements that were integral in atomic weight in terms not of hydrogen - the lowest atomic weight, which is 1.008 - but in terms of oxygen, which is 16. This is far too large a proportion of the whole elements to be due to chance. And it revives a very simple and at first wholly derided hypothesis of Prout in the beginning of the century, immediately following Dalton's atomic theory. Prout, a doctor, had suggested that because of the integral relation of hydrogen and oxygen, which is very nearly, it’s about 1% different really but it was enough in those days. It might be true that the whole of the elements were compounded of hydrogen. And this of course was derided and mathematized by the exact chemists of the day but science had its tragedies as well as its successes. Right up to the very beginning of this century when I was a student, the high water mark of theoretical chemistry was regarded as more and more exact determination of the atomic weights. Under the entirely false impression that they must have some profound physical meaning. ... Right up to the very beginning of this century it was regarded as a high water mark of theoretical chemistry, this exact determination, the atomic weights. Under the false impression that they must have some profound theoretical interest which if you could only grasp would solve the whole cryptogram of the periodic law. Now, 50 years later, it transpires that the work of those original pioneers, beginning with Berzelius, Marignac, Stas, ending with V. W. Morley and T. W. Richards, the last of the American, exact atomic weight chemists, their life work was truly thrown away, as if they’d been engaged in the determination of the specific gravity of a collection of beer bottles, some of them empty, some of them full and some of them partly full and partly empty. And yet, paradoxically enough, the riddle of the periodic table cryptogram is now read so that any child at school can understand it and indeed they ought to be taught it, instead of a lot of the old stuff, in my opinion. The nature of the constitution of matter, in spite of the certain increasing complexity, which has to be put up with, has been enormously simplified of recent years. It was the object of natural philosophy from the very earliest times to find out the nature of the internal constitution of matter. And within the last decade almost that goal has been very largely achieved. And now to my subject, the strange new complexity of matter, which is known by the name of isotope. It was of course a discovery in 1896 by Henri Becquerel of radioactivity, which made inevitable the recognition of this heterogeneity, new heterogeneity in matter. It was established just 50 years ago, almost to a month, and it’s strange that such a jubilee should not have been considered worthy of some formal scientific recognition. For, undoubtedly, it has rocked the world that the two naturally radioactive elements, those isolated pairs at the end of last century, standing alone at the very end of the table, were undergoing a process of spontaneous natural transmutation. The atoms are disintegrating at excessively slow rates, though the actual disintegration of any atom is a sudden, instantaneous or explosive affair. Light particles relatively to the mass of the whole atom are expelled which simulate rays, new atoms are left which correspond to new elements with different properties. In both cases of uranium as for thorium there’s a long series of successive disintegrations in the course of which there comes into existence an infinitesimal quantity for most part, a very large number of new chemical elements, of which radium is typical, of a limited period of life before they proceed to disintegrate again and turn into a new member of a disintegration series. This represents a model of the theories, I won’t go into it very much in detail but the different colours of the various model atoms represent their chemical character. The different colours of the rays that are being expelled, there are only two, white and black, shows the difference in the rays. Now, the important point is this, this is the primary element, uranium or thorium, average period of life lasting thousands of millions of years. This may have a period of a few hours. Indeed the white balls represent the alpha particle, which I have to say, the black balls, the beta particles or the ordinary electron travelling at a speed, near the velocity of light. Only two varieties. These beta rayers, as we call them, are short-lived, relatively. Very rarely, I don’t think any case longer than about quarter of a century. There we come down to the next that may have a life of a million years and so on all the way down. But you’d never know, some of the lives are so short that the existence of a separate member is only in theoretical, you couldn’t possibly distinguish between them. We’re going millions and thousands of millions of a second from the shortest lives. But just remember that the alpha rays are generally more stable than the beta rays. Now, this slide, ... that is the slide that has rocked the world if ever anything has. That’s Becquerel’s first picture of a uranium radiograph, taken by sprinkling or piling over a photographic plate wrapped in black paper a quantity of uranium salt. Putting in between the salt and the film an aluminium medallion and leaving it in a drawer in the dark for weeks. A curious phenomenon, 1896. But followed one year, Roentgen’s famous discovery of the x-rays, known by his name, Roentgen and before him Crookes in England and Lenard in Germany and very many others with the very latest electric appliances of high tension electrical generation, very best high vacuum technique to remove the gas from their vacuum tubes, had discovered x-rays. But this, we had uranium doing of itself and doing more powerfully the very best that at that time could be done by artificial agencies. That was a real wonder of Becquerel’s discovery. It might have remained just a curious, almost curiosity of science, but as is well known for the subsequent work of the Curies. It was Madam Curie, together with a German physicist G. C. Schmidt who discovered the radioactivity of the next element in the table. And that is a radiograph of the ordinary Welsbach mantle which has been, before it burned off, had flattened out, then burned off and laid upon a photographic plate, wrapped up in black paper and left for a few weeks. And you see how the thorium, that’s a positive from the original negative, thorium has imprinted its picture. Now, this is a result of Madam Curie’s very careful systematic analysis of the whole of the known elements of which only one at that time, thorium was radioactive as well as uranium. And then, as everyone knows, that was followed by the dramatic discovery of Madam Curie’s new partially radioactive elements, millions of times more radioactive than uranium and thorium which brought the subject out, being a curiosity to a colossus striding the whole modern world. By Madam Curie’s investigation of the uranium mineral, pitchblende. Now, there’s only one, it’s very important, extremely interesting feature of these amazing discoverers, so well-known, the Curies, for which I have time to mention and I don’t think it’s ever been pointed out before. ... The success of the Curies is simply due to the fact that Madam Curie was a chemist, not a physicist. And instead like Becquerel working with the commercial preparations of uranium after they’ve been treated in the factory, Madam Curie went to the uranium minerals and it was in these minerals that she discovered first polonium and then radium. Now, it’s one of the curiosities of scientific history that no one thought at that time of repeating Madam Curie’s work for uranium with the thorium minerals. And still more curious is it, that when it was done eight years later, it was by reason of an accident instead of it being a conscious piece of research. Now, the essential feature of this discovery or theory of the disintegration of the atom as being the cause of radioactivity is shown for the first change of the radium atom. Now called radon for short, an imitation of argon and the other gases with the same value. It’s been a customary or a privilege to deal with the most amazing changes of matter in the course of their studies, transformations, which were considered for ages magical. But I don’t think any discovery in the old-fashioned molecular chemistry equals in interest or amazing character the first natural transmutation that was made out. You have the sudden explosion, the certain proportion about 1 in 2,500 parts every year of the radium atoms into two different atoms, and these two atoms that are formed turned out to be the lightest and the heaviest of Rayleigh and Ramsay’s argon gases. This disintegration occurs and it was proved very soon afterwards both by Mrs Curie and by ourselves, Rutherford and myself, occurs with the evolution of a million times as much energy as in the most energetic ordinary chemical change known, which results in a helium atom in this case being expelled, the sort of ray, the speed of about 1/15th to 1/20th of that of light itself. There are 14 successive changes in the main series that starts from uranium and ten in that which start from thorium. And in addition there is a minor uranium series starting from the now notorious uranium 235, which formerly, before it was actually known to exist, was called actino-uranium as it was supposed that such an isotope was the parent of the actinium series, which originated like radium from uranium. Can I have now the next slide? These series are set out in detail here, where you have the uranium, a series starting here, the actino-uranium or uranium-235, starting there. The first series starting here, thorium. Broken off with the argon gas family, the emanations as they were first called by Rutherford who discovered them, and then going on right to the very ... (inaudible 32.45) which in each case is shown the nature of the particle that’s expelled, the period of average life in seconds, minutes, hours, centuries and so on, from the beginning to the end. So we come to know in that way some 40 new elements. Almost half as many as were before known. ... When the chemical character of a sufficiently large number of these ephemeral new elements had been made out, then a very strange situation arose which Professor Hahn has already alluded in his earlier lecture. Many of them proved to be completely identical in their chemical nature with one another. Although obviously different being formed from different parents and giving rise to different products. Being distinguished by different rays that have been given out different periods radioactively. And some of them, as we learned later, in the later part of the disintegration series became chemically identical with the elements lead, bismuth and thallium, which are next to the old 1890 periodic table to uranium and thorium at the end of the series. Now, being chemically identical, once mixed they defy separation by chemical analysis. And it was decided novel experience for the chemists to come across simple mixtures, which could not be resolved by chemical means. They could be resolved by physical means, true - theoretically. But as it happens, diffusion, one of the methods of separating gases of different atomic or molecular weight, is one of the most difficult processes to carry out practically. And it wasn’t until the necessity arose for the separation of the two uraniums, for the production of the atomic bomb that it was ever really tackled technologically as a process. Today it remains one of the most marvellously difficult and expensive processes possible to conceive. I coined the word “isotopes” in the year 1913 to signify the same place in the periodic table. But nowadays this could be put much more sweepingly by turning it round. Isotope is by no means confined to the radioactive elements among which it was discovered first. So that one can say that the separate places in the periodic table are occupied more often than not, by a group of different but chemically identical elements that are now called isotopes. Now, in natural radioactivity there are only two ways in which the atom can disintegrate. Why, no one knows, indeed you might say that a great deal about this new subject. ... The theory is merely very often a crude imitation of the facts that conjure up putting into the hat the rabbits that the experimentalist had often pulled out, just before. In both cases the individual atom disintegrating emits a single radiant particle. That had to be assumed at first but was afterwards proved. Like a bullet coming from a gun at a speed a considerable fraction of that of light. And these particles, the alpha, the white ones in my model and the beta, the black ones are different. In the alpha change what are called by Rutherford, their discoverer, alpha particles are expelled, in the beta change electrons. A very penetrating radiation, the beta are penetrating rays like the Roentgen rays, going through opaque matter, only in proportion to the amount in its way, being absorbed only in proportion to the amount in its path. And from the very first they were regarded of course as analogous, never really expected except a much higher velocity to the ordinary cathode rays of the now ubiquitous vacuum tube. That was made out almost as soon as the discovery of radioactivity itself. But the nature of the alpha rays took far longer to establish. For many years they were correctly thought to be atoms of helium as I’ve already indicated, a solar element, which Sir William Ramsay and I proved in 1903, was continually being produced by the element radium. A very first case of a natural transmutation established by ordinary physical and chemical methods. But it wasn’t till about 1911 I think, seven or eight years after their first recognition that Rutherford succeeded in proving with the spectroscope that the alpha rays were veritable helium atoms. Now, though they are much the most important and energetic of the two types, they are very, very feebly penetrating, they are stopped as a rule by a few centimetres of air and corresponding quantity of any other substance. But it’s a miracle that one atom can penetrate another, that is something new if you like. Here we have the second lightest known atom passing clean through all the atoms, 100’s of 1000’s of atoms of the guest in which it passes. And that was pointed out as early as about 1904 by Sir William Bragg in Adelaide, a lone worker right away from all culture, all research. A man, by the way, who had gone out to Australia, not as a physicist but as a mathematician. Who had trained himself in experimental methods entirely alone, isolated, he had most wonderful discovery of this passage of the alpha rays clean through the atoms of matter almost as if they were not there. That’s a case if you like of two particles occupying the same place at the same time. It was upon that property that Rutherford in 1911 to 1913 founded his celebrated nuclear theory of atomic structure. Now, it was the discovery, absolutely simultaneously, 1911 to 1913, of what is now known as the displacement law of radioactive change, that cleared up this whole subject like a flash. For it was then established that when the alpha particle is expelled from the atom, the chemical character of the substance changes in a way to indicate that it has moved in the periodic table, two places nearer the start. When the beta particle is expelled, the change of chemical character is one place in the opposite direction. This is the displacement law of radioactive change, as it appeared in the year 1913 when it was discovered. It was first discovered in the aftermath ... (inaudible 41.39) because they very much longer live than the beta rayers, whereas most of the beta rayers are too short lived to be chemically identifiable. It was my assistant Alexander Fleck of Glasgow, when I’d got hold of the alpha rule of how when an alpha ray is expelled beginning with the thorium series, it jumps two places from the thorium place to the radium place. Dr Hahn’s Thorium-1 (inaudible 42.15). Then it starts to leak in particle one-two. There’s thorium-1 and there’s thorium-2 and it comes back to itself. And then alpha-beta-beta sequenced in any order, which is very common in the radioactive disintegration. And so it comes about, you see, that a matter frequency, that the great grandchild of an element is identical to its parent. It doesn’t have to be order, alpha-beta-beta, it comes back into the same place in the periodic table and is absolutely chemically identical, although four units less in atomic mass, the weight of the alpha particle that has been expelled. It wasn’t until the latter part of the century that it was established of course that this actinium series is derived from a separate isotope of uranium and runs back, that I haven’t time to deal with. Indeed that’s a rather interesting point, that the uranium-235 was only discovered after all the rest of the work had been made out, it was foreshadowed by, what was the man’s name who went up into the stratosphere in a balloon, Piccard, a Swiss investigator, Swiss physicist who went to Belgium. And he called this uranium-235 isotope actino-uranium to indicate that it was a probable bearing to the whole actinium series, which you see there. You might take that just simply, actinium, beta-alpha-alpha-alpha-alpha-beta-alpha-beta. The interesting point about this was that it revealed a half a dozen new things and one of the most important was this: That in every case - that’s the end of the series - and the atomic weight of lead, 207.2, whereas a calculated atomic weight of lead from this one, thorium, is 208, I think, I can hardly see here, this is the lead-208, yes that’s right. The atomic weight of the lead from the uranium series is 206, that from a thorium series is 208 and the common lead is 207. Raising the possibility, you see of ascertaining, proving definitely this theory of isotopy. Because one has only got to go to minerals which contain no thorium, contain uranium only, and separate the lead from them, provided of course that there’s no lead originally in the mineral. And that had become at that time a perfectly well understood technique because it’s a method that enables the geologist to determine the age of the sample, the age of the earth from the amount of lead, the ratio of the lead to the uranium. Whereas at that time the geologists were against even the idea that thorium produced lead too, so they were wrong. I had the good fortune to get from Ceylon a new quantity of a new mineral called thorite, silicate, which was the purest thorium mineral at that time known. It’s not possible to get a mineral like Madam Curie’s pitchblende, uraninite, which contains no thorium to speak of, only the merest trace. But this particular specimen of the thorium mineral contains only very small proportion of uranium. And by hand sorting this most carefully, working up about 30 kilograms of it chemically for the lead, I was able to separate in quantity in the year 1916 thorium lead, the isotope of 208 thorium lead. Whereas T. W. Richards, I’ve already mentioned, the United States atomic weight chemist at that time had similarly tackled pure uranium minerals and determined the age of those which the geologists had selected for him as being suitable in not containing lead originally and had found the atomic weight to be 206. And as to be expected, because even at that time it was expected that the specific gravity of these atoms would be proportional to the atomic weight. The external part of the atom being the same, only the internal part different. We established the specific gravities of these two totally distinct isotopes of lead, separated respectively from thorium and uranium minerals were in agreement with the atomic weight. And that’s the only case where it’s possible to test this theory of isotopy with the ordinary elements, save the one case with the atomic bomb, where after spending 5,000 millions on it they did succeed in separating enough of the uranium-235 by diffusion and other methods from the major isotope 99.3%, 238. And as to be expected, because even at that time it was expected, that the specific gravity of these atoms would be proportional to the atomic weight. The external part of the atom being the same, only the internal part different. We established the specific gravities of these two totally distinct isotopes of lead, separated respectively from thorium and uranium minerals were in agreement with their atomic weight. And that’s the only case where it’s possible to test this theory of isotopy with the ordinary elements. Save the one case with the atomic bomb where after spending 5,000 millions on it, they did succeed in separating enough of the uranium-235 by diffusion and other methods from the major isotope, 99.3%, 238, which Otto Hahn has told you. Just enough for three atomic bombs that exploded respectively at the end of the war on their testing grounds in New Mexico and on two Japanese cities. It is the absolutely most difficult technological feat that’s ever been accomplished by man. It beats to the rare earths, it took years, it took lifetimes of many chemists to separate the rare earths from one another. Each devoting himself to one or two of them. But this is heroic in comparison and it certainly could not have been done, I’m quite certain in any other country but the United States of America under the pressure of war. Now, since the loss of the single negative electron that is the beta particle, sends the atom in the periodic table one place one way, whereas the loss of the doubly positively charged alpha particles sends it two places in the other way. Then it was obvious to the merest tyro that the places in the periodic table represented the internal atomic charge and nothing else. The loss of a negative with the opposite of the loss of two negatives, exact opposite of the loss of one positive alpha particle. And so it came about you see that the cryptogram to a very large extent was read. I should have pointed out the chief change that has come over this modern periodic table compared with all the ones that have been produced before and published without the evidence of radioactive elements that have been discovered and the vacant... (inaudible 51.20). Every place here is numbered, 1 with hydrogen, fairly outside the regular sequence in order 2, 3, 4, 5, up to uranium at the end, only 92. Now, that represented nothing more or less on Rutherford’s nuclear theory than the integral value of the positive charge on the atom’s nucleus. And the periodic table represents nothing but the orderly progressive serial increase from one unit at a time of this nuclear charge. The outside of the atom on this theory is made up of the neutralising electrons, negative electrons, equal in number, individual single electrons equal in number to the positive charge. That is always now called the atomic number. We found that originally only for the limited range at the end of the periodic table from uranium to thallium, the last place is actually entered in that chart that I showed you, but almost immediately the Bohr-Rutherford nuclear theory predicted enabled the positive nuclear charge of the elements to be actually measured. Even before, it was Bragg, the father and son who developed it in this country with the work of Friedrich and Knipping in Austria. Even before that Barkler, one of the Liverpool chemists, physicists in England, had shown that there is a regular increase of penetrating powers of the secondary rays that are produced when you bombard the various elements through the periodic table with high speed Roentgen rays. And this in the hands of Moseley led to his being able definitely to call the roll of the atoms. To say whether or not all were known or whether any vacant places remained. The next slide now, which is think is number nine. That’s his famous, what's called step ladder diagram, showing the regular step wise change in the wavelength of the rays that are produced from the elements in the periodic table. This is calcium, he hadn’t got cadmium you see, so he dropped to the next one, titanium titanium, selenium, chromium, manganese, iron, cobalt, nickel, copper, brass, brass being a mixture of the copper and zinc. This was showing the zinc in addition to the copper line. You see here at a glance, you can tell, anybody could tell that there was a gap here, between this and this. And that was the first picture he got, the x-rays are relatively to the ordinary optical spectre enormously simple, he found only one strong and one weak life. But of course that isn’t when you get up to higher intensities, that isn’t true of the others. And in this way Moseley was able to show the periodic table contained 92 places from hydrogen to uranium. Now, I’m beginning to get into my second part of the subject, the physical part. At this time, 1913, there was one other way of examining an element to see whether it contained isotopes or not, to see whether it was homogeneous or a mixture of different isotopes. And that was a purely physical application of the method by which J. J. Thomson in 1896 had first evaluated the mass, the charge, the velocity of the electron, a negative electron, in 1896. And he’d use it since then, same method, to evaluate the charge of the positive ions. In the electric discharge of gases at very low pressure, which are called positive rays. And these positive rays, which are called anode rays, discovered by Goldstein, had been examined as early 1900 about by a German physicist, Wilhelm Wien I think, who had shown that the mass of the positive is never less than the single hydrogen atom. That was the essence of it. The answer will no doubt will differ according as to whether you’re a philosopher or a practical mind. The isotopes have provided both types of food for thought. To the chemist with a soul of a poet, if there are any such, few discoveries can rival in philosophic interest, the way that isotopes, actually in the language of Keats, swam into our kin. We’ve been honoured with the presence of having listened to Dr. Hahn and I’ve already alluded to the curious circumstance that no one thought of repeating Madam Curie’s epoch-making work for uranium minerals for thorium minerals. As it happens, the very first piece of original work that Professor Hahn did and he’s told you about it and this subject to which he is now our greatest living master in radio chemistry, appeared at first to involve what is now known to be a completely impossible result, the separation of two isotopes, thorium and radiothorium, by simple chemical means. As a research student with Sir William Ramsay he had the good fortune, he told it, to discover a new member of thorium disintegration series. This is the thorium disintegration series. This is the isotope that he discovered, radiothorium. In working out a mineral which was not known to contain thorium, by a simple mistake in the standard German text book of analysis, Fresenius, when the analysis had recorded that mineral, the new mineral from Ceylon, called thorianite, which is not to be confused with thorite, containing a high proportion of uranium but still mainly thorium. It had been imported into England, discovered by the gemmers in Ceylon in their search for jewel, imported into Britain by the Eton college science master named Porter. Sent to Ramsay’s laboratory for analysis and had been returned as mainly zirconium, through an error in Fresenius’s analysis. And had then gone to the factory to be worked up according to Madam Curie’s method. All that Hahn was given by Ramsay was a repetition of Madam Curie’s pioneering work on uranium minerals with a different mineral. And to get practice in separating radium. As it turned out, of course Hahn was given this thing, nobody was consciously, had consciously thought of repeating Madam Curie’s work for the thorium minerals and similar results, it was eight years after the original work of Madam Curie. And the moment he discovered radiothorium which is a body of a considerable period, life of two or three years, the alpha rayer which produces beta rays in the course of time as it disintegrates, all the other chemists, radio chemists in the world tried to do the same thing and failed absolutely. If they could have separated radiothorium, you see, from the ordinary commercial thorium salt, it would have been just as valuable as radium, while it lasted. And it would appear that Hahn had actually done the impossible. But the explanation was given, this is another curious historical point, as early as 1907 by two American chemists, McCoy and Ross, who after trying in vain every known method for purifying thorium, in the attempt to separate the radiothorium that they knew from its radioactivity was there, they had the originality and the courage boldly to state what is a simple adopting of isotope, as early as 1907. Radiothorium and thorianite were in their opinion non-separable by chemical means. So that how did our magician Hahn, a mere tyro at that time, do it? In the meantime, as he told you, he’d crossed the Atlantic, working with Rutherford in Montreal and had come across mesothorium, you see, a new member in the thorium disintegration series. In addition to the radiothorium, (count again two beta-rayers or one, one big beta-... ) ... Now, one position Hahn has done, it seems, is to separate thorium from the radiothorium. ... He discovered the radiothorium, which was not what he’d separated from the mineral which was inseparable, (inaudible 61.30), but his fresh radiothorium he had grown, very difficult to effect the operation. McCoy and Ross correctly pointed out that it was a case of showing what an utterly unanticipated fact really was discovered, inevitably as it would have been, sooner or later, by the fact that the atom is disintegrating. What Hahn has done is to separate mesothorium and thorianite without discovering it. There’s no rays to speak of and this in the course of time had quickly grown a fresh crop of radiothorium, what Hahn had discovered. He had in fact achieved the easy chemical separations of mesothorium from thorium and of radiothorium from mesothorium. The original radiothorium in the mineral remained then as it now is, completely non-separable from the main constituent. How could any more elegant revelation of a tremendous secret, so long and jealously guarded by nature be conceived? By their fruits you shall know them, is true not only of trees as it is of men, but of all unlikely things of the elements and of the atoms. What Hahn and Ramsay working with thorianite were doing like gardeners, trying to separate red tulips from blue, after they had bloomed. The job doesn’t require a gardener at all, as anybody who is doing who is not colour blind, what the other chemists were doing, they were trying to separate it from thorium, to separate before they had bloomed and that no gardener could possibly do. It’s very easy to underrate, looking back, the difficulties that attend even the smallest forward step in discovery, the difficulties of McCoy and Ross which they successfully surmounted in 1907 were so great that I think it deserves recognition. It looks so simple after they discovered the displacement law, but remember that at that time, before that, it was not even known that the product of a radioactive change is, must necessarily be different chemically from its parent. If, as Hahn first thought, radiothorium and thorium were successive in the series, then radiothorium could under no possibility whatever have been discovered. Sometimes as well I think to keep in mind the things that might be, we can’t discover, as to dwell on those that we can. On the practical side, on the other hand, there can be few discoveries in this century likely to prove as great a boom to mankind as that of isotopes. I need do no more than mention this as we are honoured by the presence of the pioneer in this field as you’ve already heard Professor George de Hevesy, who used quite in the early days before the name ‘isotopes’ was coined, used them as tracer elements and later extended it to biological and medical research. That’s about the one and only thing about isotopes that the public probably ever heard. But now that artificial atomic disintegration has been achieved, so that elements have built up at will almost as well as broken down by these new powerful instruments in America that we’ve heard about, it’s possible to make radioactive isotopes of almost all the common elements. Of course, still in completely unweighable amounts, doesn’t matter, because you're not dealing with the weights, you’re dealing with the radioactivity. And there are more radioactive isotopes in the 400 or 500 common isotopes of ordinary elements I already had on the screen. Looking back at the distant days of my youth, before it became possible to break down and build up atoms at will, science then seemed to have been in a preliminary, primitive stage compared with where it is today. Almost one might say it was still at school. Even whatever discoveries there may be in the future, in the science of matter, even though there were none, what we already know now and didn’t know half a century ago will carry man far. One essential condition is that before it’s too late war must be abolished from the earth, let there be no doubt whatever about that, that is the unanimous opinion of every scientific man that has ever expressed an opinion on this burning question. (Applause).

Mein Vortrag gliedert sich in zwei Teile, einen chemischen und einen physikalischen Teil, die von ihren methodischen Ansätzen her völlig unterschiedlich sind. Und was den physikalischen Teil betrifft, vertrete ich hier ausschließlich die Toten, denn seit über einem Jahrhundert und seit dem Aufkommen der modernen Atomtheorie werden die chemischen Elemente als homogene Elemente betrachtet, die letzten isolierbaren Bestandteile von Materie. Wie von Dalton im ersten Jahrzehnt des letzten Jahrhunderts dargelegt, fußte diese Theorie konkret auf zwei Axiomen: Erstens, dass die Atome derselben Elemente dasselbe Gewicht haben, und zweitens, dass die Atome unterschiedlicher Elemente unterschiedliche Gewichte aufweisen, was beides nicht ferner von der Wahrheit entfernt sein könnte. Der Begriff "Isotop" wurde in Anlehnung an zwei griechische Wörter, nämlich "isos" und "topos" - der gleiche Ort - erfunden und geprägt, wobei sich der gleiche Ort auf das Periodensystem der chemischen Elemente bezieht. Vielleicht sollte ich zunächst etwas zu diesem Periodengesetz sagen. Nachdem im letzten Drittel des letzten Jahrhunderts das Atomgewicht einer ausreichenden Zahl von Elementen genau ermittelt worden war, stellte sich heraus, dass bei einer systematischen Anordnung nach ihrem Atomgewicht natürliche Familien von chemisch verwandten oder chemisch ähnlichen Elementen entstehen. Der Entdecker dieser Ordnung war der Engländer Newlands und das war, glaube ich, 1862. Und er wusste, dass eine Kurzbeschreibung dieses Periodengesetzes besser wäre als seine langwierigen Umschreibungen. Er sprach deshalb von einer Anordnung der Elemente in Achtergruppen, wobei das erste Element wie das letzte ist - vergleichbar mit einer Oktave in der Musik. Das ist also gleich zu Beginn das einfache Gesetz, das mit einer kleinen Abänderung noch immer gilt und die zugrunde liegende Vorstellung auf einen Blick vermittelt. Wenn man also die Elemente nach ihren Atomgewichten ordnet, erhält man Reihen von Elementen. Zunächst wurde dieses Konzept von den Chemikern verspottet und verhöhnt - genauso wie Isotope, atomarer Zerfall und all die anderen Dinge in meiner Zeit es wurden. Aber es ist bekannt, dass der erste Erfolg dieses Systems eine Vorhersage der Existenz von drei neuen Elementen mit ihren ungefähren Atomgewichten sowie ihren chemischen Merkmalen war. Die drei, Gallium in 1875, Scandium in 1879 und Germanium in 1887, wurden von dem russischen Chemiker Mendelejew vorhergesagt, auf den die heutige Form des Periodensystems zurückzuführen ist. Der andere große Pionier war Lothar Meyer, ein deutscher Chemiker. Kurz zuvor hatte die Entwicklung des Spektroskops für die Entdeckung von vier neuen Elementen gesorgt, die in der Natur nur in minimalen Mengen vorkommen: Cäsium, Rubidium, Thallium und Indium. Und genau dies waren die von Mendelejew vorausgesagten Elemente. Auf einen Blick sieht man, dass man durch die serielle Anordnung und aus der Ähnlichkeit der Chemie aufeinanderfolgender Spalten neue Elemente entdecken konnte. Und so war Mendelejew in der Lage, diese drei neuen Elemente zu prognostizieren. Achten Sie bitte auf drei Punkte, diese lange Lücke hier ... ich glaube, hier ist nur ein (Element) vorhanden. Diese sind sich chemisch so ähnlich, dass sie von dem, was wir offiziell gefunden hatten, dem am nächsten kamen, was wir heute als Isotope bezeichnen. Dieses Dia bezieht sich auf die Zeit um 1890. Der Anstieg der Linien ... das ist für mich schwer zu sehen ... aber Sie erkennen die ansteigenden Linien, die ein Gerät von Sir William Crookes imitieren, das das hier tatsächlich repräsentiert. Was Sie da sehen, ist nicht ein aufgegliederter Tabellensatz, sondern eine kontinuierliche Spirale rund um den Zylinder. Und das ist sehr wichtig, weil das genau der Punkt ist, der später in Vergessenheit geriet. Es wäre hilfreich gewesen, wenn man sich daran erinnert hätte. Tatsächlich bildeten zu dieser Zeit die Alkalimetalle die erste Familie und die Halogene die letzte, die siebte Familie. Und deshalb gibt es eine sehr plötzliche Veränderung bei den Elementen, die diesen hier in der Tabelle insgesamt sehr unähnlich sind, ohne dass eine Lücke dazwischen liegt, worauf ich 1890 Bezug genommen habe. Vergessen Sie jetzt einmal die chemischen Merkmale des Periodensystems der Elemente, das vor diesem Jahrhundert große Bedeutung hatte und lediglich als Methode dient, nämlich eine Methode, nach der die Elemente in einer bestimmten Reihenfolge angeordnet wurden. Grob, aber nicht exakt in der Reihenfolge ihrer Atomgewichte. Und der nächste Aspekt, auf den ich Sie hinweisen möchte, sind diese beiden getrennten, herausragenden Elemente, Uran, Thorium, und dann hat man eine große Zahl von Elementen, bevor man zu dieser Sequenz kommt. Kontinuierlich ohne Lücken, durchgehend bis (unverständlich 9:49) ... bis zu den schweren Platinmetallen. Das ist der zweite wichtige Punkt. Bitte das nächste Dia. Nun, das hier ist Anfang dieses Jahrhunderts. Die Hauptunterschiede dieser neuen, absolut neuen Familie von Argon- oder inerten Gasen, die im Jahr 1894 von Lord Rayleigh und Sir William Ramsay entdeckt wurden, bestehen darin, dass sie - lassen Sie das einmal auf sich wirken - ohne chemische Merkmale sind. Sie sind absolut inaktiv. Und sie sind die Puffer zwischen den stark elektronegativen Halogenen ganz rechts und den stark elektropositiven Alkalimetallen äußerst links. Inzwischen wurden auch die seltenen Erdelemente größtenteils ergänzt. Tatsächlich wurden sie hier aus dem System herausgenommen. Ich befürchte, dass ich hier zwei Dias verwechselt habe, könnten Sie bitte das nächste Dia zeigen, bitte das nächste ... Mit der Entdeckung der Radioaktivität 1896 begann sich dieser leere Raum hier zwischen den Elementen zu füllen. Ich erwähnte die bereits zur Beginn dieses Jahrhunderts entdeckte Radiumemanation, heute als Radon bezeichnet, sowie das von Madame Curie entdeckte Polonium. Diese Lücke hier ist von besonderem Interesse für uns. Man hätte hier nicht an irgendeine Verbindung zwischen dieser Entdeckung und der Entdeckung der Radioaktivität zwei Jahre später gedacht. In Wirklichkeit aber bestand hier ein sehr starker Zusammenhang, denn sonst wären diese Gase im Jahre 1894 und in den nachfolgenden Jahren nicht in der Atmosphäre entdeckt worden, wobei nur Argon reichlich vorhanden ist und der Rest kommt in millionstel Anteilen vor, beginnend mit Helium, Neon, Argon, Krypton, Xenon. Helium wurde 1868 erstmals von Sir Norman Lockyer mit dem Spektroskop in der Sonne entdeckt, dann wurde es von Ramsay und Rayleigh auf bestimmte Mineralien untersucht. Ein gewisser Mineraloge, der Amerikaner Hillebrand, hatte entdeckt, dass Uraninit, das Primärmineral von Pechblende, was dessen Sekundärform ist, fast reines Uranoxid, in erheblicher Menge ein Gas beinhaltete, das er für Stickstoff hielt. Myles in Oxford erzählte Ramsay darüber, der damals gerade versuchte, Argonverbindungen herzustellen. Und sie separierten dieses Gas von Hillebrand und es erwies sich als Helium, das Sonnenelement, das leichteste im Periodensystem und das, was Lockyer in der Sonnenchromosphäre 1868 entdeckt hatte. Nun möchte ich gerne das nächste Dia zeigen, um die Sache zu vervollständigen ... Dies ist eine aktuelle Version des gegenwärtigen Periodensystems, da ist etwas durcheinander geraten, wo ... das wurde als eine totale Ausnahme komplett aus dem Periodensystem herausgenommen. Diese ursprüngliche Idee ... (unverständlich 14:43) ... die ersten beiden Perioden, wie sie genannt werden. Danach folgt eine riesige Anzahl von Elementen, die hier von da nach da usw. dargestellt sind. Es stimmt, dass sich die Ordnungszahlen erhöht haben, aber das ist, glaube ich, eine ziemlich moderne Idee aus dem Jahr 1945, also die Darstellung des Periodensystems von heute. Und sie enthält praktisch die gesamte Arbeit, über die ich später noch sprechen werde. Nun, hier ist natürlich nicht der Artikel, sind nicht die Elemente berücksichtigt, von denen Professor Hahn bereits gesprochen hat. Das wurde über das Uran hinausgehend um sechs Stellen, um rein künstliche Elemente erweitert. Und all die kleinen Lücken bestehen nach wie vor und sind künstlich mit den neuen Methoden der Atomsynthese erzeugt worden, die im letzten Jahrzehnt entwickelt wurden. Professor Hahn hat ein sehr interessantes Buch zu diesem Thema verfasst mit dem Titel "Das neue Atom", das ich Ihnen sehr empfehlen kann. Ich will nicht vergessen darauf hinzuweisen, dass bereits zum damaligen Zeitpunkt und vor dem Ende des Jahrhunderts Ausnahmen zu dieser Regel, zu diesem Periodengesetz bekannt waren. Nicht weniger als drei Elemente-Paare wiesen falsche Atomgewichte auf. Sie wurden transponiert. Das erste war Tellurium, 127,6 Atomgewicht, gefolgt von Jod mit 126,9, weniger statt mehr, und zwei weitere, Argon gefolgt von Kalium und Kobalt gefolgt von Nickel. Es war also bekannt, dass das Periodengesetz kein exaktes Gesetz war. Ein weiterer Punkt, der zum damaligen Zeitpunkt begeistertes Interesse weckte, war der sehr große Anteil von Elementen, die ein einheitliches Atomgewicht aufwiesen, und zwar nicht in Bezug auf Wasserstoff, dem geringsten Atomgewicht, das bei 1,008 liegt, sondern in Bezug auf Sauerstoff, das bei 16 liegt. Dies ist ein bei weitem zu großer Anteil an den Gesamtelementen, als dass es reiner Zufall sein könnte. Und das rief eine sehr simple und zunächst stark verhöhnte Hypothese in Erinnerung, die Prout zu Beginn des Jahrhunderts direkt nach Daltons Atomtheorie aufgebracht hatte. Prout, ein Arzt, hatte vermutet, dass es aufgrund des integralen Verhältnisses von Wasserstoff und Sauerstoff, das in Wirklichkeit bei rund 1% Unterschied liegt, was aber zur damaligen Zeit ausreichte, stimmen könnte, dass sich alle Elemente aus Wasserstoff zusammensetzen. Und das wurde natürlich verspottet und von den exakten Chemikern der Zeit mathematisiert, aber die Wissenschaft kannte eben sowohl ihre Tragödien als auch ihre Erfolge. Direkt zu Beginn dieses Jahrhunderts, als ich noch Student war, wurde die stets exaktere Ermittlung der Atomgewichte als das Höchste der theoretischen Chemie betrachtet. Unter völlig falschen Eindruck, dass sie von grundlegender physikalischer Bedeutung sind ... Direkt zu Beginn dieses Jahrhunderts wurde diese exakte Ermittlung der Atomgewichte als das absolut Höchste in der theoretischen Chemie betrachtet - unter dem falschen Eindruck, dass sie von grundlegendem theoretischen Interesse seien und, wenn man sie nur erfassen würde, das gesamte Kryptogramm des Periodengesetzes aufklären könnten. Heute, 50 Jahre später, stellt sich heraus, dass die Arbeit von Pionieren wie Berzelius, Marignac, Stas und schließlich V. W. Morley und T. W. Richards, den letzten amerikanischen Chemikern, die sich mit dem exakten Atomgewicht beschäftigt haben, also dass ihr Lebenswerk in Wirklichkeit weggeworfen wurde, als hätten sie sich mit der Ermittlung des spezifischen Gewichts einer Sammlung von Bierflaschen beschäftigt, von denen einige leer, andere wiederum voll und einige halb voll und halb leer gewesen sind. Und paradoxerweise lässt sich das Kryptogrammrätsel des Periodensystems heute so lesen, dass jedes Kind in der Schule es verstehen kann und die Schüler das auch meiner Ansicht nach anstelle all des anderen alten Zeugs lernen sollten. Die Natur der Beschaffenheit der Materie konnte trotz der gewiss vorhandenen, zunehmenden Komplexität, mit der man zu tun hat, in den letzten Jahren enorm vereinfacht werden. Die Naturphilosophie hat sich bereits in früher Zeit damit beschäftigt, die Natur der inneren Beschaffenheit der Materie aufzuklären. Und innerhalb des letzten Jahrzehnts ist dieses Ziel größtenteils erreicht worden. Und nun zu meinem Thema, der seltsamen neuen Komplexität von Materie, die unter dem Begriff "Isotope" bekannt ist. Es war eine Entdeckung im Jahre 1896, nämlich die Entdeckung der Radioaktivität durch Henri Becquerel, die zwangsläufig zur Entdeckung dieser Heterogenität, dieser neuen Heterogenität in Materie führte. Das ist jetzt - fast auf einen Monat genau - 50 Jahre her, und es ist doch seltsam, dass man sich angesichts eines solchen Jubiläums keine offizielle wissenschaftliche Form der Anerkennung überlegt hat. Denn diese Entdeckung hat doch zweifelsohne die Welt ins Wanken gebracht, dass die beiden natürlichen radioaktiven Elemente, diese isolierten Paare, die am Ende des letzten Jahrhunderts allein am absoluten Ende des Periodensystems standen, einen Prozess der natürlichen Transmutation durchliefen. Die Atome zerfallen bei extrem langsamer Geschwindigkeit, während der eigentliche Zerfall eines Atoms eine plötzliche, augenblickliche oder explosive Angelegenheit ist. Im Verhältnis zur Masse des Gesamtatoms leichte Teilchen werden ausgestoßen und simulieren Strahlen. Zurück bleiben neue Atome, die neuen Elementen mit anderen Merkmalen entsprechen. Sowohl bei Uran als auch bei Thorium gibt es eine lange Kette von aufeinander folgenden Zerfallsprozessen, in deren Verlauf eine riesige Zahl neuer chemischer Elemente, größtenteils in unendlich kleiner Menge, entsteht, für die Radium typisch ist. Diese haben nur einen begrenzten Lebenszeitraum, bevor sie ihren Zerfallsprozess fortsetzen und sich in ein neues Element einer Zerfallsreihe verwandeln. Das hier ist die Darstellung eines Modells der Theorien. Ich möchte darauf nicht näher eingehen, aber die verschiedenen Farben der verschiedenen Modellatome repräsentieren ihren chemischen Charakter. Die unterschiedlichen Farben der ausgestoßenen Strahlen - das sind nur zwei, nämlich weiß und schwarz - stehen für die Verschiedenheit der Strahlen. Wichtig ist hier, dass das hier das Primärelement ist, Uran oder Thorium, mit einer durchschnittlichen Lebensdauer von Tausenden von Millionen Jahren. Das hier hat möglicherweise eine Lebensdauer von einigen wenigen Stunden. Die weißen Kugeln repräsentieren die Alpha-Teilchen, auf die ich noch eingehen werde, die schwarzen Kugeln die Beta-Teilchen oder das gewöhnliche Elektron, das sich fast in Lichtgeschwindigkeit bewegt. Nur zwei Varianten. Diese Beta-Strahlen, wie wir sie nennen, sind relativ kurzlebig. Sehr bald, ich glaube, auf keinen Fall länger als ungefähr ein Vierteljahrhundert. Dann kommen wir zu den nächsten, die eine potenzielle Lebensdauer von einer Million Jahre haben usw., bis ganz nach unten. Aber man kann nie wissen. Einige Leben sind so kurz, dass nur theoretisch ein separates Element existiert. Man könnte diese Elemente nicht einmal voneinander unterscheiden. Bei den kürzesten Lebensdauern reden wir über ein Millionstel und Tausendmillionenstel einer Sekunde. Aber ich möchte Sie daran erinnern, dass die Alpha-Strahlen grundsätzlich stabiler sind als die Beta-Strahlen. Nun, dieses Dia ... das ist das Dia, das die Welt ins Wanken gebracht hat, wie kaum ein anderes. Das ist das erste Bild Becquerels von einem Uran-Röntgenbild. Dazu wurde über eine fotografische Platte, die in schwarzes Papier eingehüllt war, Uransalz gestreut und dann zwischen das Salz und den Film ein Aluminiummedaillon platziert. Das Ganze wurde dann wochenlang abgedunkelt in einem Schubfach gelagert. Ein seltsames Phänomen, 1896. Ein Jahr später folgte Röntgens berühmte Entdeckung der Röntgenstrahlen, die seinen Namen berühmt gemacht haben. Vor ihm hatten bereits Crookes in England und Lenard in Deutschland und viele andere mit den neuesten elektrischen Geräten zur Erzeugung von Hochspannung und Stromerzeugung und dieser hochwertigen Vakuumtechnik, mit der sich das Gas aus den Vakuumröhren entfernen ließ, die Röntgenstrahlen entdeckt. Aber dieses erledigte Uran wesentlich leistungsstärker und besser als durch künstlich geschaffene Einrichtungen. Das war das eigentliche Wunder der Entdeckung von Becquerel. Es hätte einfach ein Kuriosum, ein Kuriosum der Wissenschaft bleiben können, aber bekanntlich wurde es durch die nachfolgenden Arbeiten der Curies berühmt. Es war Madame Curie, die gemeinsam mit einem deutschen Physiker namens G. C. Schmidt die Radioaktivität des nächsten Elements im Periodensystem entdeckte. Und das ist eine Röntgenaufnahme des normalen Welsbach-Glühstrumpfes, der sich vor dem Abbrennen verflacht hatte, dann abgebrannt ist und auf eine fotografische Platte gelegt wurde, in schwarzes Papier gehüllt und einige Wochen ruhte. Und sie sehen, wie sich Thorium (das ist ein Positiv des ursprünglichen Negativs) auf dem Bild eingeprägt hat. Diese Arbeit ist das Ergebnis von Madame Curies sehr sorgfältiger systematischer Analyse aller bekannten Elemente, von denen zum damaligen Zeitpunkt nur eines, nämlich Thorium, ebenso wie Uran radioaktiv war. Und dann folgte, wie jeder weiß, Madame Curies dramatische Entdeckung von neuen teilradioaktiven Elementen, millionenfach radioaktiver als Uran und Thorium, die das Thema, das bisher als unwichtig galt, zu einem Riesenthema für die gesamte moderne Welt machten - durch Madams Curies Untersuchung des Uranminerals Pechblende. Nun, es gibt eine sehr bedeutende, extrem interessante Besonderheit an den Entdeckungen dieser bekannten Curies, die ich hier noch erwähnen möchte. Ich glaube, darauf ist noch nie hingewiesen worden ... Der Erfolg der Curies ist schlicht und einfach auf die Tatsache zurückzuführen, dass Madame Curie Chemikerin war und nicht Physikerin. Und statt wie Becquerel mit den kommerziellen Präparaten von Uran zu arbeiten, die in der Fabrik behandelt worden sind, griff Madame Curie auf die Uranmineralien zurück. Und genau in diesen Mineralien fand sie erstmalig Polonium und dann Radium. Es gehört zu den Kuriositäten der Wissenschaftsgeschichte, dass zum damaligen Zeitpunkt niemand daran glaubte, dass Madame Curies Arbeit über Uran mit den Thorium-Mineralien wiederholt werden könnte. Und noch kurioser ist die Tatsache, dass dies, als es acht Jahre später erfolgte, aufgrund eines Zufalls und nicht durch gezielte Forschungsarbeiten geschah. Die wesentliche Besonderheit dieser Entdeckung oder Theorie vom Atomzerfall als Ursache der Radioaktivität ist an der ersten Umwandlung des Radiumatoms festzumachen. Heute wird es verkürzt als Radon bezeichnet, eine Imitation von Argon und den anderen Gasen mit demselben Wert. Es ist üblich bzw. ein Privileg, dass man im Laufe seiner Untersuchungen mit den erstaunlichsten Veränderungen von Materie zu tun bekommt, Transformationen, die als magisch bezeichnet werden können. Aber ich kenne keine Entdeckung in der altmodischen Molekularchemie, die genauso interessant oder erstaunlich ist wie die erste Transmutation, die entdeckt wurde. Es gibt diese plötzliche Explosion, dieses Verhältnis von rund 1:2.500 Teilchen pro Jahr der Radiumatome in zwei unterschiedliche Atome. Und bei diesen beiden Atomen handelt es sich um die leichtesten und schwersten Argongase von Rayleigh und Ramsay. Dieser Zerfall geschieht - und das wurde sehr kurz darauf sowohl von Madame Curie als auch von uns, Rutherford und mir, nachgewiesen - mit der Entwicklung einer millionenfachen Energie der energievollsten normalen chemischen Veränderungen, die bekannt sind, sodass in diesem Fall ein Heliumatom in Form eines Strahls mit einer Geschwindigkeit von 1/15 bis 1/20 der Lichtgeschwindigkeit ausgestoßen wird. Es gibt 14 aufeinander folgende Veränderungen in der Hauptreihe, die mit Uran beginnt, und zehn in der mit Thorium beginnenden Reihe. Und zusätzlich gibt es eine kleinere Uran-Reihe, die mit dem heute bekannten Uran 235 beginnt, das, bevor seine Existenz tatsächlich bekannt war, als Actinium-Uran bezeichnet wurde, da angenommen wurde, dass ein solches Isotop das Mutterelement der Actinium-Reihe ist, das wie Radium aus Uran hervorgeht. Kann ich bitte das nächste Dia haben? Diese Reihen werden hier detailliert dargelegt, hier ist das Uran, eine Reihe startet hier, das Actinium-Uran oder Uran 235 beginnt hier. Die erste Reihe beginnt hier, Thorium. Unterbrochen durch die Argon-Gasfamilie, die Emanationen, wie Rutherford sie zuerst genannt hat, der sie entdeckt hatte, und das geht dann hier rechts weiter ... (unverständlich 32:45), wobei jeweils die Beschaffenheit des Teilchens, das ausgestoßen wird, und die durchschnittliche Lebensdauer in Sekunden, Minuten, Stunden, Jahrhunderten usw. vom Anfang bis zum Ende angezeigt wird. Auf diese Weise lernten wir rund 40 neue Elemente kennen. Nicht weniger als fast die Hälfte der Anzahl, die bereits vorher bekannt war ... Als die chemischen Merkmale einer ausreichend großen Zahl dieser kurzlebigen neuen Elemente bekannt waren, ergab sich eine sehr merkwürdige Situation, die Professor Hahn bereits in seinem früheren Vortrag beschrieben hat. Viele dieser Elemente stellten sich in ihrer chemischen Beschaffenheit als untereinander komplett identisch heraus, obwohl sie offensichtlich aus unterschiedlichen Elternelementen gebildet wurden und Anlass zu unterschiedlichen Produkten gegeben hatten sowie auch durch unterschiedliche Strahlen unterscheidbar waren, die unterschiedlich lange radioaktiv wirkten. Und wie wir später erfuhren, erreichten einige davon im letzten Teil der Abbaureihen chemische Identität mit den Elementen Blei, Wismut und Thallium, die im alten Periodensystem von 1890 neben Uran und Thorium am Ende der Reihe standen. Obwohl chemisch identisch, widersetzen sie sich nach ihrer Vermischung einer Isolierung durch chemische Analyse. Und es war eine ganz und gar neue Erfahrung für die Chemiker, einfache Verbindungen vor sich zu haben, die sie nicht mit chemischen Mitteln trennen konnten. Sie konnten mit physikalischen Mitteln aufgelöst werden, aber nur theoretisch. Denn die Diffusion, eine der Methoden zur Trennung von Gasen mit unterschiedlichen Atom- oder Molekülgewichten, zählt in der Praxis zu den am schwierigsten durchzuführenden Verfahren. Und erst, als zwecks Herstellung der Atombombe die Notwendigkeit zur Trennung der beiden Uran-Elemente bestand, wurde dieser technische Prozess tatsächlich in Angriff genommen. Auch heute noch ist das eines der wirklich schwierigsten und teuersten Verfahren, die man sich überhaupt vorstellen kann. Ich habe das Wort "Isotope" im Jahr 1913 geprägt, um denselben Platz im Periodensystem anzudeuten. Heutzutage könnte dieses Wort aber umfassender im umgekehrten Sinn verstanden werden. Isotope beschränken sich auf keinen Fall auf die radioaktiven Elemente, bei denen sie zuerst festgestellt wurden. Man kann also sagen, dass die separaten Stellen im Periodensystem öfter als nicht von einer Gruppe von unterschiedlichen, aber chemisch identischen Elementen belegt werden, die heute als Isotope bezeichnet werden. Bei der natürlichen Radioaktivität gibt es nur zwei Möglichkeiten für den Atomzerfall. Warum das so ist, weiß niemand. Tatsächlich könnte man sagen, dass viel zu diesem neuen Thema ... Die Theorie ist sehr oft nur eine grobe Imitation der Fakten, die heraufbeschworen werden, wenn man die Kaninchen, die der Experimentalphysiker erst kurz zuvor aus dem Hut gezaubert hat, wieder in den Hut hineinsteckt. In beiden Fällen gibt das einzelne zerfallende Atom ein einzelnes Strahlungsteilchen ab. Davon ging man zunächst aus, aber es hat sich auch im Nachhinein bestätigt. Wie eine Kugel, die aus einem Gewehrlauf herausschießt - und zwar in einer Geschwindigkeit, die einem erheblichen Bruchteil der Lichtgeschwindigkeit entspricht. Und diese Teilchen, die Alpha-Teilchen, die weißen in meinem Modell, und die Beta-Teilchen, die schwarzen, sind unterschiedlich. Bei der Alpha-Veränderung werden die von ihrem Entdecker Rutherford als Alpha-Teilchen bezeichneten Teilchen ausgestoßen, bei der Beta-Veränderung Elektronen. Die Beta-Strahlen sind wie die Röntgenstrahlen sehr durchdringende Strahlen, die opake Materie durchdringen und nur im Verhältnis zu der ihnen im Wege stehenden Menge absorbiert werden. Und von Anfang an wurden sie natürlich als analog betrachtet, niemals ... (unverständlich 37:47), mit Ausnahme der wesentlich höheren Geschwindigkeit gegenüber den normalen Kathodenstrahlen der heute überall verbreiteten Vakuumröhre, die fast genauso schnell herausgefunden wurde wie die Entdeckung der Radioaktivität selbst. Aber es sollte wesentlich länger dauern, die Beschaffenheit der Alpha-Strahlen zu ermitteln. Viele Jahre hielt man sie richtigerweise für Helium-Atome, wie ich bereits andeutete, ein Sonnenelement, das, wie Sir William Ramsay und ich 1903 nachwiesen, kontinuierlich vom Element Radium erzeugt wird. Der allererste Fall einer natürlichen Transmutation wurde durch einfache physikalische und chemischen Methoden bestätigt. Aber erst um 1911, sieben oder acht Jahre nach der ersten Entdeckung, gelang Rutherford mit dem Spektroskop der Nachweis, dass die Alpha-Strahlen in Wahrheit Helium-Atome waren. Obwohl sie die wichtigsten und energiereichsten der beiden Arten sind, sind sie nur sehr, sehr schwach durchdringend. Sie werden in der Regel von wenigen Zentimetern Luft und einer entsprechenden Menge anderer Substanzen aufgehalten. Aber es ist ein Wunder, dass ein Atom ein anderes durchdringen kann. Das ist etwas Neues, wenn man so will. Hier sehen Sie das zweitleichteste bekannte Atom, das unbeschränkt alle Atome durchquert, Hunderttausende von Atomen des Gastes, den es durchquert. Und das wurde bereits 1904 von Sir William Bragg in Adelaide festgestellt, einem einsamen Forscher fern von jeder Kultur, jeder Forschung. Einem Mann übrigens, der nicht als Physiker, sondern als Mathematiker nach Australien gegangen war. Der sich völlig selbstständig in experimentelle Verfahren eingearbeitet hatte und völlig isoliert war. Er entdeckte diese wunderbare unbeschränkte Durchquerung der Alphastrahlen, die die Atome von Materie unbeschränkt durchqueren, als ob sie gar nicht da wären. Wenn so man will, ist das ein Fall von zwei Teilchen, die dieselbe Stelle gleichzeitig besetzen. Und genau auf diese Eigenschaft fußte Rutherford 1911 bis 1913 seine gefeierte Kerntheorie der Atomstruktur. Es war die 1911 bis 1913 zeitlich absolut simultan erfolgte Entdeckung dessen, was heute als das Verschiebungsgesetz der radioaktiven Umwandlung bekannt ist, was diese gesamte Thematik schlagartig aufklärte. Denn es zeigte sich, dass sich der chemische Charakter der Substanz bei Abstoßung des Alpha-Teilchens vom Atom so ändert, dass es im Periodensystem um zwei Einheiten weiter nach vorne rückt. Wenn das Beta-Teilchen ausgestoßen wird, ändert sich die chemische Beschaffenheit um eine Ordnungszahl in die entgegengesetzte Richtung. Dies ist das Verschiebungsgesetz der radioaktiven Umwandlung, das 1913 entdeckt wurde. Es wurde erstmalig entdeckt infolge ... (unverständlich 41:39) ... ein sehr viel längeres Leben als die Beta-Strahlen, wobei die meisten Beta-Strahlen zu kurzlebig sind, als dass man sie chemisch identifizieren könnte. Es war mein Assistent Alexander Fleck aus Glasgow, als ich die Alpha-Regel dazu erkannte, wie die Thorium-Reihe, wenn ein Alpha-Strahl ausgestoßen wird, zwei Plätze von der Thorium-Stelle zur Radium-Stelle springt ... (unverständlich 42:15). Es gibt Thorium-1 und Thorium-2 und das kehrt zu sich selbst zurück. Und dann Alpha-Beta-Beta-Sequenzen in beliebiger Reihenfolge, was beim radioaktiven Zerfall sehr häufig vorkommt. Und so kommt es, wie Sie sehen, dass eine Materienfrequenz, dass der Urenkel eines Elements identisch ist mit seinem ... (unverständlich 42:50). Es muss nicht in der Reihenfolge Alpha-Beta-Beta sein, es kehrt an die gleiche Stelle im Periodensystem zurück und ist chemisch absolut identisch, wenn auch vier Einheiten weniger in der Atommasse, dem Gewicht des ausgestoßenen Alpha-Teilchens. Erst Ende des Jahrhunderts wurde festgestellt, dass diese Actinium-Reihe von einem separaten Uran-Isotop abgeleitet ist und rückwärts läuft, worauf ich hier aus zeitlichen Gründen nicht eingehen kann. Ziemlich interessant ist der Aspekt, dass das Uran 235 erst entdeckt wurde, nachdem alle anderen Arbeiten ausgeführt worden waren. Angedeutet hatte das schon dieser Mann, wie hieß er auch wieder, der sich mit einem Ballon in die Stratosphäre begab, Piccard, ein Schweizer Erfinder, ein Schweizer Physiker, der nach Belgien ging. Und er nannte dieses Uran-235-Isotop Actinium-Uran, um den wahrscheinlichen Bezug zur gesamten Actinium-Reihe anzugeben, die man hier sieht. Man kann das so einfach betrachten, Actinium, Beta-Alpha-Alpha-Alpha-Alpha-Beta-Alpha-Beta. Interessant daran war, dass dadurch ein halbes Dutzend neuer Dinge entdeckt wurde und eines der wichtigsten war das Folgende: Dass das in jedem Fall das Ende der Reihe ist, das Atomgewicht von Blei, 207,2, während das kalkulierte Atomgewicht von Blei von diesem hier, Thorium, 208 ist, glaube ich, ich kann das hier kaum erkennen, da ist das Blei 208, ja, das ist richtig. Das Atomgewicht von Blei aus der Uran-Reihe ist 206, das von einer Thorium-Reihe ist 208 und das übliche Blei ist 207. Damit entstand die Möglichkeit, diese Isotopentheorie zu bestätigen und definitiv nachzuweisen. Denn man braucht nur Mineralien zu nehmen, die kein Thorium enthalten, sondern nur Uran enthalten und das Blei separieren, vorausgesetzt, natürlich, dass sich in dem Mineral ursprünglich kein Blei befindet. Und das war zur damaligen Zeit bereits eine perfekte und gut untersuchte Technik, weil Geologen mit dieser Methode das Alter der Probe, das Alter der Erde aus der Menge des Bleis, dem Verhältnis des Bleis zum Uran, ermitteln können. Zur damaligen Zeit konnten sich die Geologen absolut nicht vorstellen, dass Thorium auch Blei erzeugt. Da lagen sie falsch. Ich hatte das Glück, aus Ceylon eine gewisse Menge eines Minerals mit der Bezeichnung Thorit, ein Silikat, zu erhalten, das zum damaligen Zeitpunkt das reinste bekannte Thorium-Mineral war. Es war nicht möglich, ein Mineral wie Madame Curies Pechblende, Uranimit, zu erhalten, das kein Thorium in bemerkenswerter Menge enthält, nur kleinste Spuren. Aber diese spezielle Probe des Thorium-Minerals enthält nur einen sehr kleinen Anteil Uran. Und durch eine sehr sorgfältige manuelle Aufbereitung von über 30 kg auf der Suche nach Blei konnte ich 1916 eine gewisse Menge von Thorium-Blei separieren, das Isotop von 208-Thorium-Blei. Der von mir bereits erwähnte T. W. Richards, US-amerikanischer Atomgewichtschemiker, hatte damals in ähnlicher Weise reine Uranmineralien untersucht und das Alter von Mineralien bestimmt, die Geologen für ihn ausgewählt hatten, weil sie kein Blei enthielten. Und für diese hatte er ein Atomgewicht von 206 ermittelt. Und wie zu erwarten war, weil man damals schon davon ausging, dass das spezifische Gewicht dieser Atome proportional zum Atomgewicht und der externe Teil des Atoms gleich und nur der innere Teil unterschiedlich ist, ermittelten wir die spezifischen Gewichte dieser beiden völlig unterschiedlichen Blei-Isotope, die von Thorium- und Uranmineralien isoliert worden waren, in Übereinstimmung mit dem Atomgewicht. Und das ist der einzige Fall, wo es möglich war, diese Isotopen-Theorie mit den einfachen Elementen zu überprüfen - mit der einzigen Ausnahme der Atombombe, wo man nach Investition von 5.000 Millionen in der Lage war, durch Diffusion und andere Methoden genug Uran 235 vom Hauptisotop 99,3%, 238, zu separieren, worüber Otto Hahn ja bereits berichtet hat. Gerade genug für die drei Atombomben, die bei Kriegsende auf dem Testgelände in New Mexico und über zwei japanischen Städten explodierten. Es ist wohl das komplexeste technologische Meisterstück, das jemals von Menschen erreicht wurde. Es schlägt die seltenen Erdmetalle. Es brauchte Jahre, es brauchte die Lebenszeit vieler Chemiker, die seltenen Erdmetalle voneinander zu trennen, wobei sich jeder auf ein oder zwei beschränkt hat. Aber dies ist im Vergleich dazu eine Heldentat und sie wäre, da bin ich ziemlich sicher, in keinem anderen Land möglich gewesen als unter dem Druck des Krieges in den Vereinigten Staaten von Amerika. Weil der Verlust des einzelnen negativen Elektrons, bei dem es sich um das Beta-Teilchen handelt, das Atom im Periodensystem um eine Stelle in eine Richtung verschiebt, während der Verlust der doppelt positiv geladenen Alpha-Teilchen es zwei Stellen in die andere Richtung verschiebt, war selbst für den reinsten Anfänger erkennbar, dass die Stellen im Periodensystem nichts anderes als die innere Atomladung repräsentierten. Der Verlust eines negativen Teilchens mit dem Gegenteil des Verlustes von zwei negativen Teilchen, das genaue Gegenteil zum Verlust eines positiven Alphateilchens. Und so kam es dazu, dass das Kryptogramm weitgehend lesbar wurde. Ich möchte noch auf die wesentliche Veränderung eingehen, die für dieses moderne Periodensystem eingeführt wurde, im Vergleich zu all den wunderbaren ... (unverständlich 51:20). Jede Stelle wurde mit einer Ordnungszahl versehen, 1 für Wasserstoff, ziemlich außerhalb der regulären Reihenfolge, 2, 3, 4, 5 bis hin zum Uran am Schluss, erst 92. Das repräsentierte in der Kerntheorie von Rutherford nicht mehr und nicht weniger als den Integralwert der positiven Atomkernladung. Und das Periodensystem ist nichts anderes als die Darstellung der systematischen, fortschreitenden, seriellen Zunahme ... (unverständlich 51:58) dieser Kernladung. Bei dieser Theorie besteht das Atomäußere aus den neutralisierenden Elektronen, negativen Elektronen, in gleicher Anzahl, individuellen Einzelelektronen, die in ihrer Anzahl der positiven Ladung entsprechen. Das wird heute einheitlich als Atomzahl bezeichnet. Wir haben das ursprünglich nur für das begrenzte Spektrum am Ende des Periodensystems von Uran bis Thallium festgestellt. Die letzte Stelle wurde tatsächlich in dieses Diagramm, das ich Ihnen gezeigt habe, eingetragen. Aber praktisch sofort wurde mit der Kerntheorie von Bohr-Rutherford vorausgesagt ... Nein, ich fürchte, ich irre mich, es war nicht die Bohr-Rutherford-Theorie. Es war das Aufkommen der Röntgenspektroskopie, das die tatsächliche Messung der positiven Kernladung der Elemente ermöglichte. Schon früher hatten Vater und Sohn Bragg diese Technik in diesem Land mit Hilfe der Arbeiten von Friedrich und Knipping in Österreich entwickelt. Bereits vorher hatte Barkler, einer der Liverpooler Chemiker, Physiker in England, nachgewiesen, dass die Durchdringungskräfte von Sekundärstrahlen, die bei Bombardierung verschiedener Elemente des Periodensystems mit Hochgeschwindigkeitsröntgenstrahlen entstehen, gleichmäßig ansteigen. Und dies führte dazu, dass Moseley die Funktion der Atome definitiv aufklären konnte, also, ob alle bekannt waren oder ob freie Stellen blieben oder nicht. Das nächste Dia bitte, das müsste die Nummer 9 sein. Das ist sein berühmtes, so genanntes Leiterdiagramm, das die gleichmäßige, stufenweise Veränderung der Wellenlänge der von den Elementen im Periodensystem erzeugten Strahlen angibt. Das hier ist Calcium, das Kadmium hatte er noch nicht, wie Sie sehen. Deshalb sprang er zum nächsten, Titan, Selen, Chrom, Mangan, Eisen, Kobalt, Nickel, Kupfer, Messing, wobei Messing eine Mischung aus Kupfer und Zink ist. Das heißt also, dass Zink zusätzlich zum Kupfer vorhanden ist. Man sieht hier auf einen Blick, dass man das zählen kann. Jeder könnte das zählen und herausfinden, dass hier zwischen diesen beiden Elementen eine Lücke ist. Und das war der erste Eindruck, den er hatte, dass die Röntgenstrahlen im Verhältnis zum gewöhnlichen optischen Spektrum enorm einfach sind, er fand nur ein starkes und ein schwaches Leben. Das gilt natürlich nicht für all die anderen, wenn man zu den höheren Intensitäten geht. Und so konnte Moseley nachweisen, dass das Periodensystem vom Wasserstoff bis zum Uran aus 92 Stellen besteht. Ich komme jetzt zu meinem zweiten Teil des Themas, dem physikalischen Teil. Zum damaligen Zeitpunkt, 1913, gab es nur eine Möglichkeit festzustellen, ob ein Element Isotope enthielt oder nicht, ob es homogen war oder eine Mischung aus verschiedenen Isotopen darstellte. Und das war die rein physikalische Anwendung der Methode, mit der J. J. Thomson 1896 erstmalig Masse, Ladung und Geschwindigkeit des Elektrons, eines negative Elektrons, gemessen hatte, 1896. Und er wandte dieselbe Methode zur Messung der Ladung der positiven Ionen in der elektrischen Entladung von Gasen bei sehr geringem Druck, die positive Strahlen genannt werden, an. Und diese positiven Strahlen, die Anodenstrahlen genannt werden und von Goldstein entdeckt wurden, wurden Anfang 1900 von einem deutschen Physiker namens Wilhelm Wien, soweit ich weiß, untersucht. Und er hat nachgewiesen, dass die Masse des positiven Strahls nie geringer ist als das einzelne Wasserstoffatom. Das war die Essenz. Die Frage nach der Bedeutung der Isotope für das moderne Wissen wird zweifelsohne unterschiedlich beantwortet - abhängig davon, ob man ein Philosoph oder eher praktisch orientiert ist. Die Isotope haben Denkanstöße für beide Richtungen gegeben. Für den Chemiker mit der Seele eines Poeten, wenn es denn solche gibt, können nur wenige Entdeckungen mit dem philosophischen Interesse rivalisieren, das die Isotope gefunden haben - konkret in der Sprache von Keats. Wir hatten die Ehre, dem Vortrag von Dr. Hahn zuhören zu können. Und ich habe bereits auf den seltsamen Umstand hingewiesen, dass niemand daran glaubte, dass sich Madame Curies epochale Arbeit über Uran-Mineralien für Thorium-Mineralien wiederholen lassen würde. Der Zufall wollte es, dass der erste Teil der ursprünglichen Arbeiten, die Professor Hahn durchgeführt hatte - er hat ja über dieses Thema berichtet, für das er heute als der größte lebende Meister der Radiochemie gilt -, zunächst etwas beinhaltete, was heute für ein vollständig unmögliches Ergebnis gehalten wird, nämlich die Trennung der beiden Isotope Thorium und Radiothorium durch einfache chemische Mittel. Als Forschungsstudent bei Sir William Ramsay hatte er das Glück, wie er sagte, ein neues Element der Thoriumzerfallsreihe zu entdecken. Das hier ist die Thoriumzerfallsreihe. Das hier ist seine Entdeckung, nämlich Radiothorium. Bei der Analyse eines Minerals, das bekanntlich kein Thorium enthielt, hatte Fresenius durch einen einfachen Fehler im deutschen Standardlehrbuch der Analyse bei der Erfassung dieses Minerals das neue Mineral aus Ceylon mit der Bezeichnung Thorianit erfasst, das nicht mit Thorit verwechselt werden darf, und einen hohen Anteil an Uran, aber dennoch hauptsächlich Thorium enthält. Es war von Edelsteinsuchern in Ceylon auf der Suche nach Juwelen entdeckt worden und vom wissenschaftlichen Leiter des Eton College namens Porter nach Großbritannien importiert worden. Er schickte es zur Analyse an Ramsays Labor und erhielt aufgrund eines Fehlers in der Fresenius-Analyse als Ergebnis hauptsächlich Plutonium. Und das ging dann in die Fabrik und sollte entsprechend der Methode von Madame Curie aufbereitet werden. All das erfuhr Hahn von Ramsay und er wollte die Pionierarbeit von Madame Curie zu Uranmineralien mit einem anderen Mineral wiederholen und Erfahrungen im Isolieren von Radium sammeln. Hahn erhielt also dieses Material und niemand glaubte wirklich daran, dass sich die Arbeit von Madame Curie für die Thorium-Mineralien wiederholen ließ und ähnliche Ergebnisse erbringen würde. Das war acht Jahre nach den ursprünglichen Arbeiten von Madame Curie. Und als Hahn dann Radiothorium entdeckte, wobei es sich um einen Körper mit einer erheblichen Lebensdauer von zwei oder drei Jahren handelt - der Alpha-Strahl, der im Laufe der Zeit während des Zerfalls Beta-Strahlen erzeugt - versuchten alle anderen Chemiker, Radiochemiker weltweit, das Gleiche zu wiederholen und blieben dabei völlig erfolglos. Hätten sie Radiothorium isolieren können, das gewöhnliche kommerzielle Thoriumsalz erzeugen können, wäre das mindestens genauso wertvoll gewesen wie Radium, aber mit längerer Lebensdauer. Und es stellte sich heraus, dass Hahn tatsächlich das Unmögliche gelungen war. Aber die Erklärung lieferten - und das ist eine weitere seltsame historische Anekdote - bereits 1907 zwei amerikanische Chemiker, nämlich McCoy und Ross, die nach dem vergeblichen Ausprobieren aller bekannten Methoden zur Reinigung von Thorium in dem Versuch, Radiothorium zu isolieren, von dessen Existenz sie aufgrund seiner Radioaktivität wussten, die Originalität und den Mut besaßen, steif und fest zu behaupten - und das war bereits im Jahre 1907 eine simple Umsetzung der Isotop-Idee - dass sich Radiothorium und Thorium ihrer Meinung nach nicht durch chemische Mittel trennen lassen. Aber wie hat unser Zauberkünstler Hahn, zur damaligen Zeit ein blutiger Anfänger, das dann geschafft? In der Zwischenzeit hatte er, wie er Ihnen erzählte, den Atlantik überquert und arbeitete mit Rutherford in Montreal zusammen. Dort war er auf Mesothorium gestoßen, ein neues Mitglied der Thorium-Zerfallsreihe. Anders als Radiothorium (unverständlich 61:02) ... ist dies ein sehr kurzlebiges Element, das eine Lebensdauer von wenigen Jahren aufweist, damit jedoch erheblich länger als Radiothorium. Einen der Schritte, den Hahn durchgeführt hatte, war die Isolierung des Thoriums vom Radiothorium ... Er entdeckte das Radiothorium, das nicht das war, das er von dem untrennbaren Mineral getrennt hatte (unverständlich 61:30), sondern frisches Radiothorium, das er "herangezogen" hatte, ein äußerst schwieriger Vorgang. McCoy und Ross wiesen korrekterweise darauf hin, welch ein völlig unerwarteter Sachverhalt hier tatsächlich entdeckt worden war und unweigerlich früher oder später entdeckt werden musste, dass nämlich das Atom zerfiel. Hahn hatte in Wirklichkeit Mesothorium und Thorianit getrennt, ohne das zu erkennen. Es gibt keine nennenswerten Strahlen. Und das hat im Laufe der Zeit zum schnellen Entstehen einer neuen Radiothorium-Ernte geführt, die Hahn entdeckt hatte. Er hatte in Wirklichkeit die einfachen chemischen Trennungen des Mesothoriums von Thorium und des Radiothoriums von Mesothorium erreicht. Das ursprüngliche Radiothorium im Mineral blieb, wie auch heute noch, völlig untrennbar vom Hauptbestandteil. Wie hätte ein so unglaubliches Geheimnis, das von der Natur so lang und sorgsam gehütet worden war, eleganter entdeckt werden können? An ihren Früchten sollt ihr sie erkennen. Das gilt nicht nur für Bäume und für Menschen, sondern auch für all die unwahrscheinlichen Dinge wie Elemente oder Atome. Was Hahn und Ramsay bei ihrer Arbeit mit Thorianit wie Gärtner ausführten, war der Versuch, rote Tulpen von blauen zu trennen, wenn sie bereits verblüht sind. Diese Aufgabe erfordert keinen Gärtner. Jeder, der nicht farbenblind ist, kann sie erledigen. Was die anderen Chemiker taten, war dagegen der Versuch, es von Thorium zu isolieren, es zu trennen, bevor es geblüht hat und dazu war natürlich kein Gärtner in der Lage. Im Nachhinein lassen sich die Schwierigkeiten, von denen selbst kleinste erfolgreiche Entdeckungsschritte begleitetet waren, leicht unterschätzen. Die Schwierigkeiten von McCoy und Ross, die sie 1907 erfolgreich überwanden, waren so groß, dass das meiner Meinung nach Anerkennung verdient. Es sieht so einfach aus, nachdem sie bereits das Verschiebungsgesetz entdeckt hatten. Aber bedenken Sie, dass zur damaligen Zeit nicht einmal bekannt war, dass sich das Produkt einer radioaktiven Umwandlung notwendigerweise chemisch von seinen Eltern unterscheiden muss. Wenn, so Hahns erster Gedanke, Radiothorium und Thorium in der Reihe hintereinanderstehen, hätte Radiothorium unter keinen Umständen jeglicher Art entdeckt werden können. Ich denke, dass wir manchmal die Dinge im Kopf haben sollten, die wir nicht entdecken können, statt bei denen zu verweilen, die wir entdecken können. Andererseits gibt es in der Praxis nur wenige Entdeckungen in diesem Jahrhundert, die sich als so enormer Boom für die Menschheit herausstellten wie die Isotope. Ich möchte nur erwähnen, dass wir auch die Ehre haben, dass der Pionier auf diesem Gebiet unter uns weilt. Wir haben ihn bereits gehört, nämlich Professor George de Hevesy, der diese Elemente schon frühzeitig, bevor die Bezeichnung "Isotope" überhaupt geprägt wurde, als Tracer-Elemente verwendete und sie später auf die biologische und medizinische Forschung ausdehnte. Das ist wahrscheinlich das einzige, was die Öffentlichkeit jemals über Isotope gehört hat. Aber jetzt, wo der künstliche Atomzerfall möglich wurde und Elemente beliebig mit diese neuen leistungsstarken Instrumenten in Amerika, von denen wir gehört haben, aufgebaut oder abgebaut werden können, ist es möglich, radioaktive Isotope fast aller gewöhnlichen Elemente herzustellen - natürlich nach wie vor in völlig unwägbaren Mengen, was aber keine Rolle spielt, da man nicht mit den Gewichten zu tun hat, sondern mit der Radioaktivität. Und es gibt weitere radioaktive Isotope unter den 400 oder 500 üblichen Isotopen der gewöhnlichen Elemente, wie ich bereits gezeigt habe. Wenn ich auf meine weit zurückliegende Jugend zurückschaue, als es noch unmöglich war, Atome nach Belieben aufzuspalten und aufzubauen, scheint mir die Wissenschaft im Vergleich zu dem, was sie heute ist, damals in einem vorbereitenden, primitiven Stadium gewesen zu sein. Fast könnte man sagen, dass sie noch die Schulbank gedrückt hat. Welche Entdeckungen auch in Zukunft noch in der Wissenschaft der Materie gemacht werden und oder auch nicht: Was wir heute wissen und vor einem halben Jahrhundert noch nicht wussten, wird die Menschheit weit bringen. Eine wesentliche Bedingung dafür ist wohl, dass der Krieg auf Erden abgeschafft werden muss, bevor es zu spät ist. Es sollte kein Zweifel darüber bestehen, dass das die einhellige Meinung aller Wissenschaftler ist, die sich je zu dieser brennenden Frage geäußert haben.

Frederick Soddy on the amazing discoveries made by the Curies
(00:24:39 - 00:27:55)

 

The Curies and Becquerel jointly received the Nobel Prize in Physics for their discoveries in 1902, and in 1911, Marie Curie obtained another Nobel Prize, this time in Chemistry, for the discovery of radium and polonium. The findings greatly puzzled the scientific community; how could these elements spontaneously emanate energy on their own, without changing their external features? This was, as Soddy called it, “a new heterogeneity in matter”. Marie Curie admitted in a paper for the Revue Scientifique in 1900, that radioactivity abolishes the laws of chemistry that were then known. At around the same time, at McGill University in Montreal, Ernest Rutherford, a physicist from New Zealand, and Frederick Soddy, a chemist from England, set to work to unearth the cause and nature of radioactivity. Rutherford had already succeeded in characterising two types of radiation – the easily-absorbed, stable alpha-rays (now known to consist of two protons and two neutrons) and penetrating, short-lived beta-rays (electrons). The deeper penetrating gamma-rays, photons produced by the nucleus, were characterised by Paul Villard in 1900. Rutherford was particularly bewildered by the fact that radioactive elements were exuding types of radioactive gas, which he called “emanations”.

Experiments by Rutherford and Soddy performed during their eighteen-month collaboration showed that radioactivity is not a singular event. Radioactive elements spontaneously transform into other elements with different characteristics, which in turn transform into still other elements; a type of cascade, during which radiation is produced. Additionally, the time it takes for half of the atoms of a radioactive element to decay is constant and characteristic of that element. This property became known as the element’s half-life. Rutherford realised that radioactive decay of elements could be used as a type of clock, which could calculate the age of the Earth, yet another scientific riddle that could not be solved by generations of scientists.

Rutherford and Soddy were very careful when publishing the results of their work. This was more than a curious phenomenon. The transformation of matter seemed almost magical, and they did not want to be regarded as alchemists. However, both Rutherford and Soddy were awarded the Nobel Prize in Chemistry – Rutherford in 1908, “for his investigations into the disintegration of the elements, and the chemistry of radioactive substances”, and Soddy in 1921, “for his contributions to our knowledge of the chemistry of radioactive substances, and his investigations into the origin and nature of isotopes”. In the ten years following his work in Montreal, Soddy concentrated his research on how to incorporate the rising number of new chemical elements into the long-established periodic table. By 1913, Soddy had concluded that the new series of radioactive elements were not so much new elements as different forms of the same element, with identical chemical properties but different atomic weights. He called these forms “isotopes”, from the Greek words isos (equal) and tópos (place), as chemical isotopes have the same place in the periodic table, but are characterised by a different mass and half-life. During his lecture in Lindau in 1954, Soddy called isotopes “one of nature’s best-kept secrets”.

The neutral subatomic particle

In 1910, Rutherford, having already received his Nobel Prize, made yet another extraordinary discovery. He and his assistants Hans Geiger and Ernest Marsden conducted an experiment, where alpha particles were thrown at a piece of gold foil. Astonishingly, approximately 1 in 20 000 of the alpha particles were deflected from the foil – these particles were clearly hitting something dense at the core of the gold atoms. Rutherford concluded that the atom has a small, positively-charged nucleus, which is covered in a cloud of spinning, negatively-charged electrons. By 1920, Rutherford put forward the idea that the nucleus consists of a neutral particle, with no electric charge, probably formed from a proton and electron. However, it took several years before experiments could determine the presence of a neutral particle. Studies were carried out by Walter Bothe and Herbert Becker, where beryllium was hit with alpha particles, which caused its’ disintegration and radiation. Irène and Frédéric Joliot-Curie repeated the experiment, but directed the radiation at a paraffin wax sample, which ejected what they thought were high-energy protons from hydrogen atoms. James Chadwick, a physicist who had worked with Rutherford for many years, realised that these high-energy particles must be heavy neutral particles ejected from the nucleus. In 1932, after only two weeks of experiments, Chadwick submitted the paper, “The Possible Existence of a Neutron”, which was followed by the paper, “The Existence of a Neutron” a few months later. Chadwick received the Nobel Prize in Physics for the discovery of the neutron in 1935. This soon proved to be more than the identification of another subatomic particle. Scientists in the United States, Great Britain, France, Germany, and Italy were intensely searching for ways to release large amounts of energy by penetrating atomic nuclei with the heavy neutron. The frenzy in experimental nuclear physics developed in parallel with political unrest in Europe. In 1933, Leo Szilard patented the idea of a nuclear chain reaction, where nuclei bombarded by a neutron could produce two or more neutrons. The turning point was when Otto Hahn and Lise Meitner described nuclear fission of uranium, whereby the neutron is absorbed by the heavy nucleus of uranium (235U), which turns into an excited state (236U) and then splits into two isotopes of barium and krypton, ejecting neutrons and a large amount of kinetic energy. These findings greatly alarmed nuclear physicists in the United States, particularly Leo Szilard, Enrico Fermi and Albert Einstein, who decided to warn President Roosevelt himself of the possibility of the use of nuclear weapons in the near future. This led to the establishment of the Uranium Committee, which eventually became the Manhattan Project in 1942. At a recent meeting in Lindau, Nobel Laureate Roy J. Glauber explained nuclear fission in the introduction of his lecture:

 

Roy Glauber (2016) - Some Recollections of the Manhattan Project 1943-1945

How do you do? I have gotten a slightly late start. And I hope you’ll pardon me. It’s of course a late start in describing what happened about 70 years ago. Now, what I’m going to try to do is to relate to you some of the experiences and some of the memories I have from a period when I was in fact just 18 years old. The year was 1943. I want first, however, to go back just a bit prior to that. And let me see if I can get this system working. Can you see Enrico Fermi? The year was 1938 and he had been doing a succession of experiments using neutrons. Neutrons were the neutral particle that resides in the nucleus but only discovered really in about 1931. There were many mysteries before that. That clarification led to a great many experiments that could be done. And Fermi was primary among the experimenters in discovering what it was that neutrons did to nuclei. He did a long succession of such experiments in the middle 1930s. Some of the last experiments he did would shine a beam of neutrons on uranium, the heaviest of the known nuclei at that time. He discovered quite a complex of things going on but had no time to analyse them because he not only received the Nobel Prize but used that as the occasion to himself, for himself and his family to leave Italy. After visiting Stockholm briefly he went to Columbia University in New York. And there really began a great deal of the story that I am going to tell you. He left many questions unsettled regarding what neutrons do to uranium. One of the greatest of the radio chemists of the day, Otto Hahn, began investigating that seriously and discovered that there was quite a variety of particles that emerged from these neutron-uranium collisions and they had chemical properties which were absolutely bewildering. As a radio chemist, he could verify that several elements at least that emerged from these collisions had the same properties as familiar and much lighter elements. The person who really resolved this problem was also a refugee at the time. In 1938 she left Berlin, aided by Otto Hahn, her boss, and settled in Stockholm where with a nephew of hers, Otto Frisch, this woman, who was Lise Meitner, developed the theory that what was happening was in fact a split up of the uranium nucleus. That 2 fragments, approximately half the mass of the original uranium nucleus, were emerging. And there were many chemical consequences because this was a variety of nuclei, roughly in the middle of the atomic table. Now, this idea which in fact was hers, she was never rewarded for it, did lead to quite some activity. In particular Leo Szilard, a young Hungarian who loved thinking of the future, realised that these were nuclei being produced which had a few neutrons too many. That not only would these fission fragments, these heavy fission fragments emerge but more neutrons. He was aware, in other words, that it might be possible to create a neutron chain reaction. And disturbed by the possibilities that might be opened by that, he decided that he had to communicate with Franklin Roosevelt, the president, and see to it that America was aware of the dangers involved. He wrote a letter on behalf of Albert Einstein to Roosevelt. And here he is meeting with Einstein at a summer vacation spot in 1939 at the end of Long Island, drafting that letter which Einstein was happy to sign. And that letter was then transmitted by a well-known banker to Roosevelt who was duly impressed and appointed the only technically trained person he would know who was the leader, the chairman of the Bureau of Standards in Washington, Vannevar Bush, and asked him to put together a committee to look further into this matter. Well, here you have that committee. It, as you can see, was seemingly a rather joyous occasion to these people, 3 or 4 of them Nobel Prize winners. Including in the centre you had James Conant who was President of Harvard University but who in fact was a chemist! And well, I won’t go through the naming of these worthy individuals but the truth of the matter is that besides enjoying themselves and appointing still other committees they did virtually nothing. (Laughter) So that is, I think, really the true introduction to this matter. A man who was peripherally involved was Kenneth Bainbridge who was a mass spectroscopist at Harvard and who told us the correct masses of the various fragments that were coming off in uranium fission which was thereby understood for the first time. Bainbridge also built a cyclotron. Here he is proud of his new cyclotron. The year must have been about 1940 or ’41 when the cyclotron was completed. As the interest in doing experiments with fission arose. And there was even a desire to do more experiments. Here you have someone whom you will recognise as Robert Wilson. There in the centre is Robert Wilson whom you'll recognise. I think he was at that point at Princeton University, years later at Cornell, and finally the director of the Fermi laboratory in America, the great accelerator laboratory in the mid-west. But here he was negotiating on behalf of a fictitious organisation called the St. Louis Medical Depot, trying to secure the cyclotron itself and have it shipped somewhere to the west. Where was it being shipped? Well, many people by late 1943 had learned one particular address. This was it. It was the only information I was given when I turned 18 and had had quite a few of the courses as they existed at the time, most of the graduate courses, and was asked to go to this place. Well, this place was Post Office Box 1663. And I shortly learned, you know a post office box in America is about the size of a shoe box. And it might have had some difficulty accommodating the 2 trunks of books and belongings I sent there. But just imagine the difficulty that it must have had accommodating the moving vans and freight cars full of materials that everybody else was sending to this location. We were not even sure it was in New Mexico – but that was where we were being sent. In fact it turned out to be not Santa Fe, but Lamy, which is a tiny wooden rail station about 15 or so miles from Santa Fe. Well, there was a man who got off the train when I did. He wore a Derby hat and a navy blue overcoat and he announced that his name was Mr. Newman. Well, when we got to Santa Fe, where there was a small office run by the project, and signed the register I could see that his name was in fact John von Neumann. He was in fact the author of one of the famous texts I had been reading at just that time. He was met, I should say, by someone who looked for all the world like a cowboy. He wore inevitably dungarees, a checked shirt and in fact a ten-gallon hat. He seemed to be a cowboy of some sort, hired as a chauffeur. And there started a conversation, a really remarkable conversation, between Mr. Newman and this 'cowboy', whom I later discovered was in fact Jack Hawking, a member of the theory group and a mathematician at the laboratory. The trip up to the laboratory was geographically remarkable. This is a picture taken a little later. The original bridge across the Rio Grande, which runs north-south there, had been in fact washed out and you can see it in the background here, that’s the original bridge. This was a bridge that appeared about a year later on the way up to what we call 'the hill' which was back here behind these great bluffs. We had to drive north some distance to Espanola in order to cross the Rio Grande and go back south and this was the sort of vista. There were magnificent vistas that began to unfold as we climbed up into the Jemez Mountains. That’s the main chain, the Sangre de Cristo Mountains, you see, literally looking across the Rio Grande in the bottom of that valley. Here is where we got to the entrance to the project area such as it was. It was on a plateau which was high above the Rio Grande valley, about 7,000 feet of altitude. It turned out that this plateau was crossed by a great many canyons so that the country would be virtually impassable, except by the 1 or 2 roads that led to a nearby pueblo ruin. Well, that’s the entrance. When it got a little busier a few weeks later there were many MPs examining the credentials of people wanting to get in. And many stories conveyed back out by the truck drivers and various individuals not bearing any responsibility to the project but just telling about bizarre things they had seen up there on the hill. This is something called 'the big house'. What was up there was the Los Alamos Ranch School for Boys. In particular several parents, whose sons had tubercular problems and were sent to this school to get a high school education and at the same time breathe the fresh clean air of New Mexico. And if I jump ahead now, it became a laboratory. It became a laboratory with a fenced area which was quite considerable in size. It had many buildings, laboratory buildings within it. And when finally they made the place look much more respectable – this is the way the gate looked but this was not there, I would have to say, for the first 2 or 3 years. Here is how people’s credentials and baggage were examined entering the technical area. I just happened to get hold of this picture because the man being interrogated is Robert Marshak who was a group leader in the project. After the project was going for a year or 2 there was a fair amount of construction and in fact much of it rather awkward. The technical area had begun on this side of the road but had soon filled the area up to the fences. And they decided they had to move to the other side of the main road. And the only way of managing the problem of examining people’s credentials was to construct elevated passageways across the road to take you from one part of the technical area to another. This happened eventually to be E building or the seat of the theoretical division which I was made a tiny part of. Now, to move further ahead, this was typical housing for 4 families. Most of the people at the laboratory were very young. They were families just beginning with the result that the hospital, for example, had quite a high birth rate relative to the population. These young families were producing more people than virtually any other army-run hospital. (Laughter) The housing varied quite a bit. I like this particular picture, not just because it showed the way people live but a forest fire in the distance. The country was very dry. Virtually no water at all, except for a carefully managed pond in the middle of the Mesa, and it was a devil of a job trying to put out even those very tiny forest fires. Here is more housing. Here is some housing unique in that it had all the single women in the laboratory, about 12 or 14 of them. This is what a dormitory room looked like - not mine but you couldn’t have told mine from this one. It was a single room in a temporary structure which at least kept people out of the elements, out of the rain, and where we occasionally held dormitory parties. There were other features there. A great many young men who were being drafted and whom the government - there was no established means of determining people’s talents when they entered the army. So people with quite a variety of different talents were thought perhaps to have engineering skills or something of the sort and were sent to Los Alamos to live in these barracks. The assignments they had were, as war time assignments go, pretty interesting and kept them very busy. But unfortunately the army felt that this group of privates ought to have some officer leadership. These officers were people who had no technical training whatever and could see no purpose in their being there other than to give drills to these engineers. Getting them up at 6 in the morning, having them line up and exacting from them whatever calisthenics or drills were considered beneficial. It led to a great deal of complaint. These were men who had, as far as the army is concerned, very safe and useful positions but you never heard so much complaining in your life. In later years - there’s this little monument which was not there. This is where the original faculty of the Los Alamos Ranch School for Boys lived. There were several such stone houses. Now, of the people who were there the man who headed the theory division was Hans Bethe. He was a remarkable choice in that he was unbelievably versatile. He could give you a 2-significant-figure estimate of virtually any ridiculous problem that you could invent on the spur of the moment. He was an extraordinary leader for the theory division. Here is the leader of the entire project – Robert Oppenheimer. And he too was an extraordinary leader. For one thing, of course, you never saw him except with a cigarette in his mouth. He was a great teacher but didn’t believe in making things easy for anybody. He expressed himself in literary, at times almost poetic, terms and in that way he had the admiration of a great many rough-and-tumble scientists who were really very impressed by him. Wherever he went, and he visited every part of the project including all of the experiments, you would see his porkpie-hat as a kind of calling card. Now, another figure, who was away when I first came there in January of ’44, had gone off in a huff. He had left and, in fact, abandoned the project for a month until Oppenheimer talked him into returning and promised him a certain sector of the project as his own fiefdom as it were. Edward Teller had done a certain amount of work on thermonuclear reactions, possible astrophysical thermonuclear reactions, and he had adopted as his primary interest securing a burning process of some sort in among the light hydrogen isotopes, in particular deuterium and tritium. He was persuaded that somehow the nuclear bomb could be used as a match to light that continuing fire. He believed in that passionately and felt that he had been altogether neglected in the original organisation of Los Alamos. Oppenheimer had at that point to persuade him to come back. And come back he did. And you have heard a great deal about what he did subsequently. This is Emilio Segrè, Segrè had been a collaborator with Fermi in Rome. He was already in America and he had been given a remarkable sort of assignment in the early days in Los Alamos. Which was to go to an isolated place in one of the canyons where the neutron background would be minimal and determine whether the newly created element, plutonium, in particular the form in which it was created in the nuclear reactors in Chicago, to determine whether that particular nucleus underwent spontaneous fission to any considerable extent. That was important because spontaneous fission meant that there would be neutrons bouncing around within the material whatever materials you were using. And the original plan for creating the bomb was a relatively simple one of shooting a cylinder of, it was in that case uranium 235, shooting that cylinder into a hollowed-out cylinder in a spherical mass. And neither of these 2 masses of uranium 235 would be above the critical point. They would not individually support chain reactions. But when amalgamated, when joined together, they would indeed. Now, there was a difficult period of time while you were assembling these pieces and if, indeed, a chain reaction started in that period it would be pre-detonation and you’d get a much smaller explosion. In uranium 235 the spontaneous fission rate was slow enough so that that was not a serious danger. If one used a canon to thrust the cylindrical projectile into the hollowed-out volume one would have milliseconds to do that in. And that was just possible with a canon. However, Segrè discovered very quickly that the spontaneous fission rate in plutonium which was even by that time being produced more rapidly than uranium 235 which required isotope separation, that the spontaneous fission rate and the background of neutrons would mean that you would have to assemble the plutonium bomb in microseconds rather than milliseconds. A microsecond is millionth of a second. And that was the principle problem that the entire project had really to deal with in the subsequent years. Now, here is the rest of Segrè’s group. And I just show you what a group looked like and what the background and the technical area looked like. But here in the back behind Segrè you have Owen Chamberlain who was inseparable from him. And the 2 of course won the Nobel Prize several years later in Berkeley for using the Bevatron to identify the anti-proton. That’s Martin Deutsch. At that point I’m afraid I can’t recognise the other faces too easily. Well, here is another familiar figure, Dick Feynman. Feynman was not only an extraordinarily creative mathematician for theoretical problems, he was also a bit of a clown and a performer. Whenever you saw a cluster of a few women who were around, you would discover that they were clustered around Feynman who was performing. Feynman was always performing. And some of us got to hear his stories, later collected by Ralph Leighton, the son of Robert Leighton. It was Leighton who wrote the books “Surely You’re Joking, Mr. Feynman!” and the subsequent ones. Anyway, he was certainly one of the most prominent characters at Los Alamos. Here is the way we heard colloquia, sitting in canvas chairs which were put out in the gymnasium after the place had been searched down thoroughly for any lurking gymnasts or spies. And here is our friend, the Polish mathematician, whose name slips me at this moment but you probably all know better than I, who actually solved the problem of how to ignite the 'Super', as it was called, the thermonuclear reaction in the light elements. And here he is on a bench sitting in the Plaza of Santa Fe with von Neumann and Feynman. Now, presently I’ll run through just some pictures of individuals. This is perhaps the most famous individual we had in the place whose name was Nicholas Baker. At least that’s the name that was broadcast on the PA system, because one of the most unspoken names in the place was 'Niels Bohr'. Bohr always spoke up but never said very much. And whatever it was he said you could not really resolve because Danish is a language not given to high resolution (laughter) and because he was forever puffing on that pipe. Now, what he would do is to scratch matches, take a deep draft of match smoke and strike one match after another. That would go on all day. I have here a picture of Bohr with his son Aage who accompanied him everywhere. This is a picture which does not come from Los Alamos. It’s very typical of Copenhagen. Anyway, the 2 were an inseparable pair. Aage, who by the way also received the Nobel Prize, not for the most effective nuclear model of the day in the early 1950s, not for anything that necessarily related him to the Bohr family. Now, the man who directed the project officially was Leslie Groves. He was a rather heavy-set man with a very military mind and remarkably little understanding of science considering the nature of the project that he was dealing with. Here is a rather idealised painting that was made of him (laughter) and which now is to be seen there. General Groves and Oppenheimer often appeared together. They were not pretending to be the Gold Dust Twins. They represented really the 2 things that went on: Military authority which was in a sense the propulsion what made the whole thing go, and the intelligence that directed it on the other hand. Well, the one thing one could do in the winter was ski. There were many ski parties, rather primitive ones, they were wooden skis as a rule and the simplest of poles. This was a group that included Fermi, Bethe, Weisskopf and a couple of others. I won’t delay you with all the names. This is a photo I’ve included because it dates from about 1931 and it involves many of the same characters. They all knew one another. There is Heisenberg. And if there was such a project, and on a certain plane there was such a project as this in Germany, it was Heisenberg who was the principle authority. But sitting next to him is Rudolf Peierls who ran the project, and who really initiated the project in Britain. And in the background you have people from several other locations. Victor Weisskopf was a young student at the time. And Felix Bloch, fairly young himself. George Placzek. A man who worked on the same sorts of things in Italy was Gian-Carlo Wick in the background. These people all knew one another. Now, it was a large project. This is the electromagnetic separation plant in Tennessee. Here in Hanford, Washington, is the reactor complex that actually produced the plutonium. And there are many stories connected with that which there is no time for. Let me introduce a couple of stories which you probably never did hear about Los Alamos. There was a need to calibrate the explosion that was planned for the Trinity test. How would one calibrate that explosion? What did you have to work with? Well, the inspiration was another explosion. So this is the platform from which that would be created. Here is literally 100 tons of TNT on a wooden platform which was in fact exploded well in advance of the Trinity test in order simply to calibrate their instruments. Here is another strange thing: a piece of steel, a steel tank, as a matter of fact. And we were assured that it was the largest ever fabricated. It was quite thick steel. This was as it was being shipped to Los Alamos. The reason for this was that the original tests would not have involved very high explosives for the assembly of the bomb but it was thought that the material was infinitely precious uranium 235 or plutonium had somehow to be saved. You couldn’t just let that be dispersed everywhere. So you had to try, given whatever explosive means you had, to use in order to assemble the bomb. The idea was to be able to collect the pieces and salvage the fissionable material. So this was a tank promptly named 'Jumbo' - it was the name of a mystical elephant at the time. Here it was being shipped to Los Alamos. Now, was Jumbo ever used? Well, it was realised that the explosive means that was necessary to assemble the bomb was going to be a bit too much even for that tank. And so it was never used. Whatever it cost and whatever it involved getting it from Pittsburgh all the way to the New Mexican desert. Someone after the war – this is a post-war development – decided to find out what would happen if he put several pounds of TNT inside this tank. (Laughter) And that’s the result. Let me move on very quickly to Trinity. I’m afraid we’re running a bit late. This is a 100 foot tower that was set up, the bomb to be placed on the top. The point was to keep its detonation away from the ground so that the ground not contaminate the explosion. Let the explosion take place up 100 feet. Well, here it is. There is the bomb. Not quite assembled yet but sitting atop the tower. Here exercising his curiosity to see the thing is – you can see who that is, can’t you, just from the silhouette. Oppenheimer wouldn’t have missed going up the tower to examine the bomb before it was detonated. Here you have a much more complete assembly of the bomb. These were all detonation devices to detonate in effect a sphere of high explosive. And this was a very complex sphere because it was a sphere which had not simply to explode outward but to create a blast wave that converged spherically upon the material in the centre. It was an extraordinary development that and probably the central one at Los Alamos. Here is the explosion after the first couple of milliseconds. This is the explosion at Trinity. Here it is a second or 2 later. Here is what was left seen from the air. The sand surrounding the tower was turned to a greenish sort of fused glass. And every last bit of it taken up by souvenir seekers presently. The circle you see here, this is where the 100 ton explosion was set off, just ordinary TNT in order to calibrate the instrumentation. And here are the first individuals coming in and looking at the stumps left over from the tower. The tower above had of course been completely evaporated. And this was one of the 4 supports of the tower. There, inevitably again, is the inseparable pair, Oppenheimer and General Groves. This is Victor Weisskopf off on the right. I don’t immediately recognise any of the others. Well, when we saw that - and I happen to have seen that explosion take place. As a theorist I was not welcome at the Trinity site, and so some of us managed to drive cars, which were even pretty scarce then, to the top of a peak, Sandia Peak near Albuquerque, where we had quite a distant view. And I managed by staying there all night and waiting until 5.30 in the morning, which was about 4 hours after we expected the blast to take place. I saw what amounted to a sunrise in the south. A very short time later there was a sunrise in the east. Well, here is what went on in the 3 weeks following the mid-July Trinity test. This was on Tinian Island. This is the implosion bomb, the spherical one. And also, by the way, that was the one tested at the Trinity site. And as you know it worked and that was a cause for celebration by 2 people out of 3 in the Potsdam conference. Truman had been informed about the test immediately. Stalin was probably not informed immediately, but he was surely informed. And there was a bit of a celebration when the war ended, involving of course General Groves and the President of the University of California who formally directed and oversaw the project. But President Sproul had never set foot in the place and never seen, it’s not even clear that he had known about the existence of the project. Oppenheimer, of course, became something of a celebrity. And a year later in the Harvard commencement you had this collection of people: Conant again sitting in the centre, General Marshal who was about to unveil the Marshal plan, General Omar Bradley and here somewhat lost off in the corner is J. Robert Oppenheimer, a Harvard alumnus. And I must say this was quite a reunion seeing him there again. He became something of a celebrity. Now, I don’t know how much further to go with all of this because there are a great many pictures and it’s gotten a bit late for the end of this talk. Maybe if there is a slide machine where we will be talking in the afternoon? It's said I will be with some students, and maybe we can put the slides, the remainder of the slides together. There are a few interesting ones. But they have entirely to do with post-war matters. This is a collection of theorists who gathered at Shelter Island 2 years after the end of the war. But there’s a considerable number of names you would recognise in that. Let me cut it off here in order not to run too substantially over and I’ll see if we can do more this afternoon. Thank you.

Wie geht es Ihnen? Ich bin etwas spät dran, und ich hoffe, Sie sehen es mir nach. Es ist natürlich für die Beschreibung der Ereignisse vor 70 Jahren ein bisschen spät. Ich werde aber versuchen, Ihnen einige meiner Erfahrungen und Erinnerungen aus der Zeit zu vermitteln, als ich erst 18 Jahre alt war. Es war das Jahr 1943. Zunächst möchte ich aber noch ein Stück weiter zurückgehen. Lassen Sie mich sehen, ob ich dieses System zum Laufen bekomme. Können Sie Enrico Fermi sehen? Das war 1938 und er hatte eine ganze Reihe von Experimenten mit Neutronen durchgeführt. Neutronen sind die neutralen Teilchen, die sich im Kern befinden, aber erst wirklich ungefähr im Jahr 1931 entdeckt wurden. Es gab vorher viel Geheimnisvolles. Diese Klärung führte zu einer Vielzahl an Experimenten, die durchgeführt werden konnten. Und Fermi war der Erste unter den Experimentatoren, der entdeckte, was die Neutronen mit dem Kern machten. Er führte Mitte der Dreißigerjahre eine ganze Reihe solcher Experimente durch. Einige seiner letzten durchgeführten Experimente war, einen Neutronenstrahl auf Uran zu richten, dem schwersten bekannten Kern zu der Zeit. Er entdeckte, dass ganz komplexe Dinge passierten, hatte aber keine Zeit, sie zu analysieren, weil er nicht nur den Nobelpreis bekam, sondern dies auch als die Gelegenheit nahm, um mit seiner Familie Italien zu verlassen. Nach einem kurzen Besuch in Stockholm ging er an die Columbia-Universität in New York. Und damit begann ein großer Teil der Geschichte, die ich Ihnen erzählen werde. Er ließ viele Fragen offen, was die Neutronen mit dem Uran machten. Einer der damalig größten Radiochemiker, Otto Hahn, begann das ernsthaft zu untersuchen und entdeckte, dass sehr unterschiedliche Teilchen aus diesen Neutron-Uran-Stößen herauskamen und diese hatten absolut verwirrende chemische Eigenschaften. Als Radiochemiker konnte er verifizieren, dass zumindest mehrere Elemente, die aus diesen Stößen austraten, die gleichen Eigenschaften hatten wie bekannte und viel leichtere Elemente. Die Person, die dieses Problem tatsächlich löste, war zu der Zeit auch ein Flüchtling. Im Jahr 1938 verließ sie Berlin unter Mithilfe von Otto Hahn, ihrem Chef, und ließ sich in Stockholm bei einem ihrer Neffen nieder, Otto Frisch. Diese Frau war Lise Meitner, und sie entwickelte die Theorie, dass es eine Spaltung des Urankerns war, was tatsächlich passierte. Dass zwei Fragmente von ungefähr der Hälfte der Masse des ursprünglichen Urankerns herauskamen. Und es gab viele chemische Konsequenzen, wegen dieser Vielfalt der Kerne, ungefähr in der Mitte des Periodensystems. Nun, diese Idee war in Wirklichkeit ihre - sie wurde nie dafür belohnt -, und führte zu einer Menge an Aktivitäten. Insbesondere Leo Szilard, ein junger Ungar, der schrecklich gerne in die Zukunft dachte, realisierte, dass diese produzierten Kerne ein paar Neutronen zu viel besaßen. Nicht nur würden diese schweren Spaltungsfragmente herauskommen, sondern mehrere Neutronen. Mit anderen Worten, ihm war bewusst, dass es möglich wäre, eine Neutronenkettenreaktion zu erzeugen, und er war über die Möglichkeiten beunruhigt, die sich dadurch eröffneten. Er entschied, dass er mit Franklin Roosevelt, dem Präsidenten der USA, kommunizieren und sicherstellen müsste, dass Amerika die damit verknüpften Gefahren bewusst waren. Er schrieb einen Brief im Auftrag von Albert Einstein an Roosevelt. Und hier trifft er sich im Jahr 1939 mit Einstein an einem Sommerferienort am Ende von Long Island und entwarf den Brief, den Einstein dann gerne unterschrieb. Dieser Brief wurde dann durch einen recht bekannten Bankier Roosevelt übergeben, der ordentlich beeindruckt war. Der ernannte dann die einzige ihm bekannte Person mit technischer Ausbildung, Vannevar Bush, Vorsitzender des Bureau of Standards in Washington, und bat ihn, ein Komitee zu gründen, das sich dieser Sache weiter annehmen sollte. Nun, hier haben sie das Komitee. Wie man sehen kann, war es offensichtlich ein ziemlich freudiges Ereignis für diese Leute, von denen 3 oder 4 Nobelpreisträger waren. In der Mitte befindet sich James Conant, der Präsident der Harvard Universität war, aber eigentlich war er Chemiker. Und nun werde ich nicht die Namen der ehrenwerten Personen durchgehen, aber die Wahrheit ist, dass sie fast nichts machten, außer sich zu vergnügen und noch weitere Komitees zu ernennen. So, das ist, denke ich, wirklich die wahre Einführung in diese Geschichte. Der Mann, der am Rande involviert war, war Kenneth Bainbridge, der in Harvard Massenspektroskopie machte und uns die wahren Massen der verschiedenen Fragmente nannte, die durch die Uranspaltung entstanden und welche dadurch zum ersten Mal richtig verstanden wurde. Bainbridge hatte auch ein Zyklotron gebaut. Hier ist er, stolz auf sein neues Zyklotron. Es muss ungefähr im Jahr 1940 oder 41 gewesen sein, als das Zyklotron fertiggestellt wurde. Und das Interesse an Experimenten mit der Kernspaltung stieg an. Und es gab sogar den Wunsch, noch weitere Experimente durchzuführen. Hier ist jemand, den einige von Ihnen als Robert Wilson erkennen werden. Dort in der Mitte ist Robert Wilson, wie Sie erkennen können. Ich denke, zu der Zeit war er in Princeton, Jahre später in Cornell und schließlich der Direktor des Fermi-Labors in Amerika, dem großen Beschleunigerlabor im mittleren Westen. Aber hier verhandelt er für eine fiktive Organisation namens St. Louis Medical Depot und versucht, das Zyklotron zu bekommen und es irgendwo in den Westen zu transportieren. Wohin sollte es verschickt werden? Nun, viele Menschen kannten bis Ende 1943 eine bestimmte Adresse, diese hier. Das war die einzige Information, die ich bekam, als ich 18 wurde. Ich hatte eine Reihe von Kursen besucht, wie es sie zu der Zeit gab, die meisten Graduiertenkurse, und wurde gebeten, zu dieser Adresse zu gehen. Nun, diese Adresse war Postfach 1663. Und kurz danach bekam ich mit - wissen Sie, ein Postfach in Amerika hat ungefähr die Größe eines Schuhkartons. Und es wäre etwas schwierig gewesen, die zwei Koffer mit Büchern und meiner Habe, die ich dorthin geschickt hatte, aufzunehmen. Aber stellen Sie sich einmal die Schwierigkeiten vor, die Umzugslaster und Frachtlaster voll mit Material aufzunehmen, die alle anderen an diese Adresse geschickt hatten. Wir waren uns noch nicht einmal sicher, dass es in New Mexico war. Dorthin wurden wir nämlich geschickt. In der Tat stellte sich heraus, dass es nicht Santa Fe war, sondern Lamy, ein kleiner hölzerner Bahnhof ungefähr 20 Kilometer von Santa Fe entfernt. Nun, da war ein Mann, der auch wie ich aus dem Zug stieg. Er trug eine Melone und einen marineblauen Mantel und verkündete, sein Name wäre Mr. Newman. Als wir in Santa Fe ankamen, gab es dort ein kleines Büro für das Projekt, und als ich mich eintrug, konnte ich sehen, dass sein Name tatsächlich John von Neumann war. Er war tatsächlich der Autor eines berühmten Buchs, das ich damals gerade las. Er traf jemand, der für alle wie ein Cowboy aussah. Er trug die zwangsläufigen Jeans, ein kariertes Hemd und tatsächlich einen breitrandigen Cowboyhut. Er schien irgendein Cowboy zu sein, der als Fahrer gemietet war. Und dann begann eine Unterhaltung. Eine wirklich bemerkenswerte Unterhaltung zwischen Mr. Newman und diesem Cowboy, der, wie ich später herausfand, tatsächlich Jack Hawking, ein Mitglied der Theoriegruppe und Mathematiker im Labor war. Die Fahrt hoch zum Labor war geografisch bemerkenswert. Dies ist ein etwas später aufgenommenes Bild. Die ursprüngliche Brücke über den Rio Grande, der dort von Norden nach Süden verläuft, war nämlich unterspült – Sie können sie im Hintergrund sehen, das ist die ursprüngliche Brücke. Dies war eine Brücke, die ungefähr ein Jahr später auftauchte, auf dem Weg zu dem 'Hügel', wie wir ihn nannten, der hier hinten zwischen den großen Klippen war. Wir mussten eine Weile nach Norden nach Espanola fahren, um über den Rio Grande zu kommen und dann wieder nach Süden, und da hatten wir diese Aussicht. Es gab immer wieder fantastische Aussichten, während man in die Jemez-Berge hochfuhr. Das ist die Hauptkette, die Sangre-de-Cristo-Berge; man sieht buchstäblich über den Rio Grande zum Talboden. Hier kommen wir zum Eingang des Projektgebiets, wie es damals war. Es befand sich auf einem Plateau, das sich hoch über dem Rio-Grande-Tal befand, auf ungefähr 2100 Metern über dem Meer. Es stellte sich heraus, dass das Plateau von vielen tiefen Schluchten durchzogen war, sodass das Land fast undurchquerbar war, mit Ausnahme der ein oder zwei Straßen, die zu einer nahen Puebloruine führten. Dies ist der Eingang. Als es ein paar Wochen später ein wenig betriebsamer wurde, gab es dort viele Militärpolizisten, die die Papiere von Leuten überprüften, die hinein wollten. Und die vielen Geschichten, die von den Lasterfahrern und von vielen Leuten erzählt wurden, die keine Verantwortung für das Projekt hatten, aber viele absonderliche Dinge erzählten, die sie dort oben auf dem Hügel gesehen hatten. Dies wurde 'das große Haus' genannt. Dort oben gab es die Los Alamos Farmschule für Jungen. Insbesondere mehrere Eltern, deren Söhne Tuberkuloseprobleme hatten, wurden auf diese Schule geschickt, um eine weiterführende Bildung zu erhalten und gleichzeitig die frische, reine Luft von New Mexico zu atmen. Und wenn ich jetzt etwas in die Zukunft springe, es wurde ein Labor. Es wurde ein Labor mit einem eingezäunten Gebiet, das eine sehr beträchtliche Größe hatte. Es gab viele Gebäude, Laborgebäude darin. Und als sie schließlich das viel respektabler gestalteten – so sah das Tor aus, aber das gab es nicht, sagen wir mal, während der ersten 2, 3 Jahre. So wurden die Papiere und das Gepäck überprüft, wenn man das technische Gebiet betrat. Ich habe dieses Bild zufällig bekommen, da der Mann, der dort befragt wird, Robert Marshak ist, einer der Gruppenleiter im Projekt. Nachdem das Projekt schon 1 oder 2 Jahre lief, gab es eine ganze Menge Bauaktivitäten, und viel davon etwas umständlich. Das technische Gebiet begann auf dieser Straßenseite, aber hat schon bald das Gebiet bis zu den Zäunen ausgefüllt. Und sie entschieden, dass sie auf die andere Seite der Straße bauen müssten. Und der einzige Weg, das Problem der Überprüfung der Papiere zu handhaben, war, erhöhte Korridore über die Straße zu bauen, um von einem Teil des technischen Gebiets in ein anders zu kommen. Dies war schließlich dann das E-Gebäude oder der Sitz der Theorieabteilung, von dem ich ein kleiner Teil wurde. Nun, um weiterzumachen, dies war die typische Unterbringung für 4 Familien. Die meisten Leute im Labor waren sehr jung. Es gab Familiengründungen, mit dem Ergebnis, dass beispielsweise das Krankenhaus, bezogen auf die Bevölkerung, eine recht hohe Geburtenrate hatte. Diese jungen Familien produzierten mehr Menschen als nahezu jedes andere Krankenhaus der Armee. (Lachen) Die Unterbringung variierte beträchtlich. Ich mag dieses Bild, nicht nur, weil es zeigt, wie die Leute leben, sondern auch wegen des Waldbrands im Hintergrund. Das Land war sehr trocken. Fast überhaupt kein Wasser, ausgenommen einen sorgfältig gepflegten Teich in der Mitte des Plateaus. Und es war höllisch schwierig, selbst sehr kleine Waldbrände zu löschen. Hier noch mehr Unterkünfte. Hier eine einzigartige Unterkunft, da dort alle unverheirateten Frauen aus dem Labor lebten, etwa 12 oder 14 von ihnen. So sah ein Wohnheimraum aus - nicht meiner, aber man hätte ihn nicht von meinem unterscheiden können. Es war ein Einzelzimmer in einem Behelfsbau, der die Menschen wenigstens vor dem Wetter, dem Regen schützte, und wo wir gelegentlich Wohnheimparties feierten. Dort gab es noch andere Besonderheiten. Viele junge Leute, die eingezogen wurden und denen die Regierung – es gab keine etablierten Wege, das Talent der Leute zu bestimmen, wenn sie zur Armee kamen. Viele Leute mit einer Vielfalt an unterschiedlichen Talenten - vielleicht dachte man, sie hätten Ingenieurkenntnisse oder Ähnliches - wurden nach Los Alamos geschickt, um in diesen Baracken zu leben. Die Aufgaben, die sie hatten, waren für Kriegsaufgaben ziemlich interessant und hielten sie auf Trab. Aber unglücklicherweise glaubte die Armee, dass diese Gruppe von Soldaten die Führung eines Offiziers benötigte. Diese Offiziere waren Menschen, die überhaupt keine technische Ausbildung hatten und keinen Sinn darin sahen, dort zu sein, wenn sie nicht diese Ingenieure etwas exerzieren ließen. Sie weckten sie um 6 Uhr morgens, und sie mussten sich in einer Linie aufstellen und irgendeine Gymnastik oder Exerzierübung durchführen, die für dienlich gehalten wurde. Das führte zu jeder Menge Beschwerden. Diese Männer hatten, soweit es die Armee betraf, sehr sichere und nützliche Stellungen, aber man hat noch nie im Leben so viele Beschwerden gehört. In späteren Jahren gab es dieses kleine Denkmal, das es damals nicht gab. Dort lebte der ursprüngliche Lehrkörper der Los Alamos Farmschule für Jungen. Es gab mehrere solcher Steinhäuser. Nun, von den Leuten, die dort waren, dieser Mann, der die Theorieabteilung leitete, war Hans Bethe. Es war eine bemerkenswerte Wahl, da er unbeschreiblich vielseitig war. Er konnte einem eine auf 2 Stellen genaue Schätzung für wirklich jede irrwitzige Aufgabe geben, die man aus dem Ärmel schüttelte. Es war ein außergewöhnlicher Leiter für die Theorieabteilung. Hier ist der Leiter des gesamten Projekts – Robert Oppenheimer. Er war ebenfalls ein außergewöhnlicher Leiter. Zum einen sah man ihn natürlich nie ohne Zigarette im Mund. Er war ein großartiger Lehrer, hielt aber nichts davon, es irgendjemandem einfach zu machen. Er drückte sich literarisch aus, manchmal fast poetisch, und so wurde er von vielen einfachen Wissenschaftlern bewundert, die von ihm wirklich sehr beeindruckt waren. Wo auch immer er hinging, und er besuchte jeden Teil des Projekts einschließlich aller Experimente, sah man seinen flachen Hut, der eine Art Visitenkarte war. Eine weitere Persönlichkeit, die tatsächlich abwesend war, als ich zuerst im Januar 1944 dort hinkam, war beleidigt weggegangen. Er war gegangen und hatte das Projekt einen Monat lang verlassen, bevor Oppenheimer ihn überredete, wiederzukommen. Und er versprach ihm einen bestimmten Projektteil sozusagen als seinen eigenen Machtbereich. Edward Teller hatte schon auf dem Gebiet der thermonuklearen Reaktionen gearbeitet, mögliche astrophysikalische Reaktionen, und hatte als sein primäres Interesse ausgewählt, irgendeinen Brennprozess zwischen den leichten Wasserstoffatomen herzustellen, insbesondere Deuterium und Tritium. Er war überzeugt, dass man irgendwie die Atombombe als ein Zündholz für das andauernde Feuer verwenden kann. Er glaubte leidenschaftlich daran und meinte, dass er in der ursprünglichen Organisation von Los Alamos ziemlich vernachlässigt worden war. Oppenheimer musste ihn damals überzeugen zurückzukommen, und das tat er dann auch. Sie haben schon viel davon gehört, was er danach gemacht hat. Dies ist Emilio Segrè, Segrè war ein Mitarbeiter Fermis in Rom. Er war bereits in Amerika und hatte eine ungewöhnliche Aufgabe in den Anfängen von Los Alamos: Die Aufgabe war, an einen isolierten Platz in einem der Täler zu gehen, wo der Neutronenuntergrund minimal war, um zu bestimmen, ob das neu geschaffene Element Plutonium, insbesondere in der Form, in der es durch die Atomreaktoren in Chicago erzeugt wurde, und zu bestimmen, ob dieser spezielle Kern in einem beträchtlichen Umfang eine spontane Spaltung zeigte. Das war wichtig, weil spontane Spaltung bedeutete, dass Neutronen überall innerhalb des Materials herumfliegen würden, was immer das Material war, das man benutzte. Und der ursprüngliche Plan, eine Bombe herzustellen, war ein relativ einfacher: Man wollte einen Zylinder, in diesem Fall aus Uran 235, diesen Zylinder in einen ausgehöhlten Zylinder in einer Kugelmasse schießen. Und keine dieser 2 Massen aus Uran 235 wäre über dem kritischen Punkt. Sie würden einzeln keine Kettenreaktion unterstützen. Aber wenn sie verschmolzen, wenn sie zusammengefügt sind, dann würden sie das allerdings. Das war eine schwierige Zeit, während man diese Stücke zusammenbrachte und wenn tatsächlich in der Zeit eine Kettenreaktion startete, wäre das eine vorzeitige Detonation und man bekäme eine viel kleinere Explosion. Im Uran 235 war die spontane Spaltungsrate langsam genug, dort gab es also keine ernste Gefahr. Wenn man eine Kanone benutzte, um das zylindrische Projektil in das hohle Volumen zu schießen, dann hätte man Millisekunden, um es zu tun. Und das war gerade noch möglich mit einer Kanone. Segrè entdeckte aber sehr schnell, dass die spontane Spaltungsrate in Plutonium, das sogar zu der Zeit schneller produziert wurde als Uran 235, das eine Isotopentrennung benötigte, dass die spontane Spaltungsrate und der Neutronenuntergrund bedeuteten, dass man die Plutoniumbombe in Mikrosekunden und nicht Millisekunden zusammenbringen musste. Eine Mikrosekunde ist ein Millionstel einer Sekunde. Und das war das Hauptproblem, mit dem das gesamte Projekt in den Folgejahren zu kämpfen hatte. Nun, hier ist der Rest von Segrès Gruppe. Und nur um Ihnen zu zeigen, wie die Gruppe aussah und wie der Hintergrund und das technische Gebiet aussah. Aber hier im Hintergrund hinter Segrè ist Owen Chamberlain, der unzertrennlich von ihm war. Und die beiden bekamen mehrere Jahre später den Nobelpreis für die Nutzung des Bevatrons in Berkeley für die Identifizierung des Antiprotons. Das ist Martin Deutsch. Hier, fürchte ich, kann ich die anderen Gesichter nicht leicht erkennen. Hier ist eine andere bekannte Person, Dick Feynman. Feynman war nicht nur ein außergewöhnlich kreativer Mathematiker für theoretische Aufgaben, er war auch ein bisschen Clown und Entertainer. Sobald ein paar von den Frauen, die es dort gab, zusammenkamen, sah man, dass sie sich um Feynman scharten, der etwas zum Besten gab. Feynman gab immer den Unterhalter. Und einige von uns hörten seine Geschichten, wie sie von Ralph Leighton, Robert Leightons Sohn, später gesammelt wurden. Es war Leighton, der die Bücher „Sie belieben wohl zu scherzen, Mr. Feynman!“ und die darauffolgenden schrieb. Er war sicherlich einer der markantesten Charaktere in Los Alamos. So haben wir Kolloquien gehört, in Segeltuchstühlen sitzend, die in einer Turnhalle aufgestellt wurden, nachdem sie gründlich nach irgendwelchen versteckten Turnern oder Spionen durchsucht worden war. Und hier ist unser Freund, der polnische Mathematiker, an dessen Namen ich mich im Moment nicht erinnern kann, aber Sie kennen ihn wahrscheinlich besser als ich, der tatsächlich die Aufgabe löste, die 'Super', wie wir sie nannten, zu zünden, die thermonukleare Reaktion der leichten Elemente. Und hier sitzt er auf einer Bank in der Plaza von Santa Fe mit von Neumann und Feynman. Nun, jetzt gehe ich einfach einige Bilder von Personen durch. Dies ist die vielleicht berühmteste Person, die wir dort hatten, er hieß Nicholas Baker. Wenigstens war das der Name, der über die Lautsprecheranlage durchgegeben wurde, weil dort einer der am meisten unausgesprochenen Name Niels Bohr war. Bohr sagte immer etwas, aber er sprach nie sehr viel. Und was auch immer er sagte, konnte man nicht auflösen, weil das Dänische keine Sprache ist, die zu einer hohen Auflösung neigt, und weil er immer seine Pfeife schmauchte. Nun, er zündete ständig Streichhölzer an, nahm einen tiefen Zug des Streichholzrauchs, und zündete ein Streichholz nach dem anderen an. Das setzte sich den gesamten Tag fort. Ich habe hier ein Bild von Bohr mit seinem Sohn Aage, der ihn überall hin begleitete. Dieses Bild kommt nicht aus Los Alamos, es ist typisch für Kopenhagen. Die beiden waren unzertrennlich. Aage, der übrigens auch den Nobelpreis erhielt, aber nicht für das damals effektivste Kernmodell in den frühen 1950er-Jahren, nicht für etwas, was ihn notwendigerweise mit der Bohrfamilie verband. Der Mann, der das Projekt offiziell leitete war Leslie Groves. Er war ein ziemlich korpulenter Mann mit einem militärischen Verstand und erstaunlich wenig Verständnis für die Wissenschaft angesichts der Art des Projekts, das er leitete. Hier ist ein ziemlich idealisiertes Gemälde, das von ihm angefertigt wurde und dort angeschaut werden kann. General Groves und Oppenheimer erschienen oft zusammen. Sie gaben nicht vor, unzertrennlich zu sein. Sie repräsentierten aber die 2 Dinge, die präsent waren: militärische Autorität, die so etwas wie der Antrieb war, der Dinge vorantrieb, und die Intelligenz, die es andererseits lenkte. Was man im Winter wirklich machen konnte, war Skifahren. Es gab viele Skigruppen, ziemlich primitive, es waren normalerweise hölzerne Skis und die einfachsten Stöcke. Diese Gruppe schloss Fermi, Bethe, Weisskopf und ein paar andere ein. Ich will Sie nicht mit all den Namen langweilen. Ich habe dieses Foto mit drin, weil es aus dem Jahr 1931 stammt und viele derselben Menschen zeigt. Sie kannten sich alle. Das ist Heisenberg. Wenn es so ein Projekt gab, und auf irgendeine Weise gab es sicherlich so ein Projekt in Deutschland, dann war Heisenberg die oberste Autorität. Aber neben ihm sitzt Rudolf Peierls, der das Projekt in Großbritannien leitete und eigentlich initiierte. Und im Hintergrund stehen Menschen von vielen anderen Orten. Victor Weisskopf war zu der Zeit ein junger Student. Und Felix Bloch war auch noch ziemlich jung. George Placzek. Ein Mann, der an derselben Art von Dingen in Italien arbeitete war Gian-Carlo Wick im Hintergrund. Diese Leute kannten sich alle. Nun, es war ein großes Projekt. Dies ist die elektromagnetische Trennungsanlage in Tennessee. Hier in Hanford, Washington, ist der Reaktorkomplex, der tatsächlich das Plutonium produzierte. Und damit verbunden gibt es viele Geschichten, aber ich habe keine Zeit dafür. Lassen Sie mich ein paar Geschichten über Los Alamos erzählen, die Sie vermutlich noch nie gehört haben. Es gab die Notwendigkeit, die Explosion, die für den Trinity-Test geplant wurde, zu kalibrieren. Wie würde man diese Explosion kalibrieren? Womit konnte man arbeiten? Nun, die Eingebung war eine weitere Explosion. So, dies ist die Plattform, von der das erzeugt werden würde. Hier sind 100 Tonnen TNT auf einer hölzernen Plattform, die tatsächlich weit vor dem Trinity-Test zur Explosion gebracht wurden, um einfach die Kalibration ihrer Instrumente zu prüfen. Hier ist noch etwas Merkwürdiges: ein Haufen Stahl, eigentlich ein Stahltank. Uns wurde versichert, dass es der größte jemals gebaute Tank war. Es war recht dicker Stahl. Dies war zu der Zeit, als er nach Los Alamos transportiert wurde. Der Grund dafür war, dass die ursprünglichen Tests keine hochexplosiven Stoffe für den Zusammenbau der Bombe involviert hätten, aber man dachte, dass das Material, wie beispielsweise Uran 235 oder Plutonium, so unendlich kostbar wäre und irgendwie gesammelt werden müsste. Man konnte das nicht einfach überall verstreuen. Man musste daher versuchen, was auch immer als Sprengstoff vorlag, um die Bombe zusammenzubauen. Die Idee war, dass man die Bruchstücke sammeln und das Spaltmaterial retten könnte. Also wurde dieser Tank auch prompt 'Jumbo' genannt - zu der Zeit war das der Name eines mystischen Elefanten. Hier wird er nach Los Alamos transportiert. Nun, wurde Jumbo jemals benutzt? Man fand heraus, dass der Sprengstoff, der für die Bombe notwendig war, selbst für diesen Tank etwas zu kraftvoll war. Und daher wurde er nie benutzt. Was auch immer an Kosten und sonst noch damit verbunden war, ihn von Pittsburgh den ganzen Weg bis in die Wüste in New Mexico zu bekommen. Nach dem Krieg - dies ist eine Entwicklung nach dem Krieg - entschied sich jemand herauszufinden, was passieren würde, wenn man mehrere Pfund TNT in den Tank geben würde. Und das ist das Ergebnis. (Lachen) Lassen Sie mich schnell zu Trinity übergehen. Ich fürchte, wir sind ein wenig spät dran. Dies ist ein 33-Meter-Turm, der gebaut wurde, um die Bombe an die Spitze zu setzen. Die Sache war die, die Explosion vom Boden wegzuhalten, damit der Boden nicht die Explosion kontaminierte, die Explosion in einer Höhe von 33 Metern stattfinden zu lassen. Nun, hier ist sie. Dort ist die Bombe. Nicht ganz fertig zusammengebaut, aber schon an der Spitze des Turms. Hier befriedigt er seine Neugier, das Ding zu sehen – Sie können erkennen, wer das ist, nicht wahr, nur von der Silhouette. Oppenheimer hätte es sich nie nehmen lassen, den Turm hochzuklettern, um die Bombe zu inspizieren, bevor sie explodierte. Hier ist ein vollständigerer Zusammenbau der Bombe. Dies waren all die Explosionsvorrichtungen, um eine Kugel an hochexplosiven Stoffen effektiv zu detonieren. Und es war eine sehr komplizierte Kugel, weil die Kugel nicht einfach nach außen explodieren sollte, sondern eine Explosionswelle erzeugen sollte, die kugelförmig nach innen zu dem Material in der Mitte konvergiert. Das war eine außergewöhnliche Entwicklung und vielleicht die wichtigste in Los Alamos. Hier ist die Explosion nach den ersten paar Millisekunden. Das ist die Explosion von Trinity. Hier eine oder zwei Sekunden später. Hier ist das, was übrig geblieben ist, aus der Luft. Der Sand um den Turm herum hatte sich in grünliches, geschmolzenes Glas verwandelt. Und jedes letzte bisschen wurde sofort von Souvenirjägern eingesammelt. Der Kreis, den Sie hier sehen, dort wurden die 100 Tonnen zur Explosion gebracht, nur gewöhnliches TNT, um die Instrumente zu kalibrieren. Und hier die ersten Menschen, die kamen und sich die Stummel ansahen, die vom Turm übrig waren. Der Turm darüber war natürlich komplett verdampft. Und dies war einer der 4 Stützen des Turms. Dort ist wieder die beiden Unzertrennlichen, Oppenheimer und General Groves. Dort ist Victor Weisskopf auf der rechten Seite. Ich kann die anderen gerade nicht erkennen. Nun, als wir das sahen - und ich gehörte zu denen, die die Explosion sahen. Als Theoretiker war ich nicht auf dem Trinity-Gelände willkommen, und so schafften es einige von uns, an Autos zu kommen, die damals ziemlich rar waren, und auf einen Berg zu fahren, Sandia Peak in der Nähe von Albuquerque, wo wir eine weite Sicht hatten. Ich blieb dort die ganze Nacht bis 5.30 Uhr morgens, das war 4 Stunden nach der erwarteten Explosionszeit. Ich sah etwas, das wie ein Sonnenaufgang im Süden war. Kurze Zeit später gab es einen Sonnenaufgang im Osten. Dies passierte in den 3 Wochen, die dem Trinity-Test Mitte Juli folgten. Dies war auf der Insel Tinian. Das ist die Implosionsbombe, die kugelförmige. Und das war auch die, die auf dem Trinity-Gelände getestet wurde. Und wie Sie wissen, funktionierte sie und das war ein Grund zum Feiern für 2 von 3 Leuten auf der Potsdamer Konferenz. Truman wurde sofort über den Test informiert worden. Stalin wurde wahrscheinlich nicht sofort informiert, aber er war sicher informiert. Und es gab eine Feier, nachdem der Krieg zu Ende war, natürlich mit General Groves und dem Präsidenten der Universität von Kalifornien, die formal das Projekt leitete und überwachte. Aber Präsident Sproul hat nie den Ort besucht und ihn nie gesehen; es ist nicht einmal klar, ob er von der Existenz des Projekts gewusst hatte. Oppenheimer wurde natürlich eine Berühmtheit. Und ein Jahr später bei der Harvard-Abschlussfeier gab es diese Versammlung: Conant sitzt wieder in der Mitte, General Marshall, der dabei war, den Marshallplan bekannt zu geben, General Omar Bradley und hier etwas verloren in der Ecke ist J. Robert Oppenheimer, ein Harvard-Alumnus. Und ich muss sagen, es war ganz speziell, ihn dort wieder zu treffen. Er wurde eine Berühmtheit. Nun, ich weiß nicht, wie viel weiter ich gehen soll, weil es noch eine Menge an Bildern gibt und es inzwischen recht spät für das Ende dieses Vortrags ist. Vielleicht, wenn es einen Diaprojektor dort gibt, wo wir am Nachmittag sind. Ich werde dort mit einigen Studenten zusammen sein, und vielleicht können wir die restlichen Dias zusammen anschauen. Es gibt da noch ein paar interessante. Aber sie haben ausschließlich mit Dingen nach dem Krieg zu tun. Dies ist eine Versammlung von Theoretikern, die sich 2 Jahre nach Ende des Krieges auf Shelter Island trafen. Aber es gibt eine beträchtliche Anzahl von Namen, die Sie dort wiedererkennen würden. Lassen Sie mich hier abbrechen, um nicht zu sehr zu überziehen, und dann schauen wir, was wir heute Nachmittag tun können. Vielen Dank.

Roy Glauber on nuclear fission
(00:00:27 - 00:06:56)

 

 “It’s a terrible thing that we made” – Robert R. Wilson, as quoted by Richard P. Feynman

The Manhattan Project brought together talented physicists from all over the country with the aim of constructing an atomic bomb. The headquarters of the top-secret project were in “an unstated and distant location”, as Glauber writes in the abstract of his talk; Los Alamos, New Mexico. Many of those working on the science behind the project were present or future Nobel Laureates. In this lecture fragment, Glauber describes the Trinity test, the first nuclear weapon ever detonated:

 

Roy Glauber (2016) - Some Recollections of the Manhattan Project 1943-1945

How do you do? I have gotten a slightly late start. And I hope you’ll pardon me. It’s of course a late start in describing what happened about 70 years ago. Now, what I’m going to try to do is to relate to you some of the experiences and some of the memories I have from a period when I was in fact just 18 years old. The year was 1943. I want first, however, to go back just a bit prior to that. And let me see if I can get this system working. Can you see Enrico Fermi? The year was 1938 and he had been doing a succession of experiments using neutrons. Neutrons were the neutral particle that resides in the nucleus but only discovered really in about 1931. There were many mysteries before that. That clarification led to a great many experiments that could be done. And Fermi was primary among the experimenters in discovering what it was that neutrons did to nuclei. He did a long succession of such experiments in the middle 1930s. Some of the last experiments he did would shine a beam of neutrons on uranium, the heaviest of the known nuclei at that time. He discovered quite a complex of things going on but had no time to analyse them because he not only received the Nobel Prize but used that as the occasion to himself, for himself and his family to leave Italy. After visiting Stockholm briefly he went to Columbia University in New York. And there really began a great deal of the story that I am going to tell you. He left many questions unsettled regarding what neutrons do to uranium. One of the greatest of the radio chemists of the day, Otto Hahn, began investigating that seriously and discovered that there was quite a variety of particles that emerged from these neutron-uranium collisions and they had chemical properties which were absolutely bewildering. As a radio chemist, he could verify that several elements at least that emerged from these collisions had the same properties as familiar and much lighter elements. The person who really resolved this problem was also a refugee at the time. In 1938 she left Berlin, aided by Otto Hahn, her boss, and settled in Stockholm where with a nephew of hers, Otto Frisch, this woman, who was Lise Meitner, developed the theory that what was happening was in fact a split up of the uranium nucleus. That 2 fragments, approximately half the mass of the original uranium nucleus, were emerging. And there were many chemical consequences because this was a variety of nuclei, roughly in the middle of the atomic table. Now, this idea which in fact was hers, she was never rewarded for it, did lead to quite some activity. In particular Leo Szilard, a young Hungarian who loved thinking of the future, realised that these were nuclei being produced which had a few neutrons too many. That not only would these fission fragments, these heavy fission fragments emerge but more neutrons. He was aware, in other words, that it might be possible to create a neutron chain reaction. And disturbed by the possibilities that might be opened by that, he decided that he had to communicate with Franklin Roosevelt, the president, and see to it that America was aware of the dangers involved. He wrote a letter on behalf of Albert Einstein to Roosevelt. And here he is meeting with Einstein at a summer vacation spot in 1939 at the end of Long Island, drafting that letter which Einstein was happy to sign. And that letter was then transmitted by a well-known banker to Roosevelt who was duly impressed and appointed the only technically trained person he would know who was the leader, the chairman of the Bureau of Standards in Washington, Vannevar Bush, and asked him to put together a committee to look further into this matter. Well, here you have that committee. It, as you can see, was seemingly a rather joyous occasion to these people, 3 or 4 of them Nobel Prize winners. Including in the centre you had James Conant who was President of Harvard University but who in fact was a chemist! And well, I won’t go through the naming of these worthy individuals but the truth of the matter is that besides enjoying themselves and appointing still other committees they did virtually nothing. (Laughter) So that is, I think, really the true introduction to this matter. A man who was peripherally involved was Kenneth Bainbridge who was a mass spectroscopist at Harvard and who told us the correct masses of the various fragments that were coming off in uranium fission which was thereby understood for the first time. Bainbridge also built a cyclotron. Here he is proud of his new cyclotron. The year must have been about 1940 or ’41 when the cyclotron was completed. As the interest in doing experiments with fission arose. And there was even a desire to do more experiments. Here you have someone whom you will recognise as Robert Wilson. There in the centre is Robert Wilson whom you'll recognise. I think he was at that point at Princeton University, years later at Cornell, and finally the director of the Fermi laboratory in America, the great accelerator laboratory in the mid-west. But here he was negotiating on behalf of a fictitious organisation called the St. Louis Medical Depot, trying to secure the cyclotron itself and have it shipped somewhere to the west. Where was it being shipped? Well, many people by late 1943 had learned one particular address. This was it. It was the only information I was given when I turned 18 and had had quite a few of the courses as they existed at the time, most of the graduate courses, and was asked to go to this place. Well, this place was Post Office Box 1663. And I shortly learned, you know a post office box in America is about the size of a shoe box. And it might have had some difficulty accommodating the 2 trunks of books and belongings I sent there. But just imagine the difficulty that it must have had accommodating the moving vans and freight cars full of materials that everybody else was sending to this location. We were not even sure it was in New Mexico – but that was where we were being sent. In fact it turned out to be not Santa Fe, but Lamy, which is a tiny wooden rail station about 15 or so miles from Santa Fe. Well, there was a man who got off the train when I did. He wore a Derby hat and a navy blue overcoat and he announced that his name was Mr. Newman. Well, when we got to Santa Fe, where there was a small office run by the project, and signed the register I could see that his name was in fact John von Neumann. He was in fact the author of one of the famous texts I had been reading at just that time. He was met, I should say, by someone who looked for all the world like a cowboy. He wore inevitably dungarees, a checked shirt and in fact a ten-gallon hat. He seemed to be a cowboy of some sort, hired as a chauffeur. And there started a conversation, a really remarkable conversation, between Mr. Newman and this 'cowboy', whom I later discovered was in fact Jack Hawking, a member of the theory group and a mathematician at the laboratory. The trip up to the laboratory was geographically remarkable. This is a picture taken a little later. The original bridge across the Rio Grande, which runs north-south there, had been in fact washed out and you can see it in the background here, that’s the original bridge. This was a bridge that appeared about a year later on the way up to what we call 'the hill' which was back here behind these great bluffs. We had to drive north some distance to Espanola in order to cross the Rio Grande and go back south and this was the sort of vista. There were magnificent vistas that began to unfold as we climbed up into the Jemez Mountains. That’s the main chain, the Sangre de Cristo Mountains, you see, literally looking across the Rio Grande in the bottom of that valley. Here is where we got to the entrance to the project area such as it was. It was on a plateau which was high above the Rio Grande valley, about 7,000 feet of altitude. It turned out that this plateau was crossed by a great many canyons so that the country would be virtually impassable, except by the 1 or 2 roads that led to a nearby pueblo ruin. Well, that’s the entrance. When it got a little busier a few weeks later there were many MPs examining the credentials of people wanting to get in. And many stories conveyed back out by the truck drivers and various individuals not bearing any responsibility to the project but just telling about bizarre things they had seen up there on the hill. This is something called 'the big house'. What was up there was the Los Alamos Ranch School for Boys. In particular several parents, whose sons had tubercular problems and were sent to this school to get a high school education and at the same time breathe the fresh clean air of New Mexico. And if I jump ahead now, it became a laboratory. It became a laboratory with a fenced area which was quite considerable in size. It had many buildings, laboratory buildings within it. And when finally they made the place look much more respectable – this is the way the gate looked but this was not there, I would have to say, for the first 2 or 3 years. Here is how people’s credentials and baggage were examined entering the technical area. I just happened to get hold of this picture because the man being interrogated is Robert Marshak who was a group leader in the project. After the project was going for a year or 2 there was a fair amount of construction and in fact much of it rather awkward. The technical area had begun on this side of the road but had soon filled the area up to the fences. And they decided they had to move to the other side of the main road. And the only way of managing the problem of examining people’s credentials was to construct elevated passageways across the road to take you from one part of the technical area to another. This happened eventually to be E building or the seat of the theoretical division which I was made a tiny part of. Now, to move further ahead, this was typical housing for 4 families. Most of the people at the laboratory were very young. They were families just beginning with the result that the hospital, for example, had quite a high birth rate relative to the population. These young families were producing more people than virtually any other army-run hospital. (Laughter) The housing varied quite a bit. I like this particular picture, not just because it showed the way people live but a forest fire in the distance. The country was very dry. Virtually no water at all, except for a carefully managed pond in the middle of the Mesa, and it was a devil of a job trying to put out even those very tiny forest fires. Here is more housing. Here is some housing unique in that it had all the single women in the laboratory, about 12 or 14 of them. This is what a dormitory room looked like - not mine but you couldn’t have told mine from this one. It was a single room in a temporary structure which at least kept people out of the elements, out of the rain, and where we occasionally held dormitory parties. There were other features there. A great many young men who were being drafted and whom the government - there was no established means of determining people’s talents when they entered the army. So people with quite a variety of different talents were thought perhaps to have engineering skills or something of the sort and were sent to Los Alamos to live in these barracks. The assignments they had were, as war time assignments go, pretty interesting and kept them very busy. But unfortunately the army felt that this group of privates ought to have some officer leadership. These officers were people who had no technical training whatever and could see no purpose in their being there other than to give drills to these engineers. Getting them up at 6 in the morning, having them line up and exacting from them whatever calisthenics or drills were considered beneficial. It led to a great deal of complaint. These were men who had, as far as the army is concerned, very safe and useful positions but you never heard so much complaining in your life. In later years - there’s this little monument which was not there. This is where the original faculty of the Los Alamos Ranch School for Boys lived. There were several such stone houses. Now, of the people who were there the man who headed the theory division was Hans Bethe. He was a remarkable choice in that he was unbelievably versatile. He could give you a 2-significant-figure estimate of virtually any ridiculous problem that you could invent on the spur of the moment. He was an extraordinary leader for the theory division. Here is the leader of the entire project – Robert Oppenheimer. And he too was an extraordinary leader. For one thing, of course, you never saw him except with a cigarette in his mouth. He was a great teacher but didn’t believe in making things easy for anybody. He expressed himself in literary, at times almost poetic, terms and in that way he had the admiration of a great many rough-and-tumble scientists who were really very impressed by him. Wherever he went, and he visited every part of the project including all of the experiments, you would see his porkpie-hat as a kind of calling card. Now, another figure, who was away when I first came there in January of ’44, had gone off in a huff. He had left and, in fact, abandoned the project for a month until Oppenheimer talked him into returning and promised him a certain sector of the project as his own fiefdom as it were. Edward Teller had done a certain amount of work on thermonuclear reactions, possible astrophysical thermonuclear reactions, and he had adopted as his primary interest securing a burning process of some sort in among the light hydrogen isotopes, in particular deuterium and tritium. He was persuaded that somehow the nuclear bomb could be used as a match to light that continuing fire. He believed in that passionately and felt that he had been altogether neglected in the original organisation of Los Alamos. Oppenheimer had at that point to persuade him to come back. And come back he did. And you have heard a great deal about what he did subsequently. This is Emilio Segrè, Segrè had been a collaborator with Fermi in Rome. He was already in America and he had been given a remarkable sort of assignment in the early days in Los Alamos. Which was to go to an isolated place in one of the canyons where the neutron background would be minimal and determine whether the newly created element, plutonium, in particular the form in which it was created in the nuclear reactors in Chicago, to determine whether that particular nucleus underwent spontaneous fission to any considerable extent. That was important because spontaneous fission meant that there would be neutrons bouncing around within the material whatever materials you were using. And the original plan for creating the bomb was a relatively simple one of shooting a cylinder of, it was in that case uranium 235, shooting that cylinder into a hollowed-out cylinder in a spherical mass. And neither of these 2 masses of uranium 235 would be above the critical point. They would not individually support chain reactions. But when amalgamated, when joined together, they would indeed. Now, there was a difficult period of time while you were assembling these pieces and if, indeed, a chain reaction started in that period it would be pre-detonation and you’d get a much smaller explosion. In uranium 235 the spontaneous fission rate was slow enough so that that was not a serious danger. If one used a canon to thrust the cylindrical projectile into the hollowed-out volume one would have milliseconds to do that in. And that was just possible with a canon. However, Segrè discovered very quickly that the spontaneous fission rate in plutonium which was even by that time being produced more rapidly than uranium 235 which required isotope separation, that the spontaneous fission rate and the background of neutrons would mean that you would have to assemble the plutonium bomb in microseconds rather than milliseconds. A microsecond is millionth of a second. And that was the principle problem that the entire project had really to deal with in the subsequent years. Now, here is the rest of Segrè’s group. And I just show you what a group looked like and what the background and the technical area looked like. But here in the back behind Segrè you have Owen Chamberlain who was inseparable from him. And the 2 of course won the Nobel Prize several years later in Berkeley for using the Bevatron to identify the anti-proton. That’s Martin Deutsch. At that point I’m afraid I can’t recognise the other faces too easily. Well, here is another familiar figure, Dick Feynman. Feynman was not only an extraordinarily creative mathematician for theoretical problems, he was also a bit of a clown and a performer. Whenever you saw a cluster of a few women who were around, you would discover that they were clustered around Feynman who was performing. Feynman was always performing. And some of us got to hear his stories, later collected by Ralph Leighton, the son of Robert Leighton. It was Leighton who wrote the books “Surely You’re Joking, Mr. Feynman!” and the subsequent ones. Anyway, he was certainly one of the most prominent characters at Los Alamos. Here is the way we heard colloquia, sitting in canvas chairs which were put out in the gymnasium after the place had been searched down thoroughly for any lurking gymnasts or spies. And here is our friend, the Polish mathematician, whose name slips me at this moment but you probably all know better than I, who actually solved the problem of how to ignite the 'Super', as it was called, the thermonuclear reaction in the light elements. And here he is on a bench sitting in the Plaza of Santa Fe with von Neumann and Feynman. Now, presently I’ll run through just some pictures of individuals. This is perhaps the most famous individual we had in the place whose name was Nicholas Baker. At least that’s the name that was broadcast on the PA system, because one of the most unspoken names in the place was 'Niels Bohr'. Bohr always spoke up but never said very much. And whatever it was he said you could not really resolve because Danish is a language not given to high resolution (laughter) and because he was forever puffing on that pipe. Now, what he would do is to scratch matches, take a deep draft of match smoke and strike one match after another. That would go on all day. I have here a picture of Bohr with his son Aage who accompanied him everywhere. This is a picture which does not come from Los Alamos. It’s very typical of Copenhagen. Anyway, the 2 were an inseparable pair. Aage, who by the way also received the Nobel Prize, not for the most effective nuclear model of the day in the early 1950s, not for anything that necessarily related him to the Bohr family. Now, the man who directed the project officially was Leslie Groves. He was a rather heavy-set man with a very military mind and remarkably little understanding of science considering the nature of the project that he was dealing with. Here is a rather idealised painting that was made of him (laughter) and which now is to be seen there. General Groves and Oppenheimer often appeared together. They were not pretending to be the Gold Dust Twins. They represented really the 2 things that went on: Military authority which was in a sense the propulsion what made the whole thing go, and the intelligence that directed it on the other hand. Well, the one thing one could do in the winter was ski. There were many ski parties, rather primitive ones, they were wooden skis as a rule and the simplest of poles. This was a group that included Fermi, Bethe, Weisskopf and a couple of others. I won’t delay you with all the names. This is a photo I’ve included because it dates from about 1931 and it involves many of the same characters. They all knew one another. There is Heisenberg. And if there was such a project, and on a certain plane there was such a project as this in Germany, it was Heisenberg who was the principle authority. But sitting next to him is Rudolf Peierls who ran the project, and who really initiated the project in Britain. And in the background you have people from several other locations. Victor Weisskopf was a young student at the time. And Felix Bloch, fairly young himself. George Placzek. A man who worked on the same sorts of things in Italy was Gian-Carlo Wick in the background. These people all knew one another. Now, it was a large project. This is the electromagnetic separation plant in Tennessee. Here in Hanford, Washington, is the reactor complex that actually produced the plutonium. And there are many stories connected with that which there is no time for. Let me introduce a couple of stories which you probably never did hear about Los Alamos. There was a need to calibrate the explosion that was planned for the Trinity test. How would one calibrate that explosion? What did you have to work with? Well, the inspiration was another explosion. So this is the platform from which that would be created. Here is literally 100 tons of TNT on a wooden platform which was in fact exploded well in advance of the Trinity test in order simply to calibrate their instruments. Here is another strange thing: a piece of steel, a steel tank, as a matter of fact. And we were assured that it was the largest ever fabricated. It was quite thick steel. This was as it was being shipped to Los Alamos. The reason for this was that the original tests would not have involved very high explosives for the assembly of the bomb but it was thought that the material was infinitely precious uranium 235 or plutonium had somehow to be saved. You couldn’t just let that be dispersed everywhere. So you had to try, given whatever explosive means you had, to use in order to assemble the bomb. The idea was to be able to collect the pieces and salvage the fissionable material. So this was a tank promptly named 'Jumbo' - it was the name of a mystical elephant at the time. Here it was being shipped to Los Alamos. Now, was Jumbo ever used? Well, it was realised that the explosive means that was necessary to assemble the bomb was going to be a bit too much even for that tank. And so it was never used. Whatever it cost and whatever it involved getting it from Pittsburgh all the way to the New Mexican desert. Someone after the war – this is a post-war development – decided to find out what would happen if he put several pounds of TNT inside this tank. (Laughter) And that’s the result. Let me move on very quickly to Trinity. I’m afraid we’re running a bit late. This is a 100 foot tower that was set up, the bomb to be placed on the top. The point was to keep its detonation away from the ground so that the ground not contaminate the explosion. Let the explosion take place up 100 feet. Well, here it is. There is the bomb. Not quite assembled yet but sitting atop the tower. Here exercising his curiosity to see the thing is – you can see who that is, can’t you, just from the silhouette. Oppenheimer wouldn’t have missed going up the tower to examine the bomb before it was detonated. Here you have a much more complete assembly of the bomb. These were all detonation devices to detonate in effect a sphere of high explosive. And this was a very complex sphere because it was a sphere which had not simply to explode outward but to create a blast wave that converged spherically upon the material in the centre. It was an extraordinary development that and probably the central one at Los Alamos. Here is the explosion after the first couple of milliseconds. This is the explosion at Trinity. Here it is a second or 2 later. Here is what was left seen from the air. The sand surrounding the tower was turned to a greenish sort of fused glass. And every last bit of it taken up by souvenir seekers presently. The circle you see here, this is where the 100 ton explosion was set off, just ordinary TNT in order to calibrate the instrumentation. And here are the first individuals coming in and looking at the stumps left over from the tower. The tower above had of course been completely evaporated. And this was one of the 4 supports of the tower. There, inevitably again, is the inseparable pair, Oppenheimer and General Groves. This is Victor Weisskopf off on the right. I don’t immediately recognise any of the others. Well, when we saw that - and I happen to have seen that explosion take place. As a theorist I was not welcome at the Trinity site, and so some of us managed to drive cars, which were even pretty scarce then, to the top of a peak, Sandia Peak near Albuquerque, where we had quite a distant view. And I managed by staying there all night and waiting until 5.30 in the morning, which was about 4 hours after we expected the blast to take place. I saw what amounted to a sunrise in the south. A very short time later there was a sunrise in the east. Well, here is what went on in the 3 weeks following the mid-July Trinity test. This was on Tinian Island. This is the implosion bomb, the spherical one. And also, by the way, that was the one tested at the Trinity site. And as you know it worked and that was a cause for celebration by 2 people out of 3 in the Potsdam conference. Truman had been informed about the test immediately. Stalin was probably not informed immediately, but he was surely informed. And there was a bit of a celebration when the war ended, involving of course General Groves and the President of the University of California who formally directed and oversaw the project. But President Sproul had never set foot in the place and never seen, it’s not even clear that he had known about the existence of the project. Oppenheimer, of course, became something of a celebrity. And a year later in the Harvard commencement you had this collection of people: Conant again sitting in the centre, General Marshal who was about to unveil the Marshal plan, General Omar Bradley and here somewhat lost off in the corner is J. Robert Oppenheimer, a Harvard alumnus. And I must say this was quite a reunion seeing him there again. He became something of a celebrity. Now, I don’t know how much further to go with all of this because there are a great many pictures and it’s gotten a bit late for the end of this talk. Maybe if there is a slide machine where we will be talking in the afternoon? It's said I will be with some students, and maybe we can put the slides, the remainder of the slides together. There are a few interesting ones. But they have entirely to do with post-war matters. This is a collection of theorists who gathered at Shelter Island 2 years after the end of the war. But there’s a considerable number of names you would recognise in that. Let me cut it off here in order not to run too substantially over and I’ll see if we can do more this afternoon. Thank you.

Wie geht es Ihnen? Ich bin etwas spät dran, und ich hoffe, Sie sehen es mir nach. Es ist natürlich für die Beschreibung der Ereignisse vor 70 Jahren ein bisschen spät. Ich werde aber versuchen, Ihnen einige meiner Erfahrungen und Erinnerungen aus der Zeit zu vermitteln, als ich erst 18 Jahre alt war. Es war das Jahr 1943. Zunächst möchte ich aber noch ein Stück weiter zurückgehen. Lassen Sie mich sehen, ob ich dieses System zum Laufen bekomme. Können Sie Enrico Fermi sehen? Das war 1938 und er hatte eine ganze Reihe von Experimenten mit Neutronen durchgeführt. Neutronen sind die neutralen Teilchen, die sich im Kern befinden, aber erst wirklich ungefähr im Jahr 1931 entdeckt wurden. Es gab vorher viel Geheimnisvolles. Diese Klärung führte zu einer Vielzahl an Experimenten, die durchgeführt werden konnten. Und Fermi war der Erste unter den Experimentatoren, der entdeckte, was die Neutronen mit dem Kern machten. Er führte Mitte der Dreißigerjahre eine ganze Reihe solcher Experimente durch. Einige seiner letzten durchgeführten Experimente war, einen Neutronenstrahl auf Uran zu richten, dem schwersten bekannten Kern zu der Zeit. Er entdeckte, dass ganz komplexe Dinge passierten, hatte aber keine Zeit, sie zu analysieren, weil er nicht nur den Nobelpreis bekam, sondern dies auch als die Gelegenheit nahm, um mit seiner Familie Italien zu verlassen. Nach einem kurzen Besuch in Stockholm ging er an die Columbia-Universität in New York. Und damit begann ein großer Teil der Geschichte, die ich Ihnen erzählen werde. Er ließ viele Fragen offen, was die Neutronen mit dem Uran machten. Einer der damalig größten Radiochemiker, Otto Hahn, begann das ernsthaft zu untersuchen und entdeckte, dass sehr unterschiedliche Teilchen aus diesen Neutron-Uran-Stößen herauskamen und diese hatten absolut verwirrende chemische Eigenschaften. Als Radiochemiker konnte er verifizieren, dass zumindest mehrere Elemente, die aus diesen Stößen austraten, die gleichen Eigenschaften hatten wie bekannte und viel leichtere Elemente. Die Person, die dieses Problem tatsächlich löste, war zu der Zeit auch ein Flüchtling. Im Jahr 1938 verließ sie Berlin unter Mithilfe von Otto Hahn, ihrem Chef, und ließ sich in Stockholm bei einem ihrer Neffen nieder, Otto Frisch. Diese Frau war Lise Meitner, und sie entwickelte die Theorie, dass es eine Spaltung des Urankerns war, was tatsächlich passierte. Dass zwei Fragmente von ungefähr der Hälfte der Masse des ursprünglichen Urankerns herauskamen. Und es gab viele chemische Konsequenzen, wegen dieser Vielfalt der Kerne, ungefähr in der Mitte des Periodensystems. Nun, diese Idee war in Wirklichkeit ihre - sie wurde nie dafür belohnt -, und führte zu einer Menge an Aktivitäten. Insbesondere Leo Szilard, ein junger Ungar, der schrecklich gerne in die Zukunft dachte, realisierte, dass diese produzierten Kerne ein paar Neutronen zu viel besaßen. Nicht nur würden diese schweren Spaltungsfragmente herauskommen, sondern mehrere Neutronen. Mit anderen Worten, ihm war bewusst, dass es möglich wäre, eine Neutronenkettenreaktion zu erzeugen, und er war über die Möglichkeiten beunruhigt, die sich dadurch eröffneten. Er entschied, dass er mit Franklin Roosevelt, dem Präsidenten der USA, kommunizieren und sicherstellen müsste, dass Amerika die damit verknüpften Gefahren bewusst waren. Er schrieb einen Brief im Auftrag von Albert Einstein an Roosevelt. Und hier trifft er sich im Jahr 1939 mit Einstein an einem Sommerferienort am Ende von Long Island und entwarf den Brief, den Einstein dann gerne unterschrieb. Dieser Brief wurde dann durch einen recht bekannten Bankier Roosevelt übergeben, der ordentlich beeindruckt war. Der ernannte dann die einzige ihm bekannte Person mit technischer Ausbildung, Vannevar Bush, Vorsitzender des Bureau of Standards in Washington, und bat ihn, ein Komitee zu gründen, das sich dieser Sache weiter annehmen sollte. Nun, hier haben sie das Komitee. Wie man sehen kann, war es offensichtlich ein ziemlich freudiges Ereignis für diese Leute, von denen 3 oder 4 Nobelpreisträger waren. In der Mitte befindet sich James Conant, der Präsident der Harvard Universität war, aber eigentlich war er Chemiker. Und nun werde ich nicht die Namen der ehrenwerten Personen durchgehen, aber die Wahrheit ist, dass sie fast nichts machten, außer sich zu vergnügen und noch weitere Komitees zu ernennen. So, das ist, denke ich, wirklich die wahre Einführung in diese Geschichte. Der Mann, der am Rande involviert war, war Kenneth Bainbridge, der in Harvard Massenspektroskopie machte und uns die wahren Massen der verschiedenen Fragmente nannte, die durch die Uranspaltung entstanden und welche dadurch zum ersten Mal richtig verstanden wurde. Bainbridge hatte auch ein Zyklotron gebaut. Hier ist er, stolz auf sein neues Zyklotron. Es muss ungefähr im Jahr 1940 oder 41 gewesen sein, als das Zyklotron fertiggestellt wurde. Und das Interesse an Experimenten mit der Kernspaltung stieg an. Und es gab sogar den Wunsch, noch weitere Experimente durchzuführen. Hier ist jemand, den einige von Ihnen als Robert Wilson erkennen werden. Dort in der Mitte ist Robert Wilson, wie Sie erkennen können. Ich denke, zu der Zeit war er in Princeton, Jahre später in Cornell und schließlich der Direktor des Fermi-Labors in Amerika, dem großen Beschleunigerlabor im mittleren Westen. Aber hier verhandelt er für eine fiktive Organisation namens St. Louis Medical Depot und versucht, das Zyklotron zu bekommen und es irgendwo in den Westen zu transportieren. Wohin sollte es verschickt werden? Nun, viele Menschen kannten bis Ende 1943 eine bestimmte Adresse, diese hier. Das war die einzige Information, die ich bekam, als ich 18 wurde. Ich hatte eine Reihe von Kursen besucht, wie es sie zu der Zeit gab, die meisten Graduiertenkurse, und wurde gebeten, zu dieser Adresse zu gehen. Nun, diese Adresse war Postfach 1663. Und kurz danach bekam ich mit - wissen Sie, ein Postfach in Amerika hat ungefähr die Größe eines Schuhkartons. Und es wäre etwas schwierig gewesen, die zwei Koffer mit Büchern und meiner Habe, die ich dorthin geschickt hatte, aufzunehmen. Aber stellen Sie sich einmal die Schwierigkeiten vor, die Umzugslaster und Frachtlaster voll mit Material aufzunehmen, die alle anderen an diese Adresse geschickt hatten. Wir waren uns noch nicht einmal sicher, dass es in New Mexico war. Dorthin wurden wir nämlich geschickt. In der Tat stellte sich heraus, dass es nicht Santa Fe war, sondern Lamy, ein kleiner hölzerner Bahnhof ungefähr 20 Kilometer von Santa Fe entfernt. Nun, da war ein Mann, der auch wie ich aus dem Zug stieg. Er trug eine Melone und einen marineblauen Mantel und verkündete, sein Name wäre Mr. Newman. Als wir in Santa Fe ankamen, gab es dort ein kleines Büro für das Projekt, und als ich mich eintrug, konnte ich sehen, dass sein Name tatsächlich John von Neumann war. Er war tatsächlich der Autor eines berühmten Buchs, das ich damals gerade las. Er traf jemand, der für alle wie ein Cowboy aussah. Er trug die zwangsläufigen Jeans, ein kariertes Hemd und tatsächlich einen breitrandigen Cowboyhut. Er schien irgendein Cowboy zu sein, der als Fahrer gemietet war. Und dann begann eine Unterhaltung. Eine wirklich bemerkenswerte Unterhaltung zwischen Mr. Newman und diesem Cowboy, der, wie ich später herausfand, tatsächlich Jack Hawking, ein Mitglied der Theoriegruppe und Mathematiker im Labor war. Die Fahrt hoch zum Labor war geografisch bemerkenswert. Dies ist ein etwas später aufgenommenes Bild. Die ursprüngliche Brücke über den Rio Grande, der dort von Norden nach Süden verläuft, war nämlich unterspült – Sie können sie im Hintergrund sehen, das ist die ursprüngliche Brücke. Dies war eine Brücke, die ungefähr ein Jahr später auftauchte, auf dem Weg zu dem 'Hügel', wie wir ihn nannten, der hier hinten zwischen den großen Klippen war. Wir mussten eine Weile nach Norden nach Espanola fahren, um über den Rio Grande zu kommen und dann wieder nach Süden, und da hatten wir diese Aussicht. Es gab immer wieder fantastische Aussichten, während man in die Jemez-Berge hochfuhr. Das ist die Hauptkette, die Sangre-de-Cristo-Berge; man sieht buchstäblich über den Rio Grande zum Talboden. Hier kommen wir zum Eingang des Projektgebiets, wie es damals war. Es befand sich auf einem Plateau, das sich hoch über dem Rio-Grande-Tal befand, auf ungefähr 2100 Metern über dem Meer. Es stellte sich heraus, dass das Plateau von vielen tiefen Schluchten durchzogen war, sodass das Land fast undurchquerbar war, mit Ausnahme der ein oder zwei Straßen, die zu einer nahen Puebloruine führten. Dies ist der Eingang. Als es ein paar Wochen später ein wenig betriebsamer wurde, gab es dort viele Militärpolizisten, die die Papiere von Leuten überprüften, die hinein wollten. Und die vielen Geschichten, die von den Lasterfahrern und von vielen Leuten erzählt wurden, die keine Verantwortung für das Projekt hatten, aber viele absonderliche Dinge erzählten, die sie dort oben auf dem Hügel gesehen hatten. Dies wurde 'das große Haus' genannt. Dort oben gab es die Los Alamos Farmschule für Jungen. Insbesondere mehrere Eltern, deren Söhne Tuberkuloseprobleme hatten, wurden auf diese Schule geschickt, um eine weiterführende Bildung zu erhalten und gleichzeitig die frische, reine Luft von New Mexico zu atmen. Und wenn ich jetzt etwas in die Zukunft springe, es wurde ein Labor. Es wurde ein Labor mit einem eingezäunten Gebiet, das eine sehr beträchtliche Größe hatte. Es gab viele Gebäude, Laborgebäude darin. Und als sie schließlich das viel respektabler gestalteten – so sah das Tor aus, aber das gab es nicht, sagen wir mal, während der ersten 2, 3 Jahre. So wurden die Papiere und das Gepäck überprüft, wenn man das technische Gebiet betrat. Ich habe dieses Bild zufällig bekommen, da der Mann, der dort befragt wird, Robert Marshak ist, einer der Gruppenleiter im Projekt. Nachdem das Projekt schon 1 oder 2 Jahre lief, gab es eine ganze Menge Bauaktivitäten, und viel davon etwas umständlich. Das technische Gebiet begann auf dieser Straßenseite, aber hat schon bald das Gebiet bis zu den Zäunen ausgefüllt. Und sie entschieden, dass sie auf die andere Seite der Straße bauen müssten. Und der einzige Weg, das Problem der Überprüfung der Papiere zu handhaben, war, erhöhte Korridore über die Straße zu bauen, um von einem Teil des technischen Gebiets in ein anders zu kommen. Dies war schließlich dann das E-Gebäude oder der Sitz der Theorieabteilung, von dem ich ein kleiner Teil wurde. Nun, um weiterzumachen, dies war die typische Unterbringung für 4 Familien. Die meisten Leute im Labor waren sehr jung. Es gab Familiengründungen, mit dem Ergebnis, dass beispielsweise das Krankenhaus, bezogen auf die Bevölkerung, eine recht hohe Geburtenrate hatte. Diese jungen Familien produzierten mehr Menschen als nahezu jedes andere Krankenhaus der Armee. (Lachen) Die Unterbringung variierte beträchtlich. Ich mag dieses Bild, nicht nur, weil es zeigt, wie die Leute leben, sondern auch wegen des Waldbrands im Hintergrund. Das Land war sehr trocken. Fast überhaupt kein Wasser, ausgenommen einen sorgfältig gepflegten Teich in der Mitte des Plateaus. Und es war höllisch schwierig, selbst sehr kleine Waldbrände zu löschen. Hier noch mehr Unterkünfte. Hier eine einzigartige Unterkunft, da dort alle unverheirateten Frauen aus dem Labor lebten, etwa 12 oder 14 von ihnen. So sah ein Wohnheimraum aus - nicht meiner, aber man hätte ihn nicht von meinem unterscheiden können. Es war ein Einzelzimmer in einem Behelfsbau, der die Menschen wenigstens vor dem Wetter, dem Regen schützte, und wo wir gelegentlich Wohnheimparties feierten. Dort gab es noch andere Besonderheiten. Viele junge Leute, die eingezogen wurden und denen die Regierung – es gab keine etablierten Wege, das Talent der Leute zu bestimmen, wenn sie zur Armee kamen. Viele Leute mit einer Vielfalt an unterschiedlichen Talenten - vielleicht dachte man, sie hätten Ingenieurkenntnisse oder Ähnliches - wurden nach Los Alamos geschickt, um in diesen Baracken zu leben. Die Aufgaben, die sie hatten, waren für Kriegsaufgaben ziemlich interessant und hielten sie auf Trab. Aber unglücklicherweise glaubte die Armee, dass diese Gruppe von Soldaten die Führung eines Offiziers benötigte. Diese Offiziere waren Menschen, die überhaupt keine technische Ausbildung hatten und keinen Sinn darin sahen, dort zu sein, wenn sie nicht diese Ingenieure etwas exerzieren ließen. Sie weckten sie um 6 Uhr morgens, und sie mussten sich in einer Linie aufstellen und irgendeine Gymnastik oder Exerzierübung durchführen, die für dienlich gehalten wurde. Das führte zu jeder Menge Beschwerden. Diese Männer hatten, soweit es die Armee betraf, sehr sichere und nützliche Stellungen, aber man hat noch nie im Leben so viele Beschwerden gehört. In späteren Jahren gab es dieses kleine Denkmal, das es damals nicht gab. Dort lebte der ursprüngliche Lehrkörper der Los Alamos Farmschule für Jungen. Es gab mehrere solcher Steinhäuser. Nun, von den Leuten, die dort waren, dieser Mann, der die Theorieabteilung leitete, war Hans Bethe. Es war eine bemerkenswerte Wahl, da er unbeschreiblich vielseitig war. Er konnte einem eine auf 2 Stellen genaue Schätzung für wirklich jede irrwitzige Aufgabe geben, die man aus dem Ärmel schüttelte. Es war ein außergewöhnlicher Leiter für die Theorieabteilung. Hier ist der Leiter des gesamten Projekts – Robert Oppenheimer. Er war ebenfalls ein außergewöhnlicher Leiter. Zum einen sah man ihn natürlich nie ohne Zigarette im Mund. Er war ein großartiger Lehrer, hielt aber nichts davon, es irgendjemandem einfach zu machen. Er drückte sich literarisch aus, manchmal fast poetisch, und so wurde er von vielen einfachen Wissenschaftlern bewundert, die von ihm wirklich sehr beeindruckt waren. Wo auch immer er hinging, und er besuchte jeden Teil des Projekts einschließlich aller Experimente, sah man seinen flachen Hut, der eine Art Visitenkarte war. Eine weitere Persönlichkeit, die tatsächlich abwesend war, als ich zuerst im Januar 1944 dort hinkam, war beleidigt weggegangen. Er war gegangen und hatte das Projekt einen Monat lang verlassen, bevor Oppenheimer ihn überredete, wiederzukommen. Und er versprach ihm einen bestimmten Projektteil sozusagen als seinen eigenen Machtbereich. Edward Teller hatte schon auf dem Gebiet der thermonuklearen Reaktionen gearbeitet, mögliche astrophysikalische Reaktionen, und hatte als sein primäres Interesse ausgewählt, irgendeinen Brennprozess zwischen den leichten Wasserstoffatomen herzustellen, insbesondere Deuterium und Tritium. Er war überzeugt, dass man irgendwie die Atombombe als ein Zündholz für das andauernde Feuer verwenden kann. Er glaubte leidenschaftlich daran und meinte, dass er in der ursprünglichen Organisation von Los Alamos ziemlich vernachlässigt worden war. Oppenheimer musste ihn damals überzeugen zurückzukommen, und das tat er dann auch. Sie haben schon viel davon gehört, was er danach gemacht hat. Dies ist Emilio Segrè, Segrè war ein Mitarbeiter Fermis in Rom. Er war bereits in Amerika und hatte eine ungewöhnliche Aufgabe in den Anfängen von Los Alamos: Die Aufgabe war, an einen isolierten Platz in einem der Täler zu gehen, wo der Neutronenuntergrund minimal war, um zu bestimmen, ob das neu geschaffene Element Plutonium, insbesondere in der Form, in der es durch die Atomreaktoren in Chicago erzeugt wurde, und zu bestimmen, ob dieser spezielle Kern in einem beträchtlichen Umfang eine spontane Spaltung zeigte. Das war wichtig, weil spontane Spaltung bedeutete, dass Neutronen überall innerhalb des Materials herumfliegen würden, was immer das Material war, das man benutzte. Und der ursprüngliche Plan, eine Bombe herzustellen, war ein relativ einfacher: Man wollte einen Zylinder, in diesem Fall aus Uran 235, diesen Zylinder in einen ausgehöhlten Zylinder in einer Kugelmasse schießen. Und keine dieser 2 Massen aus Uran 235 wäre über dem kritischen Punkt. Sie würden einzeln keine Kettenreaktion unterstützen. Aber wenn sie verschmolzen, wenn sie zusammengefügt sind, dann würden sie das allerdings. Das war eine schwierige Zeit, während man diese Stücke zusammenbrachte und wenn tatsächlich in der Zeit eine Kettenreaktion startete, wäre das eine vorzeitige Detonation und man bekäme eine viel kleinere Explosion. Im Uran 235 war die spontane Spaltungsrate langsam genug, dort gab es also keine ernste Gefahr. Wenn man eine Kanone benutzte, um das zylindrische Projektil in das hohle Volumen zu schießen, dann hätte man Millisekunden, um es zu tun. Und das war gerade noch möglich mit einer Kanone. Segrè entdeckte aber sehr schnell, dass die spontane Spaltungsrate in Plutonium, das sogar zu der Zeit schneller produziert wurde als Uran 235, das eine Isotopentrennung benötigte, dass die spontane Spaltungsrate und der Neutronenuntergrund bedeuteten, dass man die Plutoniumbombe in Mikrosekunden und nicht Millisekunden zusammenbringen musste. Eine Mikrosekunde ist ein Millionstel einer Sekunde. Und das war das Hauptproblem, mit dem das gesamte Projekt in den Folgejahren zu kämpfen hatte. Nun, hier ist der Rest von Segrès Gruppe. Und nur um Ihnen zu zeigen, wie die Gruppe aussah und wie der Hintergrund und das technische Gebiet aussah. Aber hier im Hintergrund hinter Segrè ist Owen Chamberlain, der unzertrennlich von ihm war. Und die beiden bekamen mehrere Jahre später den Nobelpreis für die Nutzung des Bevatrons in Berkeley für die Identifizierung des Antiprotons. Das ist Martin Deutsch. Hier, fürchte ich, kann ich die anderen Gesichter nicht leicht erkennen. Hier ist eine andere bekannte Person, Dick Feynman. Feynman war nicht nur ein außergewöhnlich kreativer Mathematiker für theoretische Aufgaben, er war auch ein bisschen Clown und Entertainer. Sobald ein paar von den Frauen, die es dort gab, zusammenkamen, sah man, dass sie sich um Feynman scharten, der etwas zum Besten gab. Feynman gab immer den Unterhalter. Und einige von uns hörten seine Geschichten, wie sie von Ralph Leighton, Robert Leightons Sohn, später gesammelt wurden. Es war Leighton, der die Bücher „Sie belieben wohl zu scherzen, Mr. Feynman!“ und die darauffolgenden schrieb. Er war sicherlich einer der markantesten Charaktere in Los Alamos. So haben wir Kolloquien gehört, in Segeltuchstühlen sitzend, die in einer Turnhalle aufgestellt wurden, nachdem sie gründlich nach irgendwelchen versteckten Turnern oder Spionen durchsucht worden war. Und hier ist unser Freund, der polnische Mathematiker, an dessen Namen ich mich im Moment nicht erinnern kann, aber Sie kennen ihn wahrscheinlich besser als ich, der tatsächlich die Aufgabe löste, die 'Super', wie wir sie nannten, zu zünden, die thermonukleare Reaktion der leichten Elemente. Und hier sitzt er auf einer Bank in der Plaza von Santa Fe mit von Neumann und Feynman. Nun, jetzt gehe ich einfach einige Bilder von Personen durch. Dies ist die vielleicht berühmteste Person, die wir dort hatten, er hieß Nicholas Baker. Wenigstens war das der Name, der über die Lautsprecheranlage durchgegeben wurde, weil dort einer der am meisten unausgesprochenen Name Niels Bohr war. Bohr sagte immer etwas, aber er sprach nie sehr viel. Und was auch immer er sagte, konnte man nicht auflösen, weil das Dänische keine Sprache ist, die zu einer hohen Auflösung neigt, und weil er immer seine Pfeife schmauchte. Nun, er zündete ständig Streichhölzer an, nahm einen tiefen Zug des Streichholzrauchs, und zündete ein Streichholz nach dem anderen an. Das setzte sich den gesamten Tag fort. Ich habe hier ein Bild von Bohr mit seinem Sohn Aage, der ihn überall hin begleitete. Dieses Bild kommt nicht aus Los Alamos, es ist typisch für Kopenhagen. Die beiden waren unzertrennlich. Aage, der übrigens auch den Nobelpreis erhielt, aber nicht für das damals effektivste Kernmodell in den frühen 1950er-Jahren, nicht für etwas, was ihn notwendigerweise mit der Bohrfamilie verband. Der Mann, der das Projekt offiziell leitete war Leslie Groves. Er war ein ziemlich korpulenter Mann mit einem militärischen Verstand und erstaunlich wenig Verständnis für die Wissenschaft angesichts der Art des Projekts, das er leitete. Hier ist ein ziemlich idealisiertes Gemälde, das von ihm angefertigt wurde und dort angeschaut werden kann. General Groves und Oppenheimer erschienen oft zusammen. Sie gaben nicht vor, unzertrennlich zu sein. Sie repräsentierten aber die 2 Dinge, die präsent waren: militärische Autorität, die so etwas wie der Antrieb war, der Dinge vorantrieb, und die Intelligenz, die es andererseits lenkte. Was man im Winter wirklich machen konnte, war Skifahren. Es gab viele Skigruppen, ziemlich primitive, es waren normalerweise hölzerne Skis und die einfachsten Stöcke. Diese Gruppe schloss Fermi, Bethe, Weisskopf und ein paar andere ein. Ich will Sie nicht mit all den Namen langweilen. Ich habe dieses Foto mit drin, weil es aus dem Jahr 1931 stammt und viele derselben Menschen zeigt. Sie kannten sich alle. Das ist Heisenberg. Wenn es so ein Projekt gab, und auf irgendeine Weise gab es sicherlich so ein Projekt in Deutschland, dann war Heisenberg die oberste Autorität. Aber neben ihm sitzt Rudolf Peierls, der das Projekt in Großbritannien leitete und eigentlich initiierte. Und im Hintergrund stehen Menschen von vielen anderen Orten. Victor Weisskopf war zu der Zeit ein junger Student. Und Felix Bloch war auch noch ziemlich jung. George Placzek. Ein Mann, der an derselben Art von Dingen in Italien arbeitete war Gian-Carlo Wick im Hintergrund. Diese Leute kannten sich alle. Nun, es war ein großes Projekt. Dies ist die elektromagnetische Trennungsanlage in Tennessee. Hier in Hanford, Washington, ist der Reaktorkomplex, der tatsächlich das Plutonium produzierte. Und damit verbunden gibt es viele Geschichten, aber ich habe keine Zeit dafür. Lassen Sie mich ein paar Geschichten über Los Alamos erzählen, die Sie vermutlich noch nie gehört haben. Es gab die Notwendigkeit, die Explosion, die für den Trinity-Test geplant wurde, zu kalibrieren. Wie würde man diese Explosion kalibrieren? Womit konnte man arbeiten? Nun, die Eingebung war eine weitere Explosion. So, dies ist die Plattform, von der das erzeugt werden würde. Hier sind 100 Tonnen TNT auf einer hölzernen Plattform, die tatsächlich weit vor dem Trinity-Test zur Explosion gebracht wurden, um einfach die Kalibration ihrer Instrumente zu prüfen. Hier ist noch etwas Merkwürdiges: ein Haufen Stahl, eigentlich ein Stahltank. Uns wurde versichert, dass es der größte jemals gebaute Tank war. Es war recht dicker Stahl. Dies war zu der Zeit, als er nach Los Alamos transportiert wurde. Der Grund dafür war, dass die ursprünglichen Tests keine hochexplosiven Stoffe für den Zusammenbau der Bombe involviert hätten, aber man dachte, dass das Material, wie beispielsweise Uran 235 oder Plutonium, so unendlich kostbar wäre und irgendwie gesammelt werden müsste. Man konnte das nicht einfach überall verstreuen. Man musste daher versuchen, was auch immer als Sprengstoff vorlag, um die Bombe zusammenzubauen. Die Idee war, dass man die Bruchstücke sammeln und das Spaltmaterial retten könnte. Also wurde dieser Tank auch prompt 'Jumbo' genannt - zu der Zeit war das der Name eines mystischen Elefanten. Hier wird er nach Los Alamos transportiert. Nun, wurde Jumbo jemals benutzt? Man fand heraus, dass der Sprengstoff, der für die Bombe notwendig war, selbst für diesen Tank etwas zu kraftvoll war. Und daher wurde er nie benutzt. Was auch immer an Kosten und sonst noch damit verbunden war, ihn von Pittsburgh den ganzen Weg bis in die Wüste in New Mexico zu bekommen. Nach dem Krieg - dies ist eine Entwicklung nach dem Krieg - entschied sich jemand herauszufinden, was passieren würde, wenn man mehrere Pfund TNT in den Tank geben würde. Und das ist das Ergebnis. (Lachen) Lassen Sie mich schnell zu Trinity übergehen. Ich fürchte, wir sind ein wenig spät dran. Dies ist ein 33-Meter-Turm, der gebaut wurde, um die Bombe an die Spitze zu setzen. Die Sache war die, die Explosion vom Boden wegzuhalten, damit der Boden nicht die Explosion kontaminierte, die Explosion in einer Höhe von 33 Metern stattfinden zu lassen. Nun, hier ist sie. Dort ist die Bombe. Nicht ganz fertig zusammengebaut, aber schon an der Spitze des Turms. Hier befriedigt er seine Neugier, das Ding zu sehen – Sie können erkennen, wer das ist, nicht wahr, nur von der Silhouette. Oppenheimer hätte es sich nie nehmen lassen, den Turm hochzuklettern, um die Bombe zu inspizieren, bevor sie explodierte. Hier ist ein vollständigerer Zusammenbau der Bombe. Dies waren all die Explosionsvorrichtungen, um eine Kugel an hochexplosiven Stoffen effektiv zu detonieren. Und es war eine sehr komplizierte Kugel, weil die Kugel nicht einfach nach außen explodieren sollte, sondern eine Explosionswelle erzeugen sollte, die kugelförmig nach innen zu dem Material in der Mitte konvergiert. Das war eine außergewöhnliche Entwicklung und vielleicht die wichtigste in Los Alamos. Hier ist die Explosion nach den ersten paar Millisekunden. Das ist die Explosion von Trinity. Hier eine oder zwei Sekunden später. Hier ist das, was übrig geblieben ist, aus der Luft. Der Sand um den Turm herum hatte sich in grünliches, geschmolzenes Glas verwandelt. Und jedes letzte bisschen wurde sofort von Souvenirjägern eingesammelt. Der Kreis, den Sie hier sehen, dort wurden die 100 Tonnen zur Explosion gebracht, nur gewöhnliches TNT, um die Instrumente zu kalibrieren. Und hier die ersten Menschen, die kamen und sich die Stummel ansahen, die vom Turm übrig waren. Der Turm darüber war natürlich komplett verdampft. Und dies war einer der 4 Stützen des Turms. Dort ist wieder die beiden Unzertrennlichen, Oppenheimer und General Groves. Dort ist Victor Weisskopf auf der rechten Seite. Ich kann die anderen gerade nicht erkennen. Nun, als wir das sahen - und ich gehörte zu denen, die die Explosion sahen. Als Theoretiker war ich nicht auf dem Trinity-Gelände willkommen, und so schafften es einige von uns, an Autos zu kommen, die damals ziemlich rar waren, und auf einen Berg zu fahren, Sandia Peak in der Nähe von Albuquerque, wo wir eine weite Sicht hatten. Ich blieb dort die ganze Nacht bis 5.30 Uhr morgens, das war 4 Stunden nach der erwarteten Explosionszeit. Ich sah etwas, das wie ein Sonnenaufgang im Süden war. Kurze Zeit später gab es einen Sonnenaufgang im Osten. Dies passierte in den 3 Wochen, die dem Trinity-Test Mitte Juli folgten. Dies war auf der Insel Tinian. Das ist die Implosionsbombe, die kugelförmige. Und das war auch die, die auf dem Trinity-Gelände getestet wurde. Und wie Sie wissen, funktionierte sie und das war ein Grund zum Feiern für 2 von 3 Leuten auf der Potsdamer Konferenz. Truman wurde sofort über den Test informiert worden. Stalin wurde wahrscheinlich nicht sofort informiert, aber er war sicher informiert. Und es gab eine Feier, nachdem der Krieg zu Ende war, natürlich mit General Groves und dem Präsidenten der Universität von Kalifornien, die formal das Projekt leitete und überwachte. Aber Präsident Sproul hat nie den Ort besucht und ihn nie gesehen; es ist nicht einmal klar, ob er von der Existenz des Projekts gewusst hatte. Oppenheimer wurde natürlich eine Berühmtheit. Und ein Jahr später bei der Harvard-Abschlussfeier gab es diese Versammlung: Conant sitzt wieder in der Mitte, General Marshall, der dabei war, den Marshallplan bekannt zu geben, General Omar Bradley und hier etwas verloren in der Ecke ist J. Robert Oppenheimer, ein Harvard-Alumnus. Und ich muss sagen, es war ganz speziell, ihn dort wieder zu treffen. Er wurde eine Berühmtheit. Nun, ich weiß nicht, wie viel weiter ich gehen soll, weil es noch eine Menge an Bildern gibt und es inzwischen recht spät für das Ende dieses Vortrags ist. Vielleicht, wenn es einen Diaprojektor dort gibt, wo wir am Nachmittag sind. Ich werde dort mit einigen Studenten zusammen sein, und vielleicht können wir die restlichen Dias zusammen anschauen. Es gibt da noch ein paar interessante. Aber sie haben ausschließlich mit Dingen nach dem Krieg zu tun. Dies ist eine Versammlung von Theoretikern, die sich 2 Jahre nach Ende des Krieges auf Shelter Island trafen. Aber es gibt eine beträchtliche Anzahl von Namen, die Sie dort wiedererkennen würden. Lassen Sie mich hier abbrechen, um nicht zu sehr zu überziehen, und dann schauen wir, was wir heute Nachmittag tun können. Vielen Dank.

Roy Glauber on the Trinity test - the first nuclear weapon ever detonated
(00:41:20 - 00:45:37)

 

Only three weeks after this first explosion of an atomic bomb, the bombings of Hiroshima and Nagasaki took place, quickly leading to the end of the war. Despite the joy felt by all that the war was over, many of the scientists who took part in the Manhattan Project regretted the use of nuclear warfare. The research that they had carried out before the war had not only opened the doors to “big science”, but laid an enormous responsibility on their shoulders. Several scientists directly involved in making the bomb set up The Association for Los Alamos Scientists, and stated in their manifesto, “The object of this organization is to promote attainment and use of scientific technological advances in the best interests of humanity.” Not only did some scientists become as recognisable as celebrities in the post-war period, most became advocates for social responsibility and the total abolishment of nuclear weapons. On July 15th, 1955, a decade after the Trinity test, 18 Nobel Laureates signed the Mainau Declaration at the 5th Lindau Nobel Laureate Meeting. One of the sentences reads as follows, “By total military use of weapons feasible today, the earth can be contaminated with radioactivity to such an extent that whole peoples can be annihilated. Neutrals may die thus as well as belligerents.”

But the huge amounts of energy released in nuclear fission could also be put to good use, and with the end of the war, many physicists were diverting their attention towards developing the technology for nuclear power. Sir John Cockcroft, who, along with Ernest Walton, received the Nobel Prize in Physics in 1951 for splitting the atom, was a firm believer in nuclear power as the energy source of the future. Cockcroft became the director of Britain’s first Atomic Energy Research Establishment at Harwell. During his lecture in Lindau in 1962, he stressed that “nuclear power will be essential by the end of the century”:

 

John Cockcroft stressing that nuclear power will be essential by the end of the 20th century
(00:00:42 - 00:02:52)

 

Although nuclear power prospered for three decades after the war, the mental link to nuclear weapons as well as risk of radiation leakage caused widespread concern. Several nuclear reactor accidents, such as the Three Mile Island accident in the United States in 1979, crowned with the Chernobyl disaster in 1986 caused nuclear power to fall out of favour in most industrialised countries. Large costs associated with power plant construction and operation, including the handling and storage of radioactive waste further cemented anti-nuclear viewpoints. Today, there are about 450 nuclear power plants in operation, producing approximately 11% of the world’s electricity, yet many industrialised countries are considering the decommissioning or phasing out of their nuclear power plants. The future for nuclear power may lie with countries in the Middle East, Asia and South America; the United Arab Emirates and Turkey are currently building new nuclear power plants. The impending deficit of conventional fossil fuels, particularly oil, may reignite interest in innovative nuclear energy research and its potential use, despite the perceived risks.

Liquid sunshine and the battle with cancer

The birth of radioactivity marked a new era in medical research. Perceived as a miracle drug, radium quickly moved from laboratory to hospital when it was found that put on or next to a tumour, the radium would cause it to shrink. We now know that ionising radiation damages cancer cells by making many breaks in their DNA, disenabling the DNA repair system.

The discoverers of radioactivity were keen to test the miraculous properties of radium on themselves; after Becquerel developed a burn from carrying a tube of radium in his coat pocket for two weeks, Pierre Curie fixed a sample of radium on his arm for up to ten hours a day and reported the appearance of a scar after 52 days. The uncanny luminous crystals fascinated everyone. The Curies would display glow-in-the-dark test tubes at dinner parties to the delight of friends. Marie Curie even kept a sprinkling of glowing radium salts at her bedside. They did not realise that this ongoing exposure to radioactive elements was what was making them ill – so much so, that they declined to travel to Stockholm to accept their Nobel Prize, blaming their malaise on overall exhaustion from working long hours in dire lab conditions. For decades following the discovery of radioactivity, radioactive elements were added to cosmetics and medicine, or used in paints to make luminous dials on watches, to note one famous example. Many of the workers in the Curies’ lab, as well as Marie Curie herself, and her daughter and son-in-law, the Joliot-Curies, would die of leukemia as a result of years of work around radioactive material. Yet at the same time, radiation therapy for cancer treatment was developed at a relatively brisk pace.
The source of radium is uraninite, formerly known as pitchblende. At the beginning of the 20th century, uraninite quickly became a much sought-after mineral, but was only mined in what was then Joachimsthal, in today’s Czech Republic. The discovery of uranium ores in Colorado in the U.S. in 1913 galvanized the use of radium in cancer therapy. By 1926, the New York Cancer Hospital, now known as the Memorial Sloan Kettering Cancer Centre, possessed 9 grams of radium, more than anywhere else in the world at the time. Gioacchino Failla, who obtained his PhD under the tutelage of Marie Curie in Paris, became the hospital’s Director of Medical Physics and made several marked advances in radiotherapy. The groundwork for much of these first standardised treatments was carried out at the Radium Institute in France. It was here that fractionated radiotherapy, the use of continuous low-dose treatment, as opposed to short, intense treatments, was established.

The two main constituents of radiotherapy are external beam radiotherapy (EBRT) or teletherapy, where X-rays, or gamma-rays produced by a radioactive element, are delivered to the patient from an external source; and internal radiotherapy, or brachytherapy, where the source is placed inside the patient’s body. A basic form of EBRT was placing radium inside a lead box, which was then directed over the patient. Failla was one of the first radiooncologists to use gold tubes filled with radon gas produced by radium, as an early method of brachytherapy. Gold had the advantage over glass that it kept beta-rays from harming the patient’s tissues, but allowed gamma-rays to pass through. The gold tubes were then cut into small pieces, known as seeds, which could be inserted near the cancerous tissue, a practice known as seed implantation, which is still used today. Starting from the 1930s, radium teletherapy and the use of radon seeds in brachytherapy began to be replaced by artificial radioactive isotopes.

The beginnings of nuclear medicine

In 1934, the Joliot-Curies demonstrated that radioactivity was not only limited to natural elements, but was possible to produce artificially. In a series of experiments, they bombarded aluminium with alpha particles from a radium-beryllium source and observed continuous radiation. The alpha particles caused the expulsion of a neutron, creating an isotope of phosphorus. When the Joliot-Curies obtained the Nobel Prize in Chemistry in 1935, “in recognition of their synthesis of new radioactive elements”, they were already aware of the significance of their findings. Frédéric Joliot stated in his Nobel lecture, “(...) large quantities of radio-elements will be required. This will probably become a practical application in medicine.” The age of purifying several grams of radioactive elements from large quantities of minerals was coming to an end.

However, it is George de Hevesy who is distinguished with the title, “the father of nuclear medicine”. Prior to the Joliot-Curies’ work on creating artificial radioactive elements, the Hungarian-born Hevesy, who was then working in Rutherford’s lab in Manchester, came up with the idea that a radioactive substance could be used as an indicator for stable elements. He pursued this notion by studying the solubility of lead and the presence of radium-D, now known to be an isotope of lead, which was physically and chemically inseparable from the stable lead. These studies made way for the use of radioactive tracers in live organisms. Hevesy examined the absorption and distribution of radioactive lead (212Pb) in the broad bean plant, which was followed by a study of radioactive bismuth (210Bi) injected into the muscles of rabbits, a noteworthy step in medical research. Once the Joliot-Curies published their findings on the synthetic formation of an isotope of phosphorus (32P), Hevesy and physician Ole Chievitz successfully used this isotope to monitor its circulation and uptake by animal bones. Hevesy was awarded the Nobel Prize in Chemistry in 1943. Soddy mentioned the importance of radioactive tracers in medicine in Lindau in 1954, noting that, like X-rays, tracers provide “a second sight” to the surgeon:

 

Frederick Soddy emphasising the importance of radioactive tracers in medicine
(00:16:47 - 00:17:28)

 

A significant development in the use of artificial radionuclides came with the construction of the first cyclotron by Ernest Lawrence (Nobel Prize in Physics, 1939) at the University of California in Berkeley. The high-voltage accelerator uses electrical and magnetic fields to greatly increase the speed of protons, which assures a greater probability that bombardment of an atomic nucleus will trigger a nuclear reaction. Upon completion of the first nuclear reactor by Fermi and his team in Chicago in 1942, the commercial use of radionuclides in medical research gained speed. Radioisotopes such as sodium-24 and iodine-131 became standards in diagnostic research, while cobalt-60 and cesium-137 replaced radium and radon gas in cancer radiotherapy. Lawrence’s brother, John Lawrence, perfected the use of radioactive tracers at the Lawrence Berkeley National Laboratory and made other breakthroughs in nuclear medicine with the use of the cyclotron, as recollected by Nobel Laureate Edwin McMillan during his lecture in Lindau in 1977:

 

Edwin McMillan (1977) - Early Days at the Lawrence Laboratory

Ladies and gentlemen, I would like to start with a little explanation. The talk that I am about to give you was originally prepared as part of a celebration of the 45th anniversary of the Lawrence Berkeley laboratory that was held last year and it was intended to be a brief history in what one might call an anecdotal form. That is it touches somewhat on the light side of things. It deals a little bit with the scientific history of the laboratory but largely it deals with the people and the things that happened. So with that small explanation I will begin the talk as I gave it. This will be a multimedia presentation. I will start with a more or less connected discourse and finish with a slide show. When I speak of the early days I include only the period up to the end of 1940. By then, many people in the United States had become deeply concerned over the war in Europe. Some had left the laboratory for war work and soon the laboratory itself became involved in war work. One major peace time project was started in 1940, the 184-inch cyclotron. But it did not get back to its original purpose until after the war. The hill above the big C, I should explain that, in Berkeley there is a hill behind the town, there is a big letter C for California put there by the students and I’m referring to that. The hill above the big C was chosen for the site and by the end of 1940 the magnet foundation was completed and the bottom yoke was in place. This started the first expansion of the laboratory off the campus, the stage and growth belonging to a later period beyond what I’m covering here. The radiation laboratory was the personal creation of Ernest Lawrence. It was his idea, he got the financial support, he pulled together the equipment and drew the people and of course he supplied the key idea, the cyclotron. Many other people helped in essential ways. I could name President Sproul of the university, Leonard Fuller of the federal telegraph company in the university who arranged the gift of a large magnet for the 27 and 37-inch cyclotrons. Frederick Cottrell and Howard Poillon of the research corporation. And Francis Garvan of the chemical foundation who looked with favour on Ernest’s request for grants. Raymond Birge who became chairman of the physics department in 1932. Donald Cooksey from Yale, Stan Livingston and many others. But it was Lawrence’s laboratory. Those of us who were there in the early days remember that Ernest was always The Boss, with a capital T and a capital B, that was a very important distinction. He could be very rough on people if he felt they were not giving their utmost efforts, but he made up for this by his generosity in giving credit and ensuring ideas. I never met Rutherford, but I’ve been told that he had the same kind of character, with an important difference, Rutherford favoured the individual researcher working with simple apparatus. Lawrence believed in effort so large that team work was necessary. In the very beginning there was a penalty for this. The drive for greater energy in beam current was so frantic that people hardly had time to think. So important discoveries were missed and some mistakes were made. But this phase soon passed. On the whole I think Lawrence was right. The rapid development of the cyclotron was more important to nuclear science than the question of who made which discovery. The laboratory was started in 1931. And when I came to Berkeley near the end of 1932 it was in full swing. There was not only the 27-inch cyclotron giving protons of around 2 MeV, but also the Sloan x-ray tube on which great hopes were placed for cancer treatment. And a couple of linear accelerators of the Widerøe type which were built and operated by Dave Sloan, West Coates and Bernard Kinsey. The Sloan x-ray tube was used clinically for many years but the linear accelerator concept fell by the wayside, waiting to be revived by new ideas coming from war time radar developments. It was certainly a busy place day and night, especially when Ernest was there, which was most of the time. I started my research in Le Conte Hall, that is the physics building at the University of California Berkeley. I started my research in Le Conte Hall on a molecular beam problem but dropped that when the result I was seeking was obtained elsewhere and entered the exciting world of the radiation laboratory in the spring of 1934. Stan Livingston, the cyclotron expert, and Telesio Lucci, a retired commander in the Italian navy, who was a beloved general helper and factotum, gave me sage council on how to comport myself. As my previous experience had been in working alone and I needed to learn the art of team work. This was not obviously easy since no one was routinely coordinating the various tasks needed to keep the cyclotron going and there were the twin dangers of neglecting what one should do or getting in the way trying to do something that someone else should do. Robert Oppenheimer was the chief theoretical advisor for the laboratory and he suggested that I study the gamma rays produced by proton and deuteron bombardment of light elements. This turned out to be an important experiment because I found a 5½ MeV gamma ray from fluorine bombarded with protons with which I could check Bethe and Heitler's new theory of gamma absorption by pair production. The chief line of research going on then was the study of nuclear reactions by observing the protons and alpha particles which are emitted during bombardment. These were detected by thin ionisation chamber connected to a linear amplifier device not suited for observing gamma rays. Geiger counters were considered unreliable. Stan Livingston tells in a paper presented in Texas in 1967, what happened on February 24 in 1934 when the laboratory learned of the Joliot-Curie discovery of artificial radioactivity. They were using a Geiger point counter, a device that now seems as exotic as the cohere, to count alpha particles. It was not the familiar cylindrical Geiger Muller counter. The cyclotron oscillator and the counter circuit were turned on and off by the two poles of the double pole knife switch for convenience and timing. Within half an hour the switching arrangement was changed so that the counter could be turned on while the cyclotron was off. The counter voltage was raised so that it would count beta particles. The internal target wheel was rotated to bring a carbon target into the beam. And the activity of nitrogen 13 was there, produced by a different reaction than that used by its discoverers. The failure to see this activity first was a blow to the laboratory and there was a natural reaction against all Geiger counters. So the first thing I did when I entered the laboratory was to go to Pasadena to learn from Charlie Lauritsen himself how to make quartz fibre electroscopes. I had my first Lauritsen electroscope which was mounted in a lead ball chamber for detecting gamma rays inside the laboratory for only a few days when Malcolm Henderson came to me in the middle of May with the news of the discovery of neutron induced radioactivity in Rome and he wanted to use my electroscope to look at some of these activities. It took only a short while to make a new chamber out of a tin can with a thin aluminium window and the tin can version of the Lauritsen electroscope became a valuable instrument for observing beta rays. Jack Livingood made one like it which he used in a monumental survey with Seaborg and others of activities produced in many elements by deuteron bombardment which resulted in a rate of discovery of radio isotopes that was comparable to that of Rome following the Fermi’s first neutron induced activity. Some of those that they found became very important in medical and other applications, like iodine-131, iron-59, cobalt-60 and technetium 99m. There was a great surge of activity in the field of artificial radioactivity. The names involved are too many to list completely. Stan Livingston and I found a radioactive form of oxygen and Lawrence found sodium-24 which created a sensation because very strong samples could be made. Once Lawrence had the cyclotron crews working around the clock to make a whole curie for demonstration, that was a tough job. Jackson Laslett found sodium-22, which was the longest life artificial activity known at the time but was soon to be surpassed. Martin Kamen and Sam Ruben found carbon-14, probably the most important radioactive isotope of all and so on. Also new types of activities were discovered. Van Voorhis found that copper-64 could decay by emitting either negative or positive electrons, which was the first known example of that kind of radioactive decay. And Luis Alvarez found the first case of decay by orbital electron capture, which is now a well-known process. Among the new activities were some that had atomic numbers differing from that of any known element and were therefore new elements. First of these was found by Emilio Segré and Carlo Perrier in 1937. They worked in Palermo with a piece of molybdenum that had been on the leading edge of the deflector plate in the cyclotron where it got a lot of bombardment, and which Segré had taken back with him after a visit in the summer of 1936. In it they found element 43 which they named technetium after the Greek word for ‘artificial’, as it was the first artificially produced element. Next was element 85 called astatine for the Greek word for ‘unstable’, found by Segré, Dale Corson and Ken MacKenzie in 1940. A little later in that same year of 1940, Phil Abelson, who had been a graduate student with Lawrence, came back to Berkeley for a short visit and supplied the missing link in the chemical identification of an activity induced in uranium by neutron bombardment which had been puzzling me for some time, it was mentioned in the introduction. This was, as I’d expected, the first transuranium element. I named it neptunium after the planet Neptune, just as uranium had been named after the planet Uranus. After Phil Abelson left, I continued the work trying also the deuteron bombardment of uranium which produced different isotopes of neptunium than the neutron bombardment and found alpha particle activity in the neptunium samples, which suggested the presence of the next transuranium element. Because after the beta particle you get, the next step would naturally be an alpha particle and that leads one to think that that was the next one. I did some chemical separation, showing that the alpha activity did not belong to uranium or neptunium, but did not complete this investigation because I was persuaded by Ernest Lawrence to go to the Massachusetts Institute of Technology for a few weeks to help set up a new laboratory for developing microwave radar. It was not called radar then, that word was coined later, but we did work on radar. As a cover, the new laboratory was called the radiation laboratory. So there were two rad labs, that was sometimes a source of confusion. I left Berkeley by train for Boston on November 11th 1940. On November 28 Glenn Seaborg wrote me that Art Wall had been making some strong neptunium samples and said: and it would please me very much if you could continue the work on 93 and 94”. Now, in parenthesis, the ‘some time’ stretched out to 5 years before I came back to stay. I never did believe Ernest’s estimate of a few weeks. That’s the end of parenthesis. On March 8th 1941 Glenn wrote to me describing the final chemical proof that the alpha activity belonged to the next element up the periodic table, plutonium. In this correspondence, we did not use the names for the new elements which were not yet official, but referred to 93 and 94, and the March letter was marked ‘confidential’. You see secrecy was already creeping into nuclear research and after that secrecy became absolute and none of these things were published for a long time. Luis Alvarez came from Chicago in 1936 with a lot of clever ideas. He was the originator of the method of getting what is effectively a beam of very slow neutrons by pulsing the cyclotron and getting the detector so that it is only sensitive at some chosen time after the pulse of neutrons has been emitted. With Ken Pitzer he used this method in an investigation of neutron scattering by the two kinds of molecular hydrogen, ortho- and parahydrogen. And with Felix Bloch of Stanford he made the first measurement of the magnetic moment of the neutron. One of the questions at that time was the relative stability of the nuclei hydrogen-3, called tritium, and helium-3, both of which had been observed by Mark Oliphant at the Cavendish laboratory, the products of the bombardment of deuterons by deuterons. Alvarez and Bob Conrad first showed that helium-3 is the stable one by detecting it in atmospheric helium using the cyclotron as a mass spectrometer. Then, knowing that hydrogen-3 must emit beta particles, they looked for activity in deuterium gas bombarded by deuterons and found the activity, establishing tritium as a radioactive isotope. Gilbert Lewis at the university of California, Berkeley Chemistry Department, played a very important role in the laboratory’s history. As soon as the discovery of deuterium was announced, he set up equipment to make heavy water by electrolysis and furnished a sample of heavy water to the laboratory. And in March 1933, the first beam of deuterons was produced by the cyclotron. That was a very important step ... From then on, a major part of the work was with deuterons, which are much more prolific and produce nuclear reactions that are protons or alpha particles. And I say prolific, I mean, firstly the cross sections are larger so that you get more abundant reactions, you also get a greater variety of reactions because the deuteron contains two nucleons and you get more variety also. Lewis, like many associated with the laboratory, was a colourful character, he liked to tell how he fed some of his first heavy water to a fly and it rolled over on its back and winked at him. The second anecdote I have here I heard myself, one day at lunch at the faculty club, Lewis heard some professors in the Department of Education arguing about whether children should be taught to add a column of figures from the top down or from the bottom up. Gilbert Lewis said: I could go on and on. There were many visitors to the laboratory who stayed and worked there for considerable periods of time, like Jim Cork from Michigan, Jerry Kruger from Illinois, Lorenzo Emo, a Count from Italy, Harold Walke and Don Hurst from the Rutherford Laboratory, Wolfgang Gentner from Germany, Maurice Nahmias from France,Sten von Friesen from Sweden, Ryokichi Sagane from Japan and Basanti Nag from India. The working visitors were very important to the laboratory. They not only contributed to the research program but they carried back the cyclotron art to their own institutions. Lawrence actively promoted this diffusion of knowledge and Don Cooksey wrote what we call ‘Cook Books’ of cyclotron lore which were mailed to innocent institutions and many people from the Berkeley laboratory went out to help design and build cyclotrons elsewhere. Milton White went to Princeton, Henry Newson to Chicago, Hugh Paxton to Joliot laboratory in Paris, Jackson Laslett to Copenhagen and Reg Richardson and Bob Thornton to Michigan. So the ability, the knowledge of building cyclotrons was rapidly diffused. And I think this diffusion, if we might call technological knowledge, was very important in the advancement of nuclear science in that time, we’re talking about the ‘30s now. Many of the physicists took part in the running and maintenance of the cyclotron. There were regular crews assigned to this task. I remember being on the owl crew for a while, which did not bother me as I was then a single man with rather nocturnal habits, but it was hard on some of the others I remember. But if anything went wrong, we had to pull the cyclotron apart and try to fix it. The greatest problems were vacuum leaks and the burn out of filaments in the ion source which was inside the cyclotron tank and also in the demandable oscillator tubes that had been built by Dave Sloan. When the ion source filament went out, the vacuum tank of the cyclotron had to be rolled out of the magnet gap, then the waxed joint between the lid and the tank broken and the lid removed, the filament replaced and it all had to be put back together again and the joints sealed up and the air pumped out and so on. Physicists did more than just operate the machine. For example Art Snell and Ken MacKenzie built oscillators, Bob Wilson made the first theoretical study of orbit stability and I designed the control system for the 60-inch cyclotron, I was even doubling as an electrical engineer for a while. This was in 1938 and a new concrete building, Crocker Laboratory, was under construction to house the new larger cyclotron. The laboratory was now starting to expand. Bill Brobeck came in 1937 as the first professional engineer hired by the laboratory, that created a real revolution. No more wax joints that leaked, no more equipment that fell apart in the middle of an important experiment or at least less than before. The string and sealing wax school of physics still has a nostalgic appeal to some old timers like myself. But it’s not suited to large efforts where many people are depending on the reliability of apparatus. Win Salsbury and Bill Baker, both electronic geniuses, took over the designing and building of oscillators and other electronic equipment. Charlie Litton came for a while and taught us many techniques in radio frequency engineering. He had a small company in Redwood city which he later sold to some entrepreneurs from Texas who used it as a nucleus for the giant conglomerate called Litton Industries. Charlie retired to Grass Valley where he spent the rest of his life happily working on various inventions. Interest in biomedical applications started very early, Ernest’s brother John is a physician and Ernest always had an attraction to the field of medicine. I have already spoken about the Sloan x-ray tomb which went into medical use in 1934. The next year John came to Berkeley, John Lawrence that is, John came to Berkeley for the summer and made the first observations of the effects of neutron rays on living organism. Finding the effects greater than those of other forms of radiation and therefore very interesting. And in 1936 he came to stay. Paul Aebersold became the chief physicist for the biomedical group. Making the arrangements for irradiation and measuring the dosage. The first cancer patient was treated in September 1938, with sufficiently encouraging results that the Crocker laboratory was devoted to medical research, although the physicists and chemists got to use it too. There were working visitors in the biomedical field also. Frank Exner from New York, Isidor Lampe from Utah, Raymond Zirkle from Pennsylvania, Al Marshak, Lowell Erf, John Larkin, and many others. Doctor Joseph Hamilton had a separate group studying the distribution of radio isotopes administered to animals and humans. To the smells of hot oil from the cyclotron were added those of animal colonies. As Laslett said in his ‘cyclotron alphabet’, “M stands for mice whose smell makes us moan”. We went through the WPA period. It was during the great depression and the WPA was a scheme by which unemployed people were hired by the government and assigned to governmental bodies or other institutions to perform useful work. This stood for Works Progress Administration, WPA. I have a 1934 letter from Lawrence to the university office, handling this program, requesting for a period of 1 month Some of those who came on this program were real characters. I remember particularly Murray Rosenthal who was an amateur magician, a Swedish draftsman named Hallgren who was so profane that we tried to keep him away from Don Cooksey who objected to his language. And a man who had been with the telephone company, who was very distinguished looking and he liked to go around checking the strength of soldered joints by pulling at the wires with a button hook. Some who were only temporarily down on their luck stayed on and became valuable members of the laboratory staff. Some idea of the financial scale at that time was given by the cost estimate made by Wally Reynolds in 1931 for the installation of the 80 ton magnet. This includes moving the magnet from San Francisco and setting it in place, 4 transformers, a 50 kilowatt motor generator set, a 10 ton crane, concrete peers, labour engineering and contingencies, all for $5.300. It is hard to convey the atmosphere of that time. The world was in a deep depression, there was a general strike in San Francisco in 1934. Some people on the campus took sides during this strike and friendships were broken over this. There was a lot of leftist agitation which later had dire consequences for many scientists. There was not much money around. For seven months, between the end of my fellowship and my appointment to the faculty as instructor, I was a research associate without pay. But we all managed somehow and the laboratory kept going. Lawrence was the driving force and the spirits inside the laboratory were kept high by the excitement of discovery. There was very little organisation, Lawrence was the boss and that seemed to be enough. What a change has taken place since then. The eager youth has grown into an adult with increased powers and problems that come with maturity. So that’s the end of the more or less connected discourse and now comes the slide show. And we used half our time up more or less, so we’ll go on with the slides, could I have the first slide. This is Ernest Lawrence, taken on September 19, 1930, just after he had given the first scientific paper on the cyclotron at a meeting of the National Academy of Sciences on the Berkeley campus. He is holding a glass, brass and wax apparatus with which he and Neils Edlefsen had obtained evidence of ion resonances in a magnetic field encouraging Ernest to go on with the development of the cyclotron idea. From his expression you can see that he has hopes for the future. You see this was in September 1930 and this was before the radiation laboratory was started, but that little apparatus that Lawrence is holding was the thing that gave the first evidence that the cyclotron might work and encouraged the whole thing to go on. Now slide 2. Here are Stan Livingston and Ernest Lawrence standing beside the big magnet in the shop of the Pelton Water Wheel company in San Francisco. This magnet had been built by the Federal Telegraph Company of Palo Alto for use as part of a Poulsen-arc radio transmitter ordered by the Chinese government. But it was never delivered and Leonard Fuller, who was the vice President of the Federal Telegraph Company in Palo Alto, also at the same time chairman of the department of electrical engineering in Berkeley, he arranged for that magnet to be given to the university for the researchers of Lawrence. And, as I said, there it is being converted into a cyclotron magnet, the bottom pole was removed and new poles were built. The core and poles of the magnet had to be changed before it could be used as a cyclotron magnet and that is being done here in late 1931. Stan Livingston made the first cyclotron that worked. After that little model that we showed in the last picture, Livingston took over and built the next model and he made one that really did work and he found a beam of 80,000 electron volt hydrogen, molecular ions. And we heard about hydrogen molecular ions earlier, they’re the simplest molecule, so the first thing accelerated in a cyclotron. He found those on January 2, 1931 in a 4-inch cyclotron. Then he made an 11-inch cyclotron with which in 1932 Milt White confirmed the lithium disintegration results of Cockcroft and Walton. This work was done in Le Conte Hall, but the big magnet needed a larger place to house it. As you all know, Stan was one of the discoverers or inventors of strong focusing without which most of high energy physics could not have been done. So Lawrence invented the cyclotron, Livingston made one work, the first one work and they’re really the creators of this whole business. Slide 3. This shows the old radiation laboratory. It had been a civil engineering testing laboratory, was scheduled to be torn down, but Ernest persuaded President Sproul, the President Sproul of the university, not of the United States. Of course in a university town, as you all know, in the United States, anyway when you say ‘President’ you’ll always mean the President of the university, not of the United States. Ernest persuaded President Sproul to let him have it for his experiments. This occurred on August 26, 1931 in President Sproul’s office. At that time Ernest had the promise of financial support and a formal offer of the magnet, so if one wants to choose a day for a birthday, this could be it. Early in 1932, the name ‘Radiation Laboratory’ was painted on the doors. You can’t see that in that picture, but around the door, the outside doors all said ‘Radiation Laboratory’, way back then in 1932. The magnet was installed in January 1932 and the 27-inch cyclotron, first operated in June of that year ’32. Six years later the magnet poles were enlarged and the 37-inch cyclotron was installed. In a cool record, for November 10, 1937, I found the following form by Martin Kamen and of course Martin Kamen was a man who with Sam Ruben discovered carbon-14. And he also liked to write poetry of this type: The cyclotron is a noble beast, It runs the best when you expect it least, Of all the pleasures known to man, The greatest is a good tight can. And the can he meant the vacuum tank, that’s what we called it. And you remember what I said about the misery of leaks, because it was really, it was misery, you’d spend the whole night, you know trying to find a leak, and then you finally get it fixed and the wax would suck in and you’d have to start all over again. In this building which you see here, there was a large room for the cyclotron and its controls. There was an open court for transformers and switchgear. There was a machine shop and some office space. Whenever there was trouble with the commutator or the generator that supplied the magnet current, I was called in to fix it, I was considered an expert at soldering with a torch in those days. One time I remember that Franz Kurie, when he was starting the motor generator, threw in the switches in the wrong order and blew out the lights in all of Berkeley. That building was the scene of frustration and elation, human as well as scientific drama. Many anecdotes have been told about happenings there, like the times that Ernest Lawrence fired Bill Baker and another occasion he fired Bob Wilson, only to recant and take them back again. But on the whole relations were remarkably harmonious considering the many different temperaments of the people. After the war, the first test of the synchrocyclotron principle were done here in this building and in it Melvin Calvin did his pioneer work on the carbon cycle and photosynthesis. Now we have slide 4. That’s another view of that same building, taken in 1959. It’s being demolished, the demolition proceeding toward you in the last view, in the direction which would have been towards you in the last view, and not much is left of the building, I am standing there, that’s me, sadly viewing the end of an era. Later Crocker Laboratory had to go, too. The chemistry department needed space for more buildings. So that was indeed the end of an era because it was in that old building that the whole business of nuclear physics with cyclotrons, with accelerators, circular accelerators got started. Slide 5. This is the 27-inch cyclotron in 1932. Vacuum chamber you see in the middle, sits between the poles and the magnet and it’s all covered with wax, everything was waxed together in those days. The stow pipe going up in front, that pipe has a wire strung down the middle which connects or carries the collected beam current to a galvanometer on the control table which is out of the picture on the left. And sticking out toward you in the front of the vacuum chamber is the linear amplifier built by Malcolm Henderson which was used to count protons and alpha particles. The magnet windings were cooled by oil in those big circular tanks, they were full of oil that was circulated by a pump. And there was always oil all over everything. One time Luis Alvarez neglected to close a valve after turning off the oil circulating pump and the whole tank of oil ran over and went through the cracks in the floor into the basement. I remember that was a very dramatic incident by a Nobel Prize winner. Slide 6. This shows Ernest at the other side of the cyclotron, also in 1932, that photo has its own date that’s written on that hydrogen tank in front, you can’t read it here but in the original you can read it. Behind Ernest is the oscillator that supplied high frequency power to the cyclotron. You can see that in this picture it uses a commercial vacuum tube but these were expensive and so for quite a while we used home made tubes designed by Dave Sloan and which were demountable, they had a wax joint so that you could take them apart and change filaments. Ernest is recognised as one of the worlds great experimental physicists, but he was not particular adept with his hands and contributed his share in the breakage of apparatus, as did all of us. When some delicate task was to be done, he would turn to someone else and say Now, next slide, 7. This is Dave Sloan with his x-ray tomb which was essentially a test coil and a vacuum tank and was actually, this x-ray tomb was actually the first apparatus installed in that building, you see as I told you the big magnet didn’t go in until ’32 but this went in in ’31. Dave was very important to the laboratory, he could build anything and was full of ingenious ideas. He built large oil diffusion pumps when such items were not obtainable commercially and made the mountable oscillator tubes in which the filaments could be changed by taking apart a wax joint. One time he tried to make a diffusion pump using bismuth vapour, this did not work very well but it was an interesting idea. He was still active at physics international working with high current accelerators, a natural continuation of what he did here. Next slide. Here is another side of the laboratory, the machine shop in the old radiation laboratory. Without shops the laboratory could not operate. We used our own shop and also the shop in Le Conte Hall, the physics department shop and large jobs were sent out to commercial shops. In this view on the left is George Krause and the right is Eric Lehman, working on a cyclotron tank, or at least looking as if they were contemplating working on it. And sitting in front are Don Cooksey, who was very important as a general helper in the laboratory and organiser. Sitting in front are Don Cooksey who made the shops one of his primary concerns and Jack Livingood, the great hunter of radio isotopes. That’s Livingood in the corner. Three men who worked in that shop in the early days, Don Stallings, Jack Kroll and Paul Wells, are still with the laboratory. Now next is slide 9. This shows Art Snell, Franz Kurie and Bernard Kinsey who were, I think, in the Strawberry Canyon pool when this picture was taken, I was almost tempted to say they’re at the Bad Schachen pool but the background is not exactly right for that and the time is not right for that either. Art Snell came from Montreal in 1934, later went to Chicago and is now at Oak Ridge. He was famous as the poet laureate of the laboratory, he would make limericks up for all occasions. When Lawrence was awarded the Nobel Prize in 1939 he sent a wire that said: He also built an oscillator and he discovered radioactive argon, among other things. Franz Kurie, the man in the middle, Franz Kurie seems to be giving a Tarzan yell, but he was actually a very gentle person. He introduced the cloud chamber technique into the laboratory. He made measurements of the energy distribution of beta rays and invented a method of presenting the data for beta ray distributions that made it easy to determine the upper limit of the energy. This is now known as the Kurie plot and has been widely used. In an investigation of the disintegration of nitrogen by neutrons he found some unusual tracks which could be interpreted as being due to the capture of slow neutrons and the emission of protons resulting in the formation of carbon-14. This observation of Kurie’s served as a clue in finding the best method of making carbon 14, which as you might guess from what I have said, is the capture of small neutrons by nitrogen. For quite a long time I had a bottle of ammonium nitrate, sitting near the cyclotron target, hoping eventually to separate out carbon and see if it was active. This bottle got knocked over and broken and I never put one back. People considered it to be a nuisance and some were even afraid that it might explode. There had been some large explosions involving ammonium nitrate. But I don’t think a small laboratory bottle was that dangerous. When carbon-14 was eventually identified and carbon bombarded by deuterons, Kamen and Ruben then tried neutrons on nitrogen and they never went back to the carbon bombardments in which the yields were smaller and the active carbon was diluted by all the ordinary carbon. Franz Kurie later was the director of the US navy radio and sound laboratory in San Diego. And the third man, Bernard Kinsey was a commonwealth fellow from England. He built a linier accelerator for lithium ions. There are many stories about Bernard, he had a high temper and a very complicated and colourful form of swearing, really a high art. He was here at this celebration and perhaps he might be persuaded to give us, not this celebration, but the one where I gave this first. He was here at this celebration and perhaps he might be persuaded to give us an example. There was another commonwealth fellow at the university named Brown who was probably the laziest man I ever knew, I don’t think he ever did anything. When I saw him around the faculty club where I was living at the time, he obviously was not in the laboratory, Ernest would have thrown him out. Now we come to slide 10. This is the Crocker laboratory that I mentioned earlier. Old radiation laboratory is off to the right, across an alley and the 60-inch cyclotron resided in the high bay at the rear of that building. This was called the medical cyclotron but, as I have said, others used it. It went into operation in 1939, giving deuterons of about 9 million electron volts. Under the supervision of Doctor Joseph Hamilton it was used extensively for making radio isotopes for medical and tracer uses. Now the next slide. Here is the 60-inch cyclotron, Don Cooksey and Ken Green. You see that it’s much neater looking than the earlier cyclotrons. Bill Brobeck was our first engineer, he had his influence. The structure projecting at the right was a pair of tanks that held the dee stems which formed a resonant system. The oscillators were on the balcony at the right. You’ll notice a coil of heavy cable at the top, that coil stuff up there, this carried high voltage to the deflector plate from the rectifier built by Ed Lofgren. The reason for the coil is that high voltage cables usually fail at the ends and are very hard to splice. So the coil gave plenty of slack for making repairs. Next slide. This is looking through the window into the control room of the 60-inch cyclotron, you see Bill Brobeck, our engineer on the left and Bob Wilson smoking his pipe, Bob Wilson of course now is the director of the Fermi laboratory, Batavia, Illinois. And then there’s Ernest Lawrence and a couple of other characters. One of them is me and the one behind I don’t remember who that was. This temporary set up that mars the neatness of the control table was a bread board model of an automatic magnet current regulator that was being tested. Next slide. This shows a group of people, the man on the left, I don’t know who that is. Then comes Ernest Lawrence holding the manuscript. Dale Corson, physicist who is now President of Cornel university. Winfield Salisbury our electronic genius and Luis Alvarez who is one of the laureates. Corson participated in the discovery of astatine and is now the President of Cornel university. Salisbury has had a distinguished career in industry and the academic world since leaving the laboratory. He made very valuable contributions to radar counter measures during the war. Luis, as you know, went on to win the Nobel Prize in physics and so on. Next slide. This shows John Lawrence, brother of Ernest Lawrence, taken in 1936 with rows of mouse cages in the background which is a proper setting for a biomedical researcher. I will not say anymore about the biological medical research which will be covered by another speaker on the program this was on. Slide 15. Again there are mouse cages, this time with mice in them, but the date is later, 1939, and the person is different, Doctor Joseph Hamilton. Doctor Hamilton had a set up in Crocker laboratory where he worked with radio isotopes on medical and biological studies. His work was quite pioneer work, showing the paths of the heavy elements in animals and in man. Joe’s lunch table at the faculty club was noted for the interesting conversations on many subjects. I remember that he had a special table, a sort of a ‘stammtisch’ and I used to sit there and we discussed everything. Next. All was not hard work, we had fun, too. There was an Italian restaurant called Di Biasi’s, in a small town near Berkeley and the Di Biasi parties were famous yearly affairs in the laboratory. And that was when we would let off steam and have fun. Here is Paul Aebersold who is the man who was the physicist who worked with the biologist and the medical people in the setting up, measuring of dosages and setting up of patients and so on. The one holding the cake there, Paul Aebersold had an irrepressible sense of humour and was always the master of ceremonies. This party in 1939 was in celebration of the 60-inch cyclotron and Paul was presenting a cake in the shape of a cyclotron with the words "8 billion volts or bust". That was supposed to be a wild exaggeration but the Bevatron has not been invented yet. You remember it was just a few years later that we had 6 billion volts, which was almost this number given then as an impossible exaggeration. Lawrence is on the left foreground and the man in the middle foreground, Sten von Friesen, one of our visitors from Sweden. Next Slide. Also at the same party, the man on the left is Martin Kamen, looking puzzled about something, then there’s Sten von Friesen next, Bob Cornog, who worked with Alvarez and the discovery of hydrogen-3. Then there’s Ken MacKenzie is on the left background. It’s a little dark for this, on the right there in the background, Mrs Lawrence, Ernest’s wife, flanked by two distinguished visitors, Vannevar Bush on our left and Alfred Loomis on our right. Alfred was a great friend of Ernest and the laboratory and helped in many ways. Next slide. That’s Lorenzo Emo Capodilista who was the count from Italy that I mentioned, who was one of the colourful characters of the early days. He came to the laboratory in 1935 and stayed several years. He did not use the last name, Capodilista, which means 'head of the list', which his apparently a name of very great antiquity in Italy, he was a very fine fellow. Slide 19. This is Charlie Litton, the man who came and helped us in many technological aspects and whose name was used in connection with Litton industries. He was working with a glass slade which he made himself, the main thing, his original product was glass slades like that. Next slide. This is Maurice Nahmias from Joliot-Curie’s laboratory in France, posing with the vacuum chamber for the 37-inch cyclotron in 1937. Next slide. That’s Henry Newson, who came from Chicago in 1934, the PhD in chemistry, I think he fits in very well with this group here. Came as a PhD in chemistry but became a physicist, he did some very ingenious experiments using recoil of artificially produced radioactive nuclei. This picture was taken in 1938. Next slide. This is Ernest and Molly Lawrence with their first two children, Eric and Margaret, they ended up having six but this was the beginning. This was taken on the steps of the Crocker lab in 1939. Next slide. This is Ernest Lawrence writing the script for a movie about his Nobel Prize in 1939, he’s simply using the fender of a car as a desk there and writing the script. Now let’s go on to next slide. That is Lee de Forest, the inventor, the man who put the grid in the vacuum tomb, who visited the laboratory. We had many distinguished visitors in the laboratory and I included two shots, there’s de Forest. Now I can show you the next slide, which is Diego Rivera with Lawrence. Diego Rivera of course was the Mexican mural painter and he came to San Francisco and painted a mural on the wall of one of the buildings there. And I remember going over and watching him working on it. We’re coming to the end. Next slide. That will do, that should be 90 degrees around but it will do. That’s one of the original 1934 Lauritsen electroscopes that I built when I first came to the laboratory in ’34 and used for that early work. And by some strange miracle two of those things survive, they still exist, they still even work and I put in a picture of one of them. Next slide. That’s Glenn Seaborg on the occasion of receiving his PhD in 1937. That gets in ahead of this cut off date of 1940 for this thing. The next slide is me, that’s taken at a press conference held in Crocker laboratory on June 8th, 1940. The announcement of the discovery of neptunium, the first transuranium element. And they took a picture of me really making like a chemist there. Next slide. I found this slide in the archives and I couldn’t resist putting it in to end the slide show. I call it “On the beach”. Somewhere on the Sacramento delta, John Lawrence, Paul Aebersold and I are enjoying the sun with some girls. Now, if you were to look at that a while, maybe the sun will shine here. At this point I will end.

Sehr geehrte Damen und Herren, ich möchte mit einer kurzen Erklärung beginnen. Der Vortrag, den ich Ihnen heute halten werde, wurde ursprünglich zur Feier des 45jährigen Bestehens des Lawrence Labors in Berkeley geschrieben, die im letzten Jahr stattfand. Er sollte in einer als anekdotisch zu beschreibenden Form einen kurzen geschichtlichen Abriss geben, d. h. er behandelt sein Thema nicht auf strenge, sondern eher auf unterhaltsame Weise. Er beschäftigt sich ein wenig mit der wissenschaftlichen Geschichte des Labors, doch größtenteils handelt er von den Personen und davon, was in der Geschichte des Labors geschehen ist. Nach dieser kurzen Erläuterung beginne ich nun mit dem Vortrag, wie ich ihn gehalten habe. Es wird sich dabei um eine Multimedia-Präsentation handeln. Ich werde zunächst mit einer mehr oder weniger zusammenhängenden Darstellung beginnen und mit einer Diashow enden. Wenn ich von den Anfängen rede, so meine ich den Zeitraum bis zum Ende des Jahres 1940. Zu dieser Zeit machten sich viele Menschen in den USA über den Krieg in Europa große Sorgen. Einige hatten das Labor verlassen, um eine mit dem Krieg zusammenhängende Arbeit zu übernehmen, und schon bald übernahm auch das Labor selbst für den Krieg relevante Aufgaben. Ein großes Projekt für Friedenszeiten wurde im Jahre 1940 begonnen: das 184-Zoll-Zyklotron. Doch erst nach dem Krieg nahm das Projekt seine ursprüngliche Zielsetzung wieder auf. Der Berg über dem großen C - ich sollte erklären, dass es in Berkeley hinter der Stadt einen Berg gibt. Dort steht ein großes C (für „California“), das von den Studenten aufgestellt wurde. Der Ort über dem großen C wurde als Standort ausgewählt und Ende des Jahres 1940 war das Magnetfundament fertiggestellt und die untere Spule befand sich an Ort und Stelle. Dies war der Beginn der ersten Expansion des Labors über die Grenzen des Universitäts-geländes hinaus. Dieses Stadium des Labors und seine Vergrößerung gehören in einen Zeitraum, mit dem ich mich hier nicht beschäftigen werde. Die Errichtung des Strahlungslabors war die persönliche Leistung von Ernest Lawrence. Es war seine Idee. Er erhielt die finanzielle Unterstützung, organisierte die technische Ausrüstung, zog die Mitarbeiter an und lieferte natürlich die Grundidee: das Zyklotron. Viele andere Personen leisteten auf vielfältige Weise entscheidende Hilfe. Ich könnte den Universitätspräsidenten Sproul nennen und Leonard Fuller von der bundesstaatlichen Telefongesellschaft in der Universität, der die Spende eines großen Magneten für die 27 Zoll- und die 37-Zoll-Zyklotrone organisierte. Frederick Cottrell und Howard Poillon von der Forschungsgesellschaft. Und Francis Garvan von der Stiftung für Chemie, der auf Ernests Antrag auf Forschungsgelder wohlwollend reagierte. Raymond Birge, der 1932 Direktor des Instituts für Physik wurde. Donald Cooksey aus Yale, Stan Livingston, und viele andere. Doch es war das Labor von Lawrence. Diejenigen von uns, die in den Anfangstagen des Labors dort arbeiteten, erinnern sich noch daran, dass Ernest immer „DER BOSS“ war, und zwar in Großbuchstaben. Das war eine wichtige Unterscheidung. Er konnte mit Leuten sehr streng umgehen, wenn er den Eindruck hatte, dass sie nicht ihr Äußerstes gaben. Doch wog er dies durch die Großzügigkeit seines Lobes und dadurch auf, dass er für Ideen sorgte. Ich bin Rutherford nie begegnet, doch man hat mir gesagt, dass er denselben Charakter hatte, allerdings mit einem wichtigen Unterschied: Rutherford bevorzugte den einzelnen Forscher, der mit einfachen Apparaten arbeitete. Lawrence glaubte hingegen an Aufgaben, die so umfangreich waren, dass sie nur durch Teamarbeit zu bewältigen waren. Anfänglich stand hierauf eine Strafe. Die Bemühungen um größere Energie im Strahlstrom waren so fieberhaft, dass die Leute kaum Zeit zum Nachdenken hatten. So wurden wichtige Entdeckungen versäumt und einige Fehler gemacht. Doch diese Phase ging bald vorüber. Alles in allem glaube ich, dass Lawrence Recht hatte. Die schnelle Entwicklung des Zyklotrons war für die Nuklearforschung wichtiger als die Frage, wer welche Entdeckung gemacht hatte. Das Labor entstand 1931, und als ich gegen Ende des Jahres 1932 nach Berkeley kam, arbeitete es auf vollen Touren. Es gab dort nicht nur das 27-Zoll-Zyklotron, das Protonen von etwa 2 MeV lieferte, sondern auch die Sloan-Röntgenstrahlröhre, in die man, was ihren Nutzen für die Krebstherapie betraf, große Hoffnungen setzte. Außerdem hatte das Labor ein paar Linearbeschleuniger vom Widerøe-Typ, die von Dave Sloan, West Coates und Bernard Kinsey gebaut und eingesetzt wurden. Die Sloan-Röntgenstrahlröhre wurde in der klinischen Medizin viele Jahre lang verwendet, das Konzept des Linearbeschleunigers wurde jedoch aufgegeben. Während der Kriegsjahre wurde es später durch neue Ideen aus der Radarentwicklung wiederbelebt. Tatsächlich war das Labor Tag und Nacht ein sehr geschäftiger Ort, besonders wenn Ernest anwesend war, und das hieß: meistens. Ich begann mit meiner Forschung in Le Conte Hall, dem Physikgebäude der Universität von Kalifornien in Berkeley. Meine ersten Forschungen in Le Conte Hall beschäftigten sich mit dem Problem eines Molekülstrahls, doch ich gab sie auf, als das Ergebnis, das ich suchte, anderswo gefunden wurde. Ich trat daraufhin im Frühjahr des Jahres 1934 in die faszinierende Welt des Strahlungslabors ein. Stan Livingston, der Zyklotronfachmann und Telesio Lucci, ein pensionierter Kommandant der italienischen Marine, der ein vielgeliebter genereller Assistent und ein Faktotum war, gaben mir weisen Rat in der Frage, wie ich mich benehmen sollte. Da meine bisherige Erfahrung die eines Einzelforschers war, musste ich die Kunst der Teamarbeit erst lernen. Dies war offenbar keine einfache Sache, da niemand die verschiedenen Aufgaben, die zur Aufrechterhaltung des Zyklotronbetriebs erledigt werden mussten, routinemäßig koordinierte. Es gab zwei Gefahren: Man konnte entweder seine Pflichten vernachlässigen oder anderen im Wege stehen, indem man etwas zu tun versuchte, was jemand anderes tun sollte. Robert Oppenheimer war der leitende theoretische Berater des Labors, und er schlug vor, ich solle die Gammastrahlen untersuchen, die beim Beschuss leichter Elemente mit Protonen und Deuteronen erzeugt werden. Dies sollte sich als ein wichtiges Experiment heraustellen, denn ich entdeckte einen 5,5 MeV Gammastrahl, der beim Beschuss von Fluor mit Protonen entstand. Mit seiner Hilfe konnte ich die neue Theorie von Bethe und Heitler zur Absorbtion von Gammastrahlen durch Paarproduktion testen. Das Forschungsinteresse des Labors galt damals hauptsächlich den nuklearen Reaktionen, die man durch die Beobachtung der Protonen und Alpha-Teile studierte, die während eines Beschusses emittiert wurden. Sie wurden mithilfe einer schmalen Ionisationskammer nachgewiesen, die an einen für die Beobachtung von Gammastrahlen nicht geeigneten, linearen Verstärker angeschlossen war. Geigerzähler hielt man für unzuverlässig. Stan Livingston erzählt in einem Vortrag, den er 1967 in Texas gehalten hat, was am 24. Februar 1934 geschah, als das Labor von der Entdeckung der künstlichen Radioaktivität durch Joliot-Curie erfuhr. Sie verwendeten zum Zählen von Alpha-Teilchen einen Geigerpunktzähler (geiger point counter), ein Gerät, das uns heute ebenso exotisch vorkommt wie der Kohärer zur Zählung von Alpha-Teilchen. Es handelte sich dabei nicht um den geläufigen, zylindrischen Geiger-Müller-Zähler. Der Einfachheit halber wurden der Zyklotronoszillator und der Zählerschaltkreis zur Zeitsteuerung durch die beiden Pole eines doppelpoligen Messerschalters ein- und ausgeschaltet. Innerhalb einer halben Stunde wurde die Schaltanordnung so geändert, dass der Zähler eingeschaltet sein konnte, während das Zykloton ausgeschaltet war. Die Spannung des Zählers wurde so geändert, dass er Beta-Teilchen registrieren konnte. Das innere Zielrad wurde gedreht, um ein Kohlenstoff-Target in den Strahl zu bringen. Die Radioaktivität von Stickstoff-13 war zwar vorhanden, sie wurde allerdings durch eine andere Reaktion verursacht als diejenige, die seine Entdecker verwendeten. Anfänglich konnte diese Radioaktivität nicht beobachtet werden, was dem Labor einen Schlag versetzte, und so kam es zu einer natürlichen Reaktion gegen alle Geigerzähler. Das erste, was ich nach meinem Eintritt in das Labor unternahm, war eine Reise nach Pasadena, um von Charlie Lauritsen selbst zu lernen, wie man mit Quarzfasern ein Elektroskop baut. Ich hatte mein erstes Lauritsen-Elektroskop, das zur Erkennung von Gammastrahlen in einer Bleikugelkammer montiert war, erst seit wenigen Tagen, als Malcolm Henderson Mitte Mai zu mir kam und mir die Neuigkeit brachte, dass man in Rom durch Neutronen induzierte Radioaktivität entdeckt hatte. Er wollte mein Elektroskop verwenden, um sich einige dieser Abläufe anzuschauen. Es dauerte nur eine Weile, bis wir aus einer Blechdose mit einem dünnen Aluminium-fenster eine weitere Kammer angefertigt hatten, und die Blechdosenversion des Lauritsen-Elektroskops wurde zu einem wertvollen Instrument für die Beobachtung von Betastrahlen. Jack Livingood baute ein gleichartiges Elektroskop. Er verwendete es in einer äußerst umfangreichen Untersuchung, die er zusammen mit Seaborg und anderen durchführte. Sie untersuchten die Reaktionen, die bei vielen Elementen durch den Beschuss mit Deuteronen ausgelöst wurden. Dies führte in so kurzen Zeitabständen zur Entdeckung weiterer radioaktiver Isotope, dass dies mit der Häufigkeit neuer Entdeckungen in Rom vergleichbar war, nachdem Fermi die erste von Neutronen induzierte Radioaktivität beobachtet hatte. Einige der von ihnen entdeckten Isotope, wie zum Beispiel Jod-131, Eisen-59, Kobalt-60 und Technetium-99m, wurden in medizinischen und anderen Anwendungen sehr wichtig. Auf dem Gebiet der künstlichen Radioaktivität kam es zu einer großen Zunahme der Forschungsaktivität. Die Namen der Forscher sind zu zahlreich, um vollständig aufgeführt werden zu können. Stan Livingston und ich fanden eine radioaktive Form von Sauerstoff und Lawrence fand Kalium-24, was für eine Sensation sorgte, weil sich davon Proben mit hoher Radioaktivität herstellen ließen. Lawrence ließ dann sein Zyklotron-Team rund um die Uhr arbeiten, um für Demonstrationszwecke eine Probe mit einer Radioaktivität von 1 Curie herzustellen. Das war eine schwere Aufgabe. Jackson Laslett fand Kalium-22. Es hatte zunächst die längste Lebensdauer eines künstlich hergestellten radioaktiven Elements, wurde aber schon bald übertroffen. Martin Kamen und Sam Ruben fanden Kohlenstoff-14, das vielleicht wichtigste radioaktive Element von allen, usw. Außerdem wurden neue Arten von Aktivität entdeckt. Van Voorhis fand heraus, dass Kupfer-64 durch das Emittieren negativer oder positiver Elektronen zerfallen konnte. Dies war das erste bekannte Beispiel dieser Art von radioaktivem Zerfall. Und Luis Alvarez entdeckte die Art des Zerfalls, bei der ein Elektron aus einem inneren Orbital der Elektronenhülle eingefangen wird. Heute handelt es sich hierbei um einen bekannten Vorgang. Zu den neuen Vorgängen gehörten einige, die zu Atomzahlen führten, die von denen aller bekannten Elemente verschieden waren, sodass es sich um die Entstehung neuer Elemente handelte. Das erste von ihnen wurde 1937 von Emilio Segré und Carlo Perrier entdeckt. Sie arbeiteten in Palermo mit einem Stück Molybden, das sich an der Vorderkante einer Deflektorplatte im Zyklotron befunden hatte, wo es einem intensiven Beschuss ausgesetzt war. Segré hatte es nach einem Besuch im Sommer des Jahres 1936 mit nachhause genommen. Sie fanden darin das Element 43, das sie, nach dem griechischen Wort für „künstlich“, Technetium nannten, da es das erste künstlich hergestellte Element war. Element 85 wurde als nächstes künstlich hergestellt. Es wurde nach dem griechischen Wort für „instabil“ Astatin genannt wurde. Es wurde 1940 von Segré, Dale Corson und Ken MacKenzie gefunden. Wenig später im selben Jahr 1940 kam Phil Abelson, der ein Doktorand von Lawrence gewesen war, für einen kurzen Besuch zurück nach Berkeley und lieferte das fehlende Glied in der chemischen Bestimmung einer Aktivität, die in Uran durch den Beschuss mit Neutronen ausgelöst wurde und die ich schon seit einiger Zeit zu enträtseln versucht hatte. Ich habe sie in der Einleitung erwähnt. Dies war, wie ich erwartet hatte, das erste Element der Transurane. Ich nannte es nach dem Planeten Neptun Neptunium, ebenso wie Uran nach dem Planeten Uranus benannt worden war. Nachdem Phil Abelson wieder gegangen war, setzte ich die Arbeit fort und versuchte nun auch Uran mit Deuteronen zu beschießen. Dies führte zu einer Reihe anderer Isotope von Neptunium, als der Beschuss mit Neutronen, und ich fand Alpha-Teilchen-Aktivität, was auf das Vorhandensein des nächsten Elements der Transurane hindeutete. Denn nachdem man das Beta-Teilchen erhalten hatte, wäre der nächste Schritt normalerweise ein Alpha-Teilchen, und das ließ einen erwarten, dass dies das nächste sein würde. Ich nahm einige chemische Trennungen vor und konnte auf diese Weise zeigen, dass die Alpha-Aktivität nicht zu Uran oder Neptunium gehörte. Doch ich führte diese Untersuchung nicht zuende, weil mich Ernest Lawrence dazu überredete, für ein paar Wochen an das Massachusetts Institute of Technology (MIT) zu gehen, um dabei zu helfen, ein neues Labors für die Entwicklung von Mikrowellen-Radar einzurichten. Es wurde damals noch nicht Radar genannt. Dieses Wort wurde erst später eingeführt; doch wir begannen über Radar zu arbeiten. Als Deckname wurde das neue Labor das Strahlungslabor genannt. Es gab also zwei Strahlungslabors. Das sorgte manchmal für Verwirrung. Ich verließ Berkeley am 11. November 1940 und reiste mit dem Zug nach Boston. Am 28. November schrieb mir Glenn Seaborg, dass Art Wall einige sehr stark strahlende Neptunium-Proben hergestellt und gesagt hatte: In meiner Antwort am 8. Dezember sage ich: und es würde mich sehr freuen, wenn ihr an 93 und 94 weiterarbeiten könntet.“ Nun, nebenbei bemerkt, „so bald nicht“ sollte 5 Jahre bedeuten. Erst danach kehrte ich auf Dauer nach Berkeley zurück. Ernests Schätzung von ein paar Wochen habe ich nie geglaubt. Dies ist das Ende der Nebenbemerkung. Am 8. März 1941 schrieb mir Glenn und beschrieb den endgültigen chemischen Beweis dafür, dass die Alpha-Aktivität zum nächsten Element des Periodensystems gehörte, zu Plutonium. In diesem Briefwechsel verwendeten wir noch nicht die Namen der neuen Elemente, die noch nicht offiziell waren, sondern wir sprachen von 93 und 94, und der Brief vom März war mit dem Hinweis „vertraulich“ versehen. Wie Sie sehen, hielt Geheimhaltung bereits Einzug in die Kernforschung. Danach wurde die Geheimhaltung absolut, und für lange Zeit wurden keine dieser Dinge veröffentlicht. Er war der Erfinder der Methode, mit der sich das erzeugen ließ, was im Wesentlichen ein Strahl mit sehr langsamen Neutronen war. Dies gelang ihm durch das Pulsieren des Zyklotrons und dadurch, dass er den Detektor so einstellte, dass er nur zu einer bestimmten festgelegten Zeit nach der Emission des Neutronenpuls empfindlich war. Zusammen mit Ken Pitzer verwendete er diese Methode in einer Untersuchung der Neutronenstreuung durch die beiden Arten von molekularem Wasserstoff: von ortho- und para-Wasserstoff. Und mit Felix Bloch aus Stanford gelang ihm erstmals die Messung des magnetischen Moments des Neutrons. Eine der sich damals stellenden Fragen betraf die relative Stabilität der Kerne von – als Tritium bezeichnetem – Wasserstoff-3 und von Helium-3. Beide waren von Mark Oliphant am Cavendish Labor beobachtet worden. Sie waren die Produkte des Beschusses von Deuteronen mit Deuteronen. Alvarez und Bob Conrad zeigten als erste, dass Helium-3 stabiler ist, indem sie es Als sie daraufhin wussten, dass Wasserstoff-3 Beta-Teilchen emittieren muss, suchten sie nach Radioaktivität in mit Deuteronen beschossenem Deuteriumgas und fanden sie. So bestätigten sie, dass Tritium ein radioaktives Isotop ist. Gilbert Lewis am chemischen Institut der UC Berkeley spielte eine sehr wichtige Rolle in der Geschichte des Labors. Sobald die Entdeckung von Deuterium bekannt gegeben wurde, baute er Geräte auf, mit denen er durch Elekrolyse schweres Wasser erzeugen wollte, und er gab dem Labor eine Probe dieses schweren Wassers. Und im März 1933 wurde durch das Zyklotron der erste Strahl von Deuteronen erzeugt. Dies war ein sehr wichtiger Schritt. Von da an fand ein großer Teil der Arbeit mit Deuteronen statt. Sie sind viel ergiebiger und erzeugen Kernreaktionen, bei denen Protonen und Alpha-Teilchen entstehen. Ich sage „ergiebiger“, weil ich meine, dass erstens ihre Querschnitte größer sind, sodass man mehr Reaktionen erhält. Außerdem erhält man eine größere Vielfalt von Reaktionen, weil das Deuteron zwei Nukleonen enthält und man außerdem eine größere Vielfalt von Teilchen erhält. Lewis war, wie viele mit dem Labor assoziierte Personen, eine sehr schillernde Persönlichkeit. Er erzählte gern die Geschichte, wie er einer Fliege sein erstes schweres Wasser gefüttert hatte, und wie diese auf den Rücken gerollt sei und ihm zugezwinkert habe. Die zweite Anekdote habe ich selbst miterlebt. Eines Tages hörte Lewis während des Mittagessens im Faculty Club, wie sich einige Professoren darüber stritten, ob man Kindern beibringen sollte eine Zahlenspalte von oben nach unten oder von unten nach oben zu addieren. Lewis sagte daraufhin: Ich addiere sie zuerst von oben nach unten, dann von unten nach oben und dann nehme ich den Durchschnitt.“ Ich könnte Ihnen noch zahllose weitere Anekdoten erzählen. Das Labor wurde von zahlreichen Wissenschaftlern besucht, die dort für lange Zeit blieben und arbeiteten, u.a. von Jim Cork aus Michigan, Jerry Kruger aus Illinois, Lorenzo Emo, einem italienischen Graf, Harold Walke und Don Hurst vom Rutherford Labor, Wolfgang Gentner aus Germany, Maurice Nahmias aus Frankreich, Sten von Friesen aus Schweden, Ryokichi Sagane aus Japan und von Basanti Nag aus Indien. Die arbeitenden Besucher waren für das Labor sehr wichtig. Sie trugen nicht nur zum Forschungsprogramm bei, sondern sie nahmen die Fähigkeit, mit einem Zyklotron zu arbeiten, zu ihren eigenen Instituten mit zurück. Lawrence förderte diese Diffusion von Wissen aktiv, und Don Cooksey schrieb, was wir als „Kochbücher“ für die Arbeit mit dem Zyklotron bezeichneten. Sie wurden an nichtsahnende Institute verschickt, und viele Mitarbeiter des Berkeley Labors besuchten andere Einrichtungen, um an anderen Orten beim Design und der Herstellung von Zyklotronen behilflich zu sein. Milton White ging nach Princeton, Henry Newson nach Chicago, Hugh Paxton an das Joliot-Labor in Paris, Jackson Laslett nach Kopenhagen und Reg Richardson und Bob Thornton nach Michigan. Die Fähigkeit Zyklotrone zu bauen und das dazu erforderliche Know-how wurden schnell unter die Leute gebracht. Und ich glaube, dass diese Weitergabe von technischem Wissen, wie man es nennen mag, für den Fortschritt der Kernwissenschaft zum damaligen Zeitpunkt sehr wichtig war. Wir reden hier von den 1930er Jahren. Am Betrieb und der Wartung des Zyklotrons beteiligten sich zahlreiche Physiker. Für diese Aufgabe wurden eigens zuständige Teams eingeteilt. Ich erinnere mich, eine Zeit lang dem Eulen-Team zugeteilt worden zu sein, was mich nicht weiter störte, weil ich damals ein nachtarbeitender Junggeselle war. Für einige der anderen war es, wenn ich mich recht erinnere, allerdings ziemlich schwer. Wenn irgendein Problem vorlag, mussten wir das Zyklotron auseinandernehmen und versuchen es zu reparieren. Die größten Schwierigkeiten machten undichte Stellen, die das Vakuum beeinträchtigten, und das Abbrennen der Filamente in der Eisenquelle, die sich im Inneren des Zyklotrontanks sowie in den benötigten Oszillatorröhren befanden, die von Dave Sloan gebaut worden waren. Wenn das Eisenquellfilament erlosch, musste der Vakuumtank des Zyklotrons aus der Magnetlücke gerollt werden, dann die gewachste Verbindung zwischen der Abdeckung und dem Tank geöffnet und die Abdeckung entfernt werden. Anschließend musste das Filament ersetzt und alles wieder zusammengefügt werden: Die Verbindungen mussten wieder versiegelt, die Luft hausgepumpt werden, usw. Die Physiker bedienten jedoch nicht nur das Gerät. Art Snell und Ken MacKenzie bauten zum Beispiel Oszillatoren, Bob Wilson führte die erste theoretische Untersuchung der Stabilität von Umlaufbahnen durch und ich entwarf das Steuerungssystem für das 60-Zoll-Zyklotron. Ein Zeit lang übernahm ich zusätzlich noch die Aufgaben eines Elektroingenieurs. Dies war im Jahre 1938, und ein neues Betongebäude, das Crockery Labor, befand sich im Bau, um das neue, größere Zyklotron beherbergen zu können. Das Labor begann nun größer zu werden. Das führte zu einer wahren Revolution: keine undichten Wachsverbindungen mehr, keine Geräte, die mitten in einem wichtigen Experiment auseinanderfielen. Zumindest geschah dies nicht mehr so oft wie früher. Die „Faden-und-Wachs“-Schule der Physik hat für Oldtimer wie mich noch immer eine nostalgische Anziehungskraft, doch für größere Projekte, bei denen zahlreiche Leute von der Zuverlässigkeit von Geräten abhängen, eignet sie sich nicht. Win Salsbury und Bill Baker, beides Elektronik-Genies, übernahmen das Design und die Herstellung von Oszillatoren und anderen elektronischen Geräten. Eine Zeit lang kam Charlie Litton zu uns und zeigte uns zahlreiche Methoden der technischen Nutzung von Radiofrequenzen. Er besaß ein kleines Unternehmen in Redwood City, das er später an einige Unternehmer aus Texas verkaufte, die es zum Kern eines riesigen Konglomerats namens Litton Industries machten. Charlie verbrachte seinen Ruhestand in Grass Valley, wo er den Rest seines Lebens damit verbrachte, glücklich an einer Reihe unterschiedlicher Erfindungen zu arbeiten. Das Interesse an biomedizinischen Anwendungen entstand schon sehr früh. Ernests Bruder war Arzt und Ernest fühlte sich schon immer von der medizinischen Wissenschaft angezogen. Von der Sloan-Röntgenstrahlröhre, die ab 1934 in der Medizin zum Einsatz kam, habe ich bereits gesprochen. Im Jahr danach kam John für den Sommer nach Berkeley und stellte die ersten Beobachtungen zu den Auswirkungen der Neutronenstrahlen auf lebende Organismen an. Er stellte fest, dass diese Wirkungen stärker als bei anderen Formen der Strahlung und daher äußerst interessant waren. Paul Aebersold wurde der leitende Physiker der biomedizinischen Gruppe. Er traf die Vorkehrungen für Bestrahlungen und maß die Dosierung. Der erste Krebspatient wurde im September 1938 behandelt. Die Ergebnisse waren ermutigend genug, sodass das Crocker Labor sich der medizinischen Forschung widmete, obwohl es auch von Physikern und Chemikern genutzt werden durfte. Auch im biomedizinischen Bereich gab es „Arbeitsbesucher“. Frank Exner aus New York, Isidor Lampe aus Utah, Raymond Zirkle aus Pennsylvania, Al Marshak, Lowell Erf, John Larkin und viel andere. Dr. Joseph Hamilton leitete eine separate Gruppe, die untersuchte, auf welche Weise sich die Tieren und Menschen verabreichten radioaktiven Isotope im Körper verteilten. Zu den Gerüchen von heißem Öl, die das Zyklotron verursachte, kamen die von Tierkolonien hinzu. Wie Laslett es in seinem „Zyklotron-Alphabet“ sagte: Dann durchlebten wir die Zeit der WPA. Es war die Zeit während der Großen Depression, und die WPA war eine Regierungsprogramm, durch das Arbeitslose von der Regierung angestellt und Regierungsbehörden und anderen Institutionen zugewiesen wurden, um nützliche Arbeiten durchzuführen. WPA stand für „Works Progress Administration“ (Arbeitsfortschittsverwaltung). Ich bin im Besitz eines Briefes von Lawrence an die dieses Progamm organisierende Universitätsverwaltung aus dem Jahre 1934, in dem er für den Zeitraum von 1 Monat „(1) einen promovierten Physiker mit mehrjähriger Forschungserfahrung, Einige der Leute, die an diesem Programm teilnahmen, waren prägnante Gestalten. Besonders erinnere ich mich an Murray Rosenthal, der ein Hobby-Zauberer war, an einen schwedischen Zeichner namens Hallgren, der eine so lockere Ausdrucksweise hatte, dass wir versuchten, ihn von Don Cooksey fernzuhalten, der gegen seine Kraftausdrücke protestierte, und an einen Mann, der bei der Telefongesellschaft gearbeitet hatte, der ein sehr distinguiertes Aussehen hatte. Er liebte es, im Labor herumzugehen und mit einem Knopfhaken kräftig an Lötverbindungen zu ziehen, um zu überprüfen, wie fest sie waren. Einige, die nur vorübergehend eine schwierige Zeit durchmachten, blieben bei uns und wurden geschätzte Mitarbeiter des Labors. Eine ungefähre Vorstellung von den Geldern, um die es damals ging, erhält man durch die 1931 von Wally Reynolds vorgenommene Schätzung der Kosten für die Installation des 80 Tonnen schweren Magneten. Hierzu gehörten die Kosten seines Transports von San Francisco nach Berkeley und seine Installation an Ort und Stelle, die Kosten für 4 Transformatoren, einen Motorgeneratorsatz von 50 Kilowatt, einen 10 Tonnen schweren Kran, Betonpfeiler, Arbeitskräfteentwicklung sowie ein Budget für unvorhergesehene Kosten. Dies entsprach Gesamtkosten von 5300 Dollar. Es ist sehr schwer, eine Vorstellung von der Atmosphäre der damaligen Zeit zu vermitteln. Die Welt befand sich in einer tiefen Depression. Einige Leute an der Universität bezogen während des Streiks Position für die eine oder andere Seite. Freundschaften sind daran zerbrochen. Es gab eine intensive linksgerichtete Agitation, die für viele Wissenschaftler später schlimme Konsequenzen hatte. Kaum jemand hatte damals Geld. Sieben Monate lang, zwischen dem Ende meines Fellowships und meiner Anstellung als Fakultätsdozent, war ich Forschungsmitarbeiter ohne Gehalt. Doch irgendwie schlugen wir uns durch, und das Labor bestand fort. Lawrence war die treibende Kraft, und durch die Faszination seiner Entdeckungen blieb dem Labor der Elan erhalten. Es gab nur wenig Organisation: Lawrence war der Boss und das schien zu genügen. Wie groß waren die Veränderungen, die seither stattgefunden haben. Aus dem begeisterten Jugendlichen ist ein Erwachsener geworden, der über mehr Einfluss verfügt, es dafür aber auch mit den Problemen zu tun hat, die sich mit den reiferen Jahren einstellen. Damit habe ich das Ende der mehr oder weniger zusammenhängenden Geschichte erreicht, und jetzt kommt mein Dia-Vortrag. Ich habe etwa die Hälfte der mir zugestandenen Zeit benötigt, und ich werde nun also mit den Dias fortfahren. Könnte ich bitte das erste Dia haben? Dies ist Ernest Lawrence. Das Bild wurde am 19. September 1930 aufgenommen, direkt nachdem er in Berkeley auf einem Treffen der nationalen Akademie der Wissenschaften seinen ersten wissenschaftlichen Vortrag über das Zyklotron gehalten hatte. Er hält eine Apparatur aus Glass, Kupfer und Wachs in Händen, mit deren Hilfe er und Neils Edlefsen Beweismaterial für die Ionenresonanz in einem Magnetfeld erhalten hatten, wodurch Ernest ermutigt wurde, die Entwicklung der Zyklotronidee fortzusetzen. Seinem Gesichtsausdruck können Sie entnehmen, dass er voll Hoffnung für die Zukunft war. Sehen Sie, dies war im September 1930, bevor das Strahlenlabor ins Leben gerufen worden war, doch der kleine Apparat, den Lawrence in Händen hält, war dasjenige, was die ersten Hinweise darauf gab, dass das Zyklotron funktionieren könnte und was dafür sorgte, dass das Projekt fortgesetzt wurde. Jetzt das zweite Dia bitte. Es zeigt Stan Livingston und Ernest Lawrence neben dem großen Magneten in der Halle des „Pelton Water Wheel“-Unternehmens in San Francisco. Dieser Magnet war von der Federal Telegraph Company (der bundesstaatlichen Telefongesellschaft) in Palo Alto zur Verwendung als Teil des Poulsen-Senders (der ein Lichtbogensystem verwendet) hergestellt worden, den die chinesische Regierung bestellt hatte. Er wurde jedoch nie geliefert, und Leonard Fuller, der damals nicht nur Vizepräsident der Federal Telegraph Company in Palo Alto war, sondern auch Vorsitzender des Instituts für Elektroingenieurwesen in Berkeley, sorgte dafür, dass der Magnet stattdessen der Universität und den Forschern von Lawrence gegeben wurde. Und, wie ich bereits gesagt habe, zeigt dieses Bild, wie es in einen Zyklotronmagneten verwandelt wird. Der untere Pol wurde entfernt und es wurden zwei neue Pole hergestellt. Der Kern und die Pole des Magneten mussten verändert werden, um ihn als Magnet eines Zyklotrons verwenden zu können, und dies geschieht hier Ende des Jahres 1931. Ernest Lawrence baute das erste funktionsfähige Zyklotron. Nach dem kleinen Modell, das wir im letzten Bild gesehen hatten, übernahm Livingston die weitere Entwicklung und er baute das nächste Modell: ein Modell, das hervorragend funktionierte. Er fand einen Ionenstrahl aus Wasserstoffmolekülen mit einer Energie von 80.000 Elektronenvolt. Von Wasserstoffmolekülionen haben wir bereits etwas gehört: Sie sind das einfachste Molekül und daher das erste, was in einem Zyklotron beschleunigt wurde. Er fand sie am 2. Januar 1931 in einem 4-Zoll-Zyklotron. Dann baute er ein 11-Zoll-Zyklotron, mit dem Milt White 1932 die von Cockcroft und Walton gefundenen Zerfallsergebnisse für Lithium bestätigten konnte. Diese Arbeiten wurden in Le Conte Hall durchgeführt. Der große Magnet konnte jedoch nur in einem größeren Gebäude untergebracht werden. Wie Ihnen allen bekannt ist, war er einer der Entdecker oder Erfinder der starken Bündelung (strong focusing), ohne die der größte Teil der Hochenergiephysik nicht hätte erforscht werden können. Also: Lawrence erfand das Zyklotron, Livingston stellt eine funktionsfähige Version davon her, die erste, und die beiden sind wirklich die Erfinder dieser ganzen Sache. Drittes Dia. Dies zeigt das alte Strahlungslabor. Es diente vorher als Testlabor für das Bauingenieurwesen. Es hatte eigentlich abgerissen werden sollen, doch Ernest konnte Präsident Sproul, Präsident Sproul der Universität, nicht der USA, überreden, es zu erhalten. Wenn in einer amerikanischen Universitätsstadt vom „Präsidenten“ gesprochen wird, dann ist stets der Präsident der Universität gemeint, nicht der Präsident der Vereinigten Staaten. Ernest überredete also Präsident Sproul dazu, ihm das Labor für seine Experimente zu überlassen. Dies geschah am 26. August im Arbeitszimmer von Präsident Sproul. Ernest hatte damals die Zusage finanzieller Unterstützung und das offizielle Angebot für den Magneten. Wenn man einen Geburtstag für das Labor festlegen möchte, könnte es dieser Tag sein. Zu Beginn des Jahres 1932 wurde der Name „Strahlungslabor“ auf die Türen gemalt. Man kann dies in diesem Bild nicht erkennen. Damals, im Jahre 1932, stand auf allen Außentüren „Strahlungslabor“. Im Januar 1932 wurden der Magnet und ein 27-Zoll-Zyklotron aufgebaut. Im Juni dieses Jahres wurde es erstmals in Betrieb genommen. Sechs Jahre später wurden die Magnetpole vergrößert und das 37-Zoll-Zyklotron installiert. Und in einer Aufzeichnung vom 10. November 1937 fand ich das folgende Blatt von Martin Kamen. Natürlich war Martin Kamen ein Mann, der zusammen mit Sam Ruben Kohlenstoff-14 entdeckte. Außerdem schrieb er gern Gedichte folgender Art: Das Zyklotron, dies Biest, ist keinesweg entartet, Es funktioniert am besten, wenn man’s am wenigsten erwartet, Eins der schönsten dem Mensch beschied’nen Lose, Ist eine gute, dichte Dose. Mit „Dose“ meinte er natürlich das Vakuumgehäuse, so nannten wir es. Und Sie erinnern sich, was ich über das Elend der undichten Gehäuse gesagt habe. Denn das war es wirklich: ein Elend. Man verbrachte die ganze Nacht damit zu versuchen, eine undichte Stelle zu finden, und war es einem endlich gelungen, sie zu beheben, dann wurde das Wachs in die Kammer gesaugt und man musste wieder von vorne anfangen. In diesem Gebäude, das Sie hier sehen, befand sich ein großer Raum für das Zyklotron und seine Steuerungseinheiten. Es gab einen offenen Hof für Transformatoren und Schaltgeräte. Es gab einen Maschinenraum und einiges an Bürofläche. Wann immer es Probleme mit dem Gleichrichter oder dem Generator gab, der den Strom für den Magneten erzeugte, rief man mich, um das Problem zu lösen. Man hielt mich damals für einen Experten, wenn es darum ging, mit einem Kolben zu schweißen. Ich erinnere mich daran, dass Franz Kurie, als er den Motor des Generators einschaltete, einmal die Schalter in der falschen Reihenfolge umlegte und dadurch alle Lampen in ganz Berkeley durchbrennen ließ. Dieses Gebäude wurde Zeuge von Frustration und Begeisterung, von menschlichen und wissenschaftlichen Dramen. Über das, was dort geschah, hat man sich viele Anekdoten erzählt, z. B. die Geschichte, dass Ernest Lawrence Bill Baker und bei einer anderen Gelegenheit Bob Wilson gefeuert hat und seine Kündigungen später widerrief und sie erneut aufnahm. Alles in allem waren die Beziehungen der Forscher untereinander, in Anbetracht der vielen verschiedenen Temperamente der Leute, erstaunlich harmonisch. Nach dem Krieg wurden in diesem Gebäude die ersten Tests des Synchrozyklotron-Prinzips durchgeführt, und Melvin Calvin unternahm hier seine bahnbrechenden Arbeiten zum Kohlenstoffzyklus und zur Photosynthese. Nun schauen wir uns das 4. Dia an. Dies ist eine andere Ansicht desselben Gebäudes: Sie stammt aus dem Jahr 1959. Das Gebäude wird gerade abgerissen. Der Abriss erfolgt in Richtung des Betrachters des letzten Dias, in der Richtung, die im letzten Bild auf den Betrachter gezeigt hätte. Von dem Gebäude ist nicht mehr viel stehen geblieben. Dort stehe ich und betrachte traurig das Ende einer Ära. Später musste auch das Crocker Labor abgerissen werden. Das chemische Institut benötigte mehr Platz für weitere Gebäude. Das war also tatsächlich das Ende einer Ära, denn in diesem alten Gebäude fanden die Anfänge der gesamten Kernforschung statt, die mit Zyklotronen, Beschleunigern, kreisförmigen Beschleunigern durchgeführt wurde. Dies ist das 27-Zoll-Zyklotron von 1932. Die Vakuumkammer sehen Sie in der Mitte. Sie befindet sich zwischen den beiden Polen. Sie selbst und der Magnet sind völlig mit Wachs überzogen. Damals wurde alles mit Wachs überzogen. In dem nach oben verlaufenden Laderohr auf der Vorderseite, in der Mitte dieses Rohres befindet sich ein gespannter Draht, der die Verbindung zum gebündelten Strahlenstrom herstellt bzw. ihn zu einem Galvanometer auf dem Steuerungstisch weiterträgt, der sich hier links außerhalb des Bildes befand. Und auf der Vorderseite der Vakuumkammer befindet sich, zum Betrachter herausstehend, der von Malcolm Henderson gebaute Linearverstärker, der zum Zählen von Protonen und Alpha-Teilchen verwendet wurde. Die Windungen des Magneten wurden durch Öl in diesen großen runden Behältern gekühlt. Sie waren randvoll mit Öl, das von einer Pumpe in einem Kreislauf bewegt wurde. Alles war ständig vollkommen mit Öl überzogen. Einmal vergaß Luis Alvarez ein Ventil zu schließen, nachdem er die Ölzirkulationspumpe ausgeschaltet hatte. Daraufhin lief der gesamte Tank aus und das Öl gelangte durch Risse im Boden in das Untergeschoss. Ich erinnere mich noch daran, dass dies ein sehr dramatischer, von einem Nobelpreisträger ausgelöster Zwischenfall war. Dies zeigt Ernest auf der anderen Seite des Zyklotrons, ebenfalls im Jahr 1932. Dieses Foto hat sein eigenes Datum, das auf dem Wasserstoffbehälter im Vordergrund steht. Hier können Sie es nicht lesen, auf dem Original ist es jedoch sichtbar. Hinter Ernest sehen Sie den Oszillator, der das Zyklotron mit Hochfrequenzstrom versorgte. Sie sehen auf diesem Bild, dass er eine kommerzielle Vakuumröhre verwendet, doch diese waren sehr teuer. Daher verwendeten wir eine Zeit lang selbstgebaute Röhren, die Dave Sloan entworfen hatte. Sie konnten demontiert werden. Sie hatten eine Wachsverbindung, sodass man sie auseinandernehmen und die Filamente auswechseln konnte. Ernest war als einer der besten Experimentalphysiker der Welt ankannt, doch über eine besondere manuelle Geschicklichkeit verfügte er nicht, weshalb er zu den Beschädigungen der Apparate seinen Beitrag leistete, wie wir alle. Wenn irgendeine besonders kniffelige Aufgabe anstand, wandte er sich an jemand anderen und sagte: Wichtig waren seine Ideen und seine Begeisterung. Nun das nächste, das 7. Dia. Dies ist Dave Sloan mit seinem „Röntgenstrahlgrab“ (x-ray tomb), wobei es sich im Wesentlichen um eine Testschleife und ein Vakuumgehäuse handelte. Dieses Röntgenstrahlgrab war das erste Gerät, das in diesem Gebäude aufgestellt wurde. Wie ich Ihnen ja bereits erzählt habe, wurde der große Magnet erst 1932 aufgestellt, dieses Gerät jedoch bereits 1931. Dave war für das Labor sehr wichtig. Er konnte alles bauen und war voller genialer Einfälle. Er baute große Öldiffusionspumpen, als man solche Geräte noch nicht kaufen konnte, und er fertigte die montierbaren Oszillatorröhren an, in denen man die Filamente wechseln konnte, indem man eine Wachsverbindung löste. Einmal versuchte er eine Diffusionspumpe mit Hilfe von Wismutdampf herzustellen. Dies funktionierte zwar nicht besonders, doch es war eine interessante Idee. Bei Physics International war er weiterhin aktiv und arbeitete mit Starkstrombeschleunigern, was eine natürliche Fortsetzung seiner vorherigen Arbeit war. Nächstes Dia. Hier ist ein weiteres Dia des Labors, die Werkstatt des alten Strahlungslabors. Ohne solche Werkstätten hätte das Labor seine Arbeit nicht durchführen können. Wir verwendeten unsere eigene Werkstatt und auch die Werkstatt in Le Conte Hall, die Werkstatt des physikalischen Instituts. Größere Aufträge wurden an kommerzielle Werkstätten vergeben. In dieser Darstellung sehen Sie links George Krause und rechts Eric Lehman, die an einem Zyklotrongehäuse arbeiten, oder die zumindest so aussehen, als überlegten sie, ob sie daran arbeiten sollten. Im Vordergrund sitzen Don Cooksey, der als allgemeine Unterstützungskraft im Labor sehr hilfreich und als Organisator sehr wichtig war (er machte die Werkstätten zu einer seiner Hauptaufgaben), und Jack Livingood, der große Jäger nach radioaktiven Isotopen. Dieser Mann hier in der Ecke ist Livingood. Drei Männer, die seit ihren Anfängen in der Werkstatt gearbeitet haben, Don Stallings, Jack Kroll und Paul Wells, arbeiten noch immer für das Labor. Das nächste Dia ist Dia 9. Es zeigt Art Snell, Franz Kurie und Bernard Kinsey, die sich – wenn ich mich recht erinnere – im Strawberry Canyon Schwimmbad befanden, als dieses Foto aufgenommen wurde. Ich war fast versucht zu sagen, dass sie sich im Schwimmbad von Bad Schachen befinden, doch der Hintergrund stimmt dafür nicht, und auch die Zeit stimmt nicht. Art Snell kam 1934 aus Montreal und ging später nach Chicago. Heute ist er in Oak Ridge. Er war berühmt als der Dichter des Labors. Er dichtete zu allen Gelegenheiten Limericks. Als Lawrence 1939 den Nobelpreis erhielt, schickte er ein Telegramm, auf dem stand: Er baute außerdem einen Oszillator und entdeckte, unter anderem, radioaktives Argon. Franz Kurie, der Mann in der Mitte, scheint einen Tarzanschrei auszustoßen, doch er war tatsächlich ein sehr sanftmütiger Mensch. Er führte die Nebelkammertechnik in das Labor ein. Er nahm Messungen der Energieverteilung von Betastrahlen vor und erfand eine Methode zur Darstellung der Daten von Betastrahlverteilungen, die es leicht machte, die obere Grenze der Energie zu bestimmen. Diese Methode wird heute als Fermi-Kurie-Diagramm bezeichnet. Sie wurde vielfach verwendet. Bei einer Untersuchung der Zertümmerung von Stickstoff durch Neutronenbeschuss fand er einige ungewöhnliche Spuren, die sich so deuten ließen, als wären sie darauf zurückzuführen, dass langsame Elektronen eingefangen und Protone emittiert wurden, wodurch es zur Entstehung von Kohlenstoff-14 kam. Diese Beobachtung von Kurie diente als Schlüssel bei der Suche nach der besten Methode zur Gewinnung von Kohlenstoff-14, die – wie Sie aus dem Gesagten erraten können – darin besteht, dass kleine Neutronen von Stickstoff eingefangen werden. Für eine ziemlich lange Zeit hatte ich eine Flasche Ammoniumnitrat, die sich in der Nähe des Zyklotron-Targets befand. Ich hatte gehofft, eines Tages Kohlenstoff daraus zu trennen und zu prüfen, ob er radioaktiv war. Diese Flasche wurde umgestoßen, und ich habe sie nie ersetzt. Sie stand den Leuten im Weg, und einige hatten sogar Angst, sie könnte explodieren. Es war zu einigen Explosionen gekommen, bei denen Ammoniumnitrat im Spiel war. Doch ich glaube nicht, dass eine kleine Laborflasche sehr gefährlich war. Als Kohlenstoff-14 schließlich identifiziert und Kohlenstoff mit Deuteronen beschossen wurde, versuchten Kamen und Ruben Stickstoff dann mit Neutronen zu beschießen. Sie kehrten anschließend nie wieder zum Beschuss von Kohlenstoff zurück, da hierbei die Erträge geringer waren und der radioaktive Kohlenstoff mit all dem gewöhnlichen Kohlenstoff „verdünnt“ war. Franz Kurie war später der Leiter des Radio- und Tonlabors der US-Marine in San Diego. Und der dritte Mann, Bernard Kinsey, war ein Commonwealth Fellow aus England. Er baute einen Linearbeschleuniger für Lithiumionen. Es gibt viele Geschichten über Bernard. Er konnte sich sehr stark aufregen und hatte eine sehr komplizierte und abwechselungsreiche Art zu fluchen. Er hatte das Fluchen wirklich zu einer Kunst entwickelt. Er war hier auf dieser Feier, und vielleicht lässt er sich überreden, uns eine Kostprobe von seiner Kunst zu geben. Es gab noch einen anderen Commonwealth Fellow an der Universität, Brown war sein Name. Das war wahrscheinlich der faulste Mann, dem ich je begegnet bin. Ich glaube nicht, dass er jemals irgendetwas getan hat. Wann immer ich ihn im Faculty Club traf, wo ich damals wohnte, war er offensichtlich nicht im Labor. Ernest hätte ihn rausgeworfen. Nun kommen wir zu Dia 10. Dies ist das Crockery Labor, das ich früher bereits erwähnt habe. Das alte Strahlungslabor befindet sich links auf der rechten Seite, wenn man einen schmalen Weg überquert, und das 60-Zoll-Zyklotron befindet sich in dem hohen Teil am hinteren Ende dieses Gebäudes. Es wurde als das medizinische Zyklotron bezeichnet, doch wurde es – wie ich schon sagte – von anderen mitbenutzt. Es wurde 1939 in Betrieb genommen. Es lieferte Deuteronen von etwa 9 Millionen Elektronenvolt. Unter der Aufsicht von Dr. Joseph Hamilton wurde es ausgiebig zur Erzeugung von radioaktiven Isotopen eingesetzt, die zu medizinischen Zwecken und als Tracer verwendet wurden. Nun zum nächsten Dia. Hier sehen Sie das 60-Zoll-Zyklotron, Don Cooksey und Ken Green. Sie sehen, dass es wesentlich ordentlicher aussieht, als die früheren Zyklotrone. Bill Brobeck war unser erster Ingenieur. Dies war auf seinen Einfluss zurückzuführen. Die Struktur, die auf der rechten Seite hervorsteht, bestand aus einem Behälterpaar, in denen sich die D-Stämme befanden, die ein Resonanzsystem ausmachten. Die Oszillatoren befanden sich auf dem Balkon auf der rechten Seite. Am oberen Rand erkennen Sie eine Spule aus einem dicken Kabel, diese Spule hier oben. Es übertrug hohe Spannungen an die Deflektorplatte des von Ed Lofgren gebauten Gleichrichters. Der Grund für die Spule ist, dass Hochspannungskabel normalerweise an den Enden defekt werden und dass sie sehr schwer zu spleißen sind. Die Spule enthielt also sehr viel Kabelvorrat für Reparaturen. Nächstes Dia. Dies ist ein Blick durch das Fenster in den Kontrollraum des 60-Zoll-Zyklotrons. Links sehen Sie Bill Brobeck, unseren Ingenieur und Bob Wilson, der seine Pfeife raucht. Bob Wilson ist heute natürlich der Direktor des Fermi-Labors in Batavia in Illinois. Und dann sehen Sie dort Ernest Lawrence und eine Reihe anderer Leute. Einer von ihnen bin ich. Wer der Mann hinter mir ist, habe ich vergessen. Diese temporäre Einrichtung, die die Ordnung des Steuerungstisches stört, war ein Prototyp eines automatischen Magnetstromregulators, der gerade getestet wurde. Nächstes Dia. Dies zeigt eine Gruppe von Leuten. Wer der Mann auf der linken Seite ist, habe ich vergessen. Der nächste ist Ernest Lawrence, der ein Manuskript in Händen hält. Dale Corson, ein Physiker, der jetzt Präsident der Cornel Universität ist. Winfield Salisbury unser Elektronikgenie und Luis Alvarez, der einer der Preisträger ist. Corson war an der Entdeckung von Astatin beteiligt und ist jetzt Präsident der Cornel Universität. Salisbury verfolgte seit seinem Ausscheiden aus dem Labor eine ausgezeichnete Karriere in der Industrie und in der akademischen Welt. Er lieferte sehr wertvolle Beiträge zu Radarabwehrmaßnahmen während des Krieges. Luis erhielt, wie sie wissen, später den Nobelpreis für Physik usw. Nächstes Dia. Dies zeigt John Lawrence, den Bruder von Ernest Lawrence, der hier 1936 mit einer Reihe von Mäusekäfigen im Hintergrund aufgenommen wurde, was ein für einen biomedizinischen Forscher angemessener Kontext ist. Zu den biomedizinischen Forschungen werde ich nichts Weiteres sagen, da das Programm, dem sie galten, noch von einem anderen Redner abgedeckt werden wird. Hier sehen Sie wieder Mäusekäfige, diesmal mit Mäusen darin, doch zu einem späteren Datum, 1939. Die Person ist eine andere: Dr. Joseph Hamilton. Dr. Hamilton verfügte über einen Arbeitsbereich im Crockery Labor, wo er mit radioaktiven Isotopen medizinische und biologische Untersuchungen durchführte. Seine Arbeit erschloss wissenschaftlliches Neuland. Er ermittelte die Stoffwechselpfade der Schwermetalle in Tieren und im Menschen. Joes Mittagstafel im Faculty Club war für seine interessanten Gespräche zu vielen Themen bekannt. Ich erinnere mich, dass er einen besonderen Tisch hatte, eine Art „Stammtisch“. Ich saß regelmäßig an diesem Tisch und wir diskutierten über alles. Nächstes Dia. Es war nicht alles harte Arbeit. Wir hatten auch Spaß. In einem kleinen Dorf in der Nähe von Berkeley gab es ein italienisches Restaurant namens Di Biasi’s. Die Di-Biasi-Parties waren berühmte, jährliche Feiern des Labors. Bei diesen Gelegenheiten entspannten wir uns und hatte Spaß. Dies ist Paul Aebersold. Er ist der Physiker, der mit dem Biologen und den Medizinern zusammenarbeitete, und die Geräte einrichtete, Dosierungen maß, die Patienten vorbereitete usw. Der Mann mit dem Kuchen hier, Paul Aebersold, hatte einen nicht zu unterdrückenden Sinn für Humor. Er war stets der Zeremonienmeister. Diese Party im Jahre 1939 fand zur Feier des 60-Zoll-Zyklotrons statt. Paul überreichte einen zyklotronförmigen Kuchen, auf dem die Worte standen: Das sollte eine völlige Übertreibung sein, doch das Bevatron war noch nicht erfunden. Sie erinnern sich daran, dass wir schon wenige Jahre später 6 Milliarden Volt hatten. Das entsprach fast dieser Zahl, die als maßlose Übertreibung gedacht war. Lawrence befindet sich rechts im Vordergrund, und der Mann im mittleren Vordergrund, Sten von Friesen, ist ein Besucher aus Schweden. Nächstes Dia. Auf derselben Party war auch Martin Kamen, der Mann auf der linken Seite, der über irgendetwas rätselt. Neben ihm steht Sten von Friesen, Bob Cornog, der zusammen mit Alvarez arbeitete und an der Entdeckung von Wasserstoff-3 beteiligt war. Links im Hintergrund ist da noch Ken MacKenzie. Es ist ein wenig dunkel hierfür. Auf der rechten Seite, dort im Hintergrund sieht man Mrs Lawrence, Ernests Ehefrau, zwischen zwei hohen Besuchern: Vannevar Bush auf unserer linken und Alfred Loomis auf unserer rechten Seite. Alfred war ein sehr guter Freund von Ernest und dem Labor, und er half auf vielfältige Weise. Nächstes Dia. Das ist Lorenzo Emo Capodilista, der italienische Graf, den ich eingangs erwähnte. Er war eine der schillernden Figuren in der Anfangszeit des Labors. Er kam 1935 an das Labor und blieb mehrere Jahre. Seinen Nachnamen, Capodilista, verwendete er nicht. Er bedeutet „ganz oben auf der Liste“. Es war scheinbar ein sehr alter italienischer Name. Er war ein ausgesprochen liebenswerter Zeitgenosse. Dies ist Charlie Litton. Der Mann, der zu uns kam und uns bei vielen technischen Problemen half und dessen Name in Verbindung mit Litton Industries verwendet wurde. Er arbeitete mit einer Glasplatte, die er selbst hergestellt hatte. Die Hauptsache, sein originelles Produkt waren derartige Glasplatten. Nächstes Dia. Dies ist Maurice Nahmias aus Joliot-Curies Labor in Frankreich, der hier im Jahr 1937 mit der Vakuumkammer für das 37-Zoll-Zyklotron posiert. Nächstes Dia. Das ist Henry Newson, der 1934 aus Chicago kam, mit einem Doktor in Chemie. Ich meine, er passt sehr gut in diese Gruppe hier. Er kam als Doktor der Chemie, aber er verließ uns als Physiker. Er führte einige höchst einfallsreiche Experimente durch, wozu er den Rückstoß künstlich erzeugter radioaktiver Kerne verwendete. Das Bild wurde im Jahre 1938 aufgenommen. Das nächste Dia. Dies sind Ernest und Molly Lawrence mit ihren ersten beiden Kindern, Eric und Margaret. Sie hatten schließlich sechs Kinder, doch dies war der Anfang. Dieses Bild wurde auf den Stufen des Crocker Labors aufgenommen. Nächstes Dia. Diese Aufnahme zeigt Ernest Lawrence im Jahr 1939 beim Schreiben des Skripts für einen Film über den Nobelpreis. Er verwendet einfach den Kotflügel eines PKWs als Schreibfläche für sein Skript. Gehen wir weiter zum nächsten Dia. Das ist Lee de Forest, der Erfinder, der Mann, der das Raster in das Vakuumgrab brachte, der das Labor besuchte. Wir hatten viele angesehene Besucher im Labor, und ich habe zwei Bilder in die Diaserie aufgenommen. Dies ist de Forest. Nun kann ich Ihnen das nächste Dia zeigen. Es zeigt Diego Rivera mit Lawrence. Diego Rivera war natürlich der mexikanische Wandmaler, und er kam nach San Francisco und erstellte ein Wandgemälde an der Wand eines der dortigen Gebäude. Ich erinnere mich daran, dass ich dorthin fuhr und ihm bei der Arbeit zusah. Wir kommen zum Ende. Nächstes Dia. Es sollte eigentlich um 90° gedreht sein, aber es geht auch so. Das ist eines der original 1934 Lauritsen-Elektroskope, die ich gebaut habe, als ich mich dem Labor 1934 anschloss und das ich für meine frühen Arbeiten verwendete. Und dank eines seltsamen Wunders überleben zwei solcher Dinger. Es gibt sie noch, sie funktionieren sogar noch, und ich habe ein Foto von ihnen in die Diaserie aufgenommen. Nächstes Dia. Das ist Glenn Seaborg anlässlich der Verleihung seines Doktorgrads im Jahre 1937. Das liegt noch vor der zeitlichen Grenze von 1940 für diesen Vortrag. Auf dem nächsten Dia bin ich selbst zu sehen. Es wurde am 8. Juni 1940 bei einer Pressekonferenz im Crocker-Labor aufgenommen. Der Anlass war die Verkündung der Entdeckung von Neptunium, des ersten der Transurane. Und sie nahmen ein Bild von mir auf, auf dem ich mich wie ein echter Chemiker gebe. Nächstes Dia. Ich fand dieses Dia in den Archiven und ich konnte der Versuchung nicht widerstehen, es zum Schluss zu zeigen. Ich nenne es „Am Strand“. Irgendwo im Sacramento Delta genießen John Lawrence, Paul Aebersold und ich mit einigen Mädchen die Sonne. Wenn Sie sich das eine Weile anschauen, beginnt die Sonne vielleicht auch hier zu scheinen. Hiermit möchte ich schließen.

Edwin McMillan on the use of radioactive tracers
(00:23:24 - 00:24:38)

 

X-rays : clinical diagnosis and radiotherapy

Röntgen’s “X-ray photograph” of his wife’s hand was the first example of projectional radiography, and was understandably welcomed by the medical community. It could now be possible to see broken bones, and locate foreign bodies such as bullets and shrapnel. Radiation therapy using X-rays was also put into practice remarkably soon after their discovery. The first medical uses were for health conditions such as eczema and lupus, and the first cancer treatment using X-rays was reported in France in 1896. The drawback of these early treatments was the large damage done to normal tissue due to the low energies of the X-rays. Patients as well as doctors suffered from burns and deformities, and deaths as a result of radiation sickness frequently occurred in the first decades of X-ray use. Fortunately, the initial problems of low penetration of X-rays were largely overcome by the middle of the 20th century. Projectional radiographs became a mainstay of medical imaging. In radiation therapy, the development of compact linear accelerators that were able to rotate around patients boosted survival rates for cancer patients. As with radioisotope therapy, it took decades to figure out the appropriate dosage rates for various malignancies and how to maximise the efficacy of treatment. During the 10th Lindau Nobel Laureate Meeting, physician and Nobel Laureate William Parry Murphy explained the modern-day method of treating leukemia using X-rays:

 

William Murphy (1960) - X-Ray Treatment of Chronic Leukemia

Distinguished guests, ladies and gentlemen. I must first apologise for not giving my address in German. I’m sure, however, that you will understand my Boston and perhaps Cambridge English much better than my German. (Applause) I sort of feel that you might feel just now very much as I did quite a number of years ago after listening to these 2 beautifully presented papers this morning with so much important information. Quite a number of years ago when I was taking my examinations to practice medicine in the state of Massachusetts, part of the examination was an oral one. Each physician spent several minutes discussing their own subject with a candidate: surgery, internal medicine, paediatrics and so on. So after having been in conference with the surgeon for some minutes and not feeling too happy about the outcome, I approached the next man who asked me what I intended to do. I said, “I thought I’d practice medicine.” He said, “Are you interested in obstetrics?” He smiled and said: “Well that happens to be my subject to examine you on.” And he said, “I rather judge you won’t be very much interested in my questions, so let’s just relax and talk a few minutes.” So I feel perhaps that what we should do now is just relax, rather than trying to struggle through a discussion of the treatment of leukaemia. The work that I want to present today was originally planned as a joint report with the late Doctor Merrill Sauceman, who was a Harvard Medical School professor of radiology at Peter Bent Brigham Hospital. The work deals with certain data concerning 107 patients with chronic leukaemia treated at the hospital by Roentgen irradiation for the most part in cooperation with Dr. Sauceman until his retirement in 1956. An attempt has been made to include in this group only those with chronic leukaemia, although it’s a well recognised fact that it’s not always possible to distinguish between the chronic and the acute or subacute varieties. May I have the first slide please. The diagnosis was ordinarily made on the basis of the clinical evaluation and the peripheral blood picture. This just shows a low-power photomicrograph of the picture in chronic lymphocytic leukaemia. If there were blast forms present in any considerable degree or number, the condition was considered to be acute rather than chronic. The next slide please. I’m sorry that these do not show up well. The next slide. This is a high-power of the lymphocytic and a low-power of granulocytic. And the next one shows a higher power of the granulocytic. The next slide please. You see an eosinophil in the far corner and a myelocyte in the centre. It is not my intention today to try to discuss the nature of the leukaemic process or the aetiology of the disease. Such a discussion would entail considerable speculation and perhaps theory and it would not help us to solve the problem of treatment, at least for the present. We do, however, now consider leukaemia as a malignant cancer and we know that there are certain irritants that do tend to precipitate the disease. That is irradiation; chemical, physical and viral irritations have been shown to produce the disease in some instances. During the earlier years, as was the prevailing custom, and occasionally later, treatment was directed either to the spleen, the chest, the long bones or masses of lymph nodes. Following the remission treatment was usually withheld until another relapse occurred and the general condition of the patient was poor. The rather large doses of x-rays required were frequently followed by anorexia, severe nausea and vomiting and general malaise. After recovery from this there was a short period with some degree of wellbeing, followed by the next relapse and then of course requiring another round of treatment. It was observed, however, that treatment over the long bones only was followed by a satisfactory response of the leukocytes but with less of the toxic effects so frequently observed following treatment of the spleen or chest. In view of these facts it was decided that the method of treatment would be modified in 2 major respects in the belief that some of the unpleasant effects of therapy could be avoided and also that we might perhaps actually increase the lifespan. The first modification was to apply treatment in small dosage over the entire trunk from the mid-thighs upward at 1 metre distance alternating front and back, so-called Teleoroentgen therapy. The second modification was to start treatment when the leukocyte levels tended to rise above 40,000 cells per mm^3 rather than waiting until a more severe relapse, thus maintaining a rather uniformly near normal leukocyte level. This we decided to refer to as spray technique as opposed to the local application previously used. Doses of from 15 to 50 or 60 Roentgens were used depending upon the patient’s condition and the effect anticipated. This method used was discussed in a paper in 1940. The spray technique was introduced in the early part of 1934 and with few exceptions has been used as the principle method of treatment since that time in our clinic. Local treatment to masses of lymph nodes or to the spleen was used when it was indicated. In order to compare the relative effects of the spray and local techniques, the patients treated by each method are considered separately according to the predominating technique used. A few of each group also received some form of chemical therapy at some time during the course of their illness. May I have the next slide please? The patients with granulocytic leukaemia were divided equally in respect to sex. In the lymphocytic group there were 27 male and 20 female. Now this slide shows the age at onset or the first definite signs or symptoms recognised as manifestations of the disease. The age differed somewhat in the 2 groups. In the lymphocytic group we find only 6 of the patients developing the disease before the 5th decade, whereas in the granulocytic group, to your right, over half of the patients developed the disease before the 5th decade. In other words the granulocytic leukaemia is a disease of younger people ordinarily, although again you see at the bottom in the 8th decade 1 patient in the lymphocytic group and 2 in the granulocytic. The youngest patient in the lymphocytic was 36 and in the granulocytic 23. And the oldest in each of the groups was 82 and 85 at the time of onset. May I have the next slide please? The results of treatment as indicated by length of survival after onset by the 2 techniques used are shown in these next 2 slides. The percentage of patients surviving 3 years... these represent the years of survival, 3 to 7. The survival percentage in the 2 groups was about the same in the groups treated by spray or by local in both series: However, at 4 years there’s some difference: Following through with the lymphocytic at 5 years 59% under spray treatment survive and only 27 under local treatment. The survival percentage was the same in both forms of treatment in the granulocytic group. And at 7 years 47% of the patients were still alive by the spray method and only 20 with the local treatment. The next slide please. This shows the classification according to years, the number of patients still living at those intervals. The average survival rate in the lymphocytic leukaemia patients treated by the spray method was 6.8 years and in those treated by the local method 4.6. In the granulocytic group the comparable figures are 3.1 and 2.8. Moffitt and Lawrence have cited 31 instances of leukaemia surviving at least 5 years. McGavran cited 1 instance of a patient surviving 25 years. Taking that into consideration we have here 5 patients surviving 10 years; 1 11, 12, 16, 17 and 26 years. That seems to be about the longest survival. In the granulocytic group 2 patients survived 9 years. The figures indicating survival time, as shown in these 2 slides, compare favourably with those recorded in previously reported series. They also suggest some advantage in duration of survival time for those treated by the spray method as opposed to the local technique although this advantage is not striking. There has, however, been a great difference between the effects of the 2 techniques in respect to the condition of the patients during their illness. Those treated in large dosage locally over the chest or spleen and at the time of severe relapse have, as I’ve previously noted, experienced periods of rather disturbing malaise, anorexia, nausea and vomiting after their treatment with only brief periods of wellbeing between time. Whereas those treated with the small dosage by spray technique have suffered few ill effects as the result of treatment and have in general lived normal lives carrying on their usual occupations throughout their periods of illness. The mild anorexia or nausea which occurred in the occasional patient was readily controlled by intramuscular injections of 50 to 100 mg of pyridoxine hydrochloride. Those who experienced nausea or anorexia on the first exposure were after that treated 1 hour or 2 with pyridoxine before the next x-ray treatment was given. It may be profitable to record briefly the regimen recommended for the management of treatment in the patient after the diagnosis has been established. This will of course vary depending on many circumstances. If the leukocyte level is high, the patient with all pertinent data regarding history and blood picture is referred to the radiologist for treatment. Spray treatment may be applied daily, or on alternate days, and must be controlled by leukocyte counts before each exposure. Pyridoxine should be injected before each treatment if indicated. Treatment is continued in small dosage until the leukocyte level has dropped to 30,000 or perhaps lower, depending upon the rate of the drop. As one may expect the count to continue to drop for several days after treatment is stopped, it is desirable to check the count in about a week as a guide to subsequent courses of treatment. The patient should be seen and the count checked thereafter every 4 to 6 weeks. When there is again a tendency for the leukocytes to increase, In this way an attempt is made to maintain fairly uniform and near normal leukocyte levels. This method of treatment, always carried out in consultation between the physician and radiologist, is used for control of the leukocytes, though massive enlargement of lymph nodes may require local therapy for their control. It’s rarely necessary to treat the spleen locally even though it’s slightly enlarged, for if one uses spray treatment regularly, the size of the spleen usually subsides also. If the leukocyte level is not high when the diagnosis is made, treatment should be delayed until such time as the patient either shows definite indications of a relapse approaching, or, preferably, as the leukocyte count rises to above 40,000. May I have the next slide? This patient was followed for 5 years before treatment was started. This shows the 5-year period. Although his leukocyte count was tending to rise, treatment was not started for he was asymptomatic. He did have arthritis. Note that this was before the days of cortisone but that was not very troublesome. The next slide shows the course of events during treatment which he was still living at the end of 5 years. And in all lived 7 years during the course of treatment during which time, as you will see, the leukocyte levels were maintained low and his general physical health was excellent. He worked regularly and subsequently died, at a time when the leukaemia was well controlled, of a coronary heart attack. This patient lived in all 12 years during the time that his disease was recognised. May I have the next slide? If the lymph node enlargement is the presenting problem such as in this patient, local application rather than spray will be indicated. This is illustrated by this patient whose complaint was of deafness. His aurist thought this might be due to pressure from enlarged lymph nodes, which proved to be the case for when the lymph nodes were treated his deafness totally disappeared. May I have the next slide? And subsequently he was followed with spray treatment but, unfortunately, circumstances were such that he died 2 years later. Death was not related to the leukaemia, however, but he had a haemorrhage, a gastric haemorrhage, one very stormy, snowy night on his farm in Canada which was 20 miles from the nearest medical attention. His history suggested that the haemorrhage was from a peptic ulcer. He had been up to that time in excellent condition so far as the leukaemia was concerned. And although he was then 72 years of age I suspect that he would have had a rather long survival period. The results of treatment in the granulocytic group have not been quite so satisfactory in general as those in the lymphocytic. And yet the majority have been remarkably well and able to carry on their usual activities throughout their illness. An example of this, of the granulocytic well-controlled therapy, is this next slide which shows the course of the blood picture in a man who is a model maker in a brass foundry at which he continued to work throughout this 3.5-year period without periods of illness. The arrows at the bottom indicate when the treatments were given in order to keep the leukocyte count low. As a terminal event he developed severe pain in the head and abdomen, sugar became present in the urine in large amounts. He became comatose and, for the first time during his illness, was hospitalised where he died a few days later from a condition which was diagnosed at post mortem examination as cerebral thrombosis. I feel sure that this had nothing to do with the leukaemic process. Unfortunately, a few of our patients were not available for or did not, for one reason or another, follow up treatment in the prescribed manner and so our figures do not show up so well as they might if we could have controlled them better. The causes of death, as observed in this series, are interesting, particularly in that they indicate that more than half of the patients died from diseases not directly related to leukaemia. May I have the next slide? Of the 105 patients who have died, the cause of death in 69 has been established as other than leukaemia. Post mortem examination confirmed the cause of death in 35 of this group. Perhaps those who died from pneumonia or haemorrhage for example should be included with those who died from a disease directly related to leukaemia. The cause of death for 35 patients is recorded as due to leukaemia. Those with severe haemolytic anaemia, localised infection, progression of the leukaemia due to refusal of therapy and a few in whom no other cause could be determined I included in this group. Pneumonia was considered to be the cause of death in 11 patients as you see at the top. This was the most frequent cause of death. However, if one considers all of the cardiovascular group together, there were 21 which is by far the larger number. It is also of interest to note that of the 10 patients who died of multiple infarcts The other 4 patients died of complications directly resulting from chemotherapy. Death followed the use of TEM, nitrogen mustard, aminopterin and urethane together with intravenous injections of ACTH in 1 patient each. The causes of death are otherwise recorded in the table and so are not here considered as caused by chemotherapy: Again 4 different chemicals were responsible: nitrogen mustard, TEM, mercaptopurine with cortisone and Myleran each in 1 patient. The chemotherapy was not, however, carried out by us. You may take that slide off if you wish, although I would like you to note particularly that 5 of our patients died from tuberculosis, and I’ll mention those a little later on, and several from haemorrhage, perhaps because of their severe anaemia, and 6 from sepsis. A solution of potassium arsenide, Fowler’s solution, was used in a number of instances, particularly during the earlier years, but was discontinued because of its unpleasant side effects. At no time during this period of treatment had he been free from severe anorexia and nausea and malaise so that he had lost 40 pounds during that period of time. He was started on spray treatment and within a few weeks had regained his weight for he had no further nausea or vomiting, and lived 2 more years under spray therapy, 4 years in all. The published results of chemotherapy have not been sufficiently impressive to induce us to abandon spray x-ray therapy in its favour. Because we’ve had little personal experience with the use of chemicals other than Fowler’s solution, it is not our intention to attempt to evaluate the comparative effect of x-rays and chemotherapy. A brief record of the experience of some of our patients who received chemotherapy may be of interest and instructive. These patients received it at some time during their period of illness but not as the main course of treatment. Urethane was discontinued after short periods of trial by 6 patients because of anorexia and nausea and vomiting. It was tolerated but had little clinical effect in 1 patient. TEM was discontinued in 1 patient because of anorexia and nausea and in another after twice causing severe leucopoenia. This second patient died of pulmonary tuberculosis after the last trial of TEM. Aminopterin was used once but stopped because of unfavourable effects. Cortisone was given to 4 patients, 2 of whom also received antibiotics. and the forth of a cerebral vascular accident 3 weeks after starting cortisone. These unfavourable experiences with chemotherapy are not sufficient to condemn this method, particularly in view of the fact that it has been given in a few instances in which the disease may have been in a terminal stage regardless of the type of therapy used. However, in comparison with the absence of toxic effects following the use of x-rays in small dosage by the spray technique and because of the lack of evidence of superiority of chemotherapy over that of spray x-ray and reports thus far available, one may question the advisability of further experiment with the chemicals presently in use. Lawrence has reported on favourable experiences with the use of radioactive phosphorus, P32. And Osgood has compared the effects of P32 with the spray therapy showing no definite advantage of one over the other. Where spray treatment is available, it would seem to be the treatment of choice for the patient with chronic leukaemia. Unfortunately, the research during the past 40 years has not produced a strikingly important development for the treatment of chronic leukaemia. Perhaps the most important development has been the introduction of the spray method of Roentgen irradiation, as used in this series of patients, which has tended to minimise some of the unpleasant side effects of therapy and so allowed the patients to live more comfortably and normally throughout their illness. There may also have been added a few years to the lifespan, and even more may be possible, now that infections may be controlled and the use of the sulphonamides and antibiotics available. The majority of the patients in this series were treated before these substances were generally available. Anaemia has been a frequent and important complication as might be expected. Transfusions have been given when indicated. They have, undoubtedly, added both to the lifespan and to the comfort of the patient. Both iron and injections of either liver extract or vitamin B12 have been used in some patients for control of the anaemia but probably not with strikingly beneficial effects, for we have seen the blood levels improve after spray therapy or x-ray therapy whether or not these substances were given. Experimental work in the future in order to be successful in the management of leukaemia, whether acute or chronic, must be directed toward finding a means of encouraging normal production or maturation of leukocytes rather than their destruction. All of our methods of therapy up to date are designed to destroy cells rather than to increase their production or maturation from a normal point of view. Or one must direct attention toward prevention of the disease by recognition of those factors which may initiate the abnormal growth of cells so that these may be avoided. I have already commented on those irritants that are known. And by controlling exposure to these I am sure that some cases of leukaemia can be prevented. I hope that we can learn more of the mechanism by which these substances do produce irritation and so produce leukaemia and in the near future be able to prevent rather than try to cure the disease which now of course is incurable. Thank you.

William Murphy explaining the modern-day method of treating leukemia using X-rays
(00:07:33 - 00:09:02)

 

In the next lecture fragment, Murphy disapproves of the use of chemotherapy to treat chronic leukemia, but the rapid development of chemotherapy drugs in the second half of the 20th century has replaced X-rays as the standard routine for treating this disease, despite the fact that the side effects mentioned by Murphy still remain a significant problem for many cancer patients.

 

William Murphy (1960) - X-Ray Treatment of Chronic Leukemia

Distinguished guests, ladies and gentlemen. I must first apologise for not giving my address in German. I’m sure, however, that you will understand my Boston and perhaps Cambridge English much better than my German. (Applause) I sort of feel that you might feel just now very much as I did quite a number of years ago after listening to these 2 beautifully presented papers this morning with so much important information. Quite a number of years ago when I was taking my examinations to practice medicine in the state of Massachusetts, part of the examination was an oral one. Each physician spent several minutes discussing their own subject with a candidate: surgery, internal medicine, paediatrics and so on. So after having been in conference with the surgeon for some minutes and not feeling too happy about the outcome, I approached the next man who asked me what I intended to do. I said, “I thought I’d practice medicine.” He said, “Are you interested in obstetrics?” He smiled and said: “Well that happens to be my subject to examine you on.” And he said, “I rather judge you won’t be very much interested in my questions, so let’s just relax and talk a few minutes.” So I feel perhaps that what we should do now is just relax, rather than trying to struggle through a discussion of the treatment of leukaemia. The work that I want to present today was originally planned as a joint report with the late Doctor Merrill Sauceman, who was a Harvard Medical School professor of radiology at Peter Bent Brigham Hospital. The work deals with certain data concerning 107 patients with chronic leukaemia treated at the hospital by Roentgen irradiation for the most part in cooperation with Dr. Sauceman until his retirement in 1956. An attempt has been made to include in this group only those with chronic leukaemia, although it’s a well recognised fact that it’s not always possible to distinguish between the chronic and the acute or subacute varieties. May I have the first slide please. The diagnosis was ordinarily made on the basis of the clinical evaluation and the peripheral blood picture. This just shows a low-power photomicrograph of the picture in chronic lymphocytic leukaemia. If there were blast forms present in any considerable degree or number, the condition was considered to be acute rather than chronic. The next slide please. I’m sorry that these do not show up well. The next slide. This is a high-power of the lymphocytic and a low-power of granulocytic. And the next one shows a higher power of the granulocytic. The next slide please. You see an eosinophil in the far corner and a myelocyte in the centre. It is not my intention today to try to discuss the nature of the leukaemic process or the aetiology of the disease. Such a discussion would entail considerable speculation and perhaps theory and it would not help us to solve the problem of treatment, at least for the present. We do, however, now consider leukaemia as a malignant cancer and we know that there are certain irritants that do tend to precipitate the disease. That is irradiation; chemical, physical and viral irritations have been shown to produce the disease in some instances. During the earlier years, as was the prevailing custom, and occasionally later, treatment was directed either to the spleen, the chest, the long bones or masses of lymph nodes. Following the remission treatment was usually withheld until another relapse occurred and the general condition of the patient was poor. The rather large doses of x-rays required were frequently followed by anorexia, severe nausea and vomiting and general malaise. After recovery from this there was a short period with some degree of wellbeing, followed by the next relapse and then of course requiring another round of treatment. It was observed, however, that treatment over the long bones only was followed by a satisfactory response of the leukocytes but with less of the toxic effects so frequently observed following treatment of the spleen or chest. In view of these facts it was decided that the method of treatment would be modified in 2 major respects in the belief that some of the unpleasant effects of therapy could be avoided and also that we might perhaps actually increase the lifespan. The first modification was to apply treatment in small dosage over the entire trunk from the mid-thighs upward at 1 metre distance alternating front and back, so-called Teleoroentgen therapy. The second modification was to start treatment when the leukocyte levels tended to rise above 40,000 cells per mm^3 rather than waiting until a more severe relapse, thus maintaining a rather uniformly near normal leukocyte level. This we decided to refer to as spray technique as opposed to the local application previously used. Doses of from 15 to 50 or 60 Roentgens were used depending upon the patient’s condition and the effect anticipated. This method used was discussed in a paper in 1940. The spray technique was introduced in the early part of 1934 and with few exceptions has been used as the principle method of treatment since that time in our clinic. Local treatment to masses of lymph nodes or to the spleen was used when it was indicated. In order to compare the relative effects of the spray and local techniques, the patients treated by each method are considered separately according to the predominating technique used. A few of each group also received some form of chemical therapy at some time during the course of their illness. May I have the next slide please? The patients with granulocytic leukaemia were divided equally in respect to sex. In the lymphocytic group there were 27 male and 20 female. Now this slide shows the age at onset or the first definite signs or symptoms recognised as manifestations of the disease. The age differed somewhat in the 2 groups. In the lymphocytic group we find only 6 of the patients developing the disease before the 5th decade, whereas in the granulocytic group, to your right, over half of the patients developed the disease before the 5th decade. In other words the granulocytic leukaemia is a disease of younger people ordinarily, although again you see at the bottom in the 8th decade 1 patient in the lymphocytic group and 2 in the granulocytic. The youngest patient in the lymphocytic was 36 and in the granulocytic 23. And the oldest in each of the groups was 82 and 85 at the time of onset. May I have the next slide please? The results of treatment as indicated by length of survival after onset by the 2 techniques used are shown in these next 2 slides. The percentage of patients surviving 3 years... these represent the years of survival, 3 to 7. The survival percentage in the 2 groups was about the same in the groups treated by spray or by local in both series: However, at 4 years there’s some difference: Following through with the lymphocytic at 5 years 59% under spray treatment survive and only 27 under local treatment. The survival percentage was the same in both forms of treatment in the granulocytic group. And at 7 years 47% of the patients were still alive by the spray method and only 20 with the local treatment. The next slide please. This shows the classification according to years, the number of patients still living at those intervals. The average survival rate in the lymphocytic leukaemia patients treated by the spray method was 6.8 years and in those treated by the local method 4.6. In the granulocytic group the comparable figures are 3.1 and 2.8. Moffitt and Lawrence have cited 31 instances of leukaemia surviving at least 5 years. McGavran cited 1 instance of a patient surviving 25 years. Taking that into consideration we have here 5 patients surviving 10 years; 1 11, 12, 16, 17 and 26 years. That seems to be about the longest survival. In the granulocytic group 2 patients survived 9 years. The figures indicating survival time, as shown in these 2 slides, compare favourably with those recorded in previously reported series. They also suggest some advantage in duration of survival time for those treated by the spray method as opposed to the local technique although this advantage is not striking. There has, however, been a great difference between the effects of the 2 techniques in respect to the condition of the patients during their illness. Those treated in large dosage locally over the chest or spleen and at the time of severe relapse have, as I’ve previously noted, experienced periods of rather disturbing malaise, anorexia, nausea and vomiting after their treatment with only brief periods of wellbeing between time. Whereas those treated with the small dosage by spray technique have suffered few ill effects as the result of treatment and have in general lived normal lives carrying on their usual occupations throughout their periods of illness. The mild anorexia or nausea which occurred in the occasional patient was readily controlled by intramuscular injections of 50 to 100 mg of pyridoxine hydrochloride. Those who experienced nausea or anorexia on the first exposure were after that treated 1 hour or 2 with pyridoxine before the next x-ray treatment was given. It may be profitable to record briefly the regimen recommended for the management of treatment in the patient after the diagnosis has been established. This will of course vary depending on many circumstances. If the leukocyte level is high, the patient with all pertinent data regarding history and blood picture is referred to the radiologist for treatment. Spray treatment may be applied daily, or on alternate days, and must be controlled by leukocyte counts before each exposure. Pyridoxine should be injected before each treatment if indicated. Treatment is continued in small dosage until the leukocyte level has dropped to 30,000 or perhaps lower, depending upon the rate of the drop. As one may expect the count to continue to drop for several days after treatment is stopped, it is desirable to check the count in about a week as a guide to subsequent courses of treatment. The patient should be seen and the count checked thereafter every 4 to 6 weeks. When there is again a tendency for the leukocytes to increase, In this way an attempt is made to maintain fairly uniform and near normal leukocyte levels. This method of treatment, always carried out in consultation between the physician and radiologist, is used for control of the leukocytes, though massive enlargement of lymph nodes may require local therapy for their control. It’s rarely necessary to treat the spleen locally even though it’s slightly enlarged, for if one uses spray treatment regularly, the size of the spleen usually subsides also. If the leukocyte level is not high when the diagnosis is made, treatment should be delayed until such time as the patient either shows definite indications of a relapse approaching, or, preferably, as the leukocyte count rises to above 40,000. May I have the next slide? This patient was followed for 5 years before treatment was started. This shows the 5-year period. Although his leukocyte count was tending to rise, treatment was not started for he was asymptomatic. He did have arthritis. Note that this was before the days of cortisone but that was not very troublesome. The next slide shows the course of events during treatment which he was still living at the end of 5 years. And in all lived 7 years during the course of treatment during which time, as you will see, the leukocyte levels were maintained low and his general physical health was excellent. He worked regularly and subsequently died, at a time when the leukaemia was well controlled, of a coronary heart attack. This patient lived in all 12 years during the time that his disease was recognised. May I have the next slide? If the lymph node enlargement is the presenting problem such as in this patient, local application rather than spray will be indicated. This is illustrated by this patient whose complaint was of deafness. His aurist thought this might be due to pressure from enlarged lymph nodes, which proved to be the case for when the lymph nodes were treated his deafness totally disappeared. May I have the next slide? And subsequently he was followed with spray treatment but, unfortunately, circumstances were such that he died 2 years later. Death was not related to the leukaemia, however, but he had a haemorrhage, a gastric haemorrhage, one very stormy, snowy night on his farm in Canada which was 20 miles from the nearest medical attention. His history suggested that the haemorrhage was from a peptic ulcer. He had been up to that time in excellent condition so far as the leukaemia was concerned. And although he was then 72 years of age I suspect that he would have had a rather long survival period. The results of treatment in the granulocytic group have not been quite so satisfactory in general as those in the lymphocytic. And yet the majority have been remarkably well and able to carry on their usual activities throughout their illness. An example of this, of the granulocytic well-controlled therapy, is this next slide which shows the course of the blood picture in a man who is a model maker in a brass foundry at which he continued to work throughout this 3.5-year period without periods of illness. The arrows at the bottom indicate when the treatments were given in order to keep the leukocyte count low. As a terminal event he developed severe pain in the head and abdomen, sugar became present in the urine in large amounts. He became comatose and, for the first time during his illness, was hospitalised where he died a few days later from a condition which was diagnosed at post mortem examination as cerebral thrombosis. I feel sure that this had nothing to do with the leukaemic process. Unfortunately, a few of our patients were not available for or did not, for one reason or another, follow up treatment in the prescribed manner and so our figures do not show up so well as they might if we could have controlled them better. The causes of death, as observed in this series, are interesting, particularly in that they indicate that more than half of the patients died from diseases not directly related to leukaemia. May I have the next slide? Of the 105 patients who have died, the cause of death in 69 has been established as other than leukaemia. Post mortem examination confirmed the cause of death in 35 of this group. Perhaps those who died from pneumonia or haemorrhage for example should be included with those who died from a disease directly related to leukaemia. The cause of death for 35 patients is recorded as due to leukaemia. Those with severe haemolytic anaemia, localised infection, progression of the leukaemia due to refusal of therapy and a few in whom no other cause could be determined I included in this group. Pneumonia was considered to be the cause of death in 11 patients as you see at the top. This was the most frequent cause of death. However, if one considers all of the cardiovascular group together, there were 21 which is by far the larger number. It is also of interest to note that of the 10 patients who died of multiple infarcts The other 4 patients died of complications directly resulting from chemotherapy. Death followed the use of TEM, nitrogen mustard, aminopterin and urethane together with intravenous injections of ACTH in 1 patient each. The causes of death are otherwise recorded in the table and so are not here considered as caused by chemotherapy: Again 4 different chemicals were responsible: nitrogen mustard, TEM, mercaptopurine with cortisone and Myleran each in 1 patient. The chemotherapy was not, however, carried out by us. You may take that slide off if you wish, although I would like you to note particularly that 5 of our patients died from tuberculosis, and I’ll mention those a little later on, and several from haemorrhage, perhaps because of their severe anaemia, and 6 from sepsis. A solution of potassium arsenide, Fowler’s solution, was used in a number of instances, particularly during the earlier years, but was discontinued because of its unpleasant side effects. At no time during this period of treatment had he been free from severe anorexia and nausea and malaise so that he had lost 40 pounds during that period of time. He was started on spray treatment and within a few weeks had regained his weight for he had no further nausea or vomiting, and lived 2 more years under spray therapy, 4 years in all. The published results of chemotherapy have not been sufficiently impressive to induce us to abandon spray x-ray therapy in its favour. Because we’ve had little personal experience with the use of chemicals other than Fowler’s solution, it is not our intention to attempt to evaluate the comparative effect of x-rays and chemotherapy. A brief record of the experience of some of our patients who received chemotherapy may be of interest and instructive. These patients received it at some time during their period of illness but not as the main course of treatment. Urethane was discontinued after short periods of trial by 6 patients because of anorexia and nausea and vomiting. It was tolerated but had little clinical effect in 1 patient. TEM was discontinued in 1 patient because of anorexia and nausea and in another after twice causing severe leucopoenia. This second patient died of pulmonary tuberculosis after the last trial of TEM. Aminopterin was used once but stopped because of unfavourable effects. Cortisone was given to 4 patients, 2 of whom also received antibiotics. and the forth of a cerebral vascular accident 3 weeks after starting cortisone. These unfavourable experiences with chemotherapy are not sufficient to condemn this method, particularly in view of the fact that it has been given in a few instances in which the disease may have been in a terminal stage regardless of the type of therapy used. However, in comparison with the absence of toxic effects following the use of x-rays in small dosage by the spray technique and because of the lack of evidence of superiority of chemotherapy over that of spray x-ray and reports thus far available, one may question the advisability of further experiment with the chemicals presently in use. Lawrence has reported on favourable experiences with the use of radioactive phosphorus, P32. And Osgood has compared the effects of P32 with the spray therapy showing no definite advantage of one over the other. Where spray treatment is available, it would seem to be the treatment of choice for the patient with chronic leukaemia. Unfortunately, the research during the past 40 years has not produced a strikingly important development for the treatment of chronic leukaemia. Perhaps the most important development has been the introduction of the spray method of Roentgen irradiation, as used in this series of patients, which has tended to minimise some of the unpleasant side effects of therapy and so allowed the patients to live more comfortably and normally throughout their illness. There may also have been added a few years to the lifespan, and even more may be possible, now that infections may be controlled and the use of the sulphonamides and antibiotics available. The majority of the patients in this series were treated before these substances were generally available. Anaemia has been a frequent and important complication as might be expected. Transfusions have been given when indicated. They have, undoubtedly, added both to the lifespan and to the comfort of the patient. Both iron and injections of either liver extract or vitamin B12 have been used in some patients for control of the anaemia but probably not with strikingly beneficial effects, for we have seen the blood levels improve after spray therapy or x-ray therapy whether or not these substances were given. Experimental work in the future in order to be successful in the management of leukaemia, whether acute or chronic, must be directed toward finding a means of encouraging normal production or maturation of leukocytes rather than their destruction. All of our methods of therapy up to date are designed to destroy cells rather than to increase their production or maturation from a normal point of view. Or one must direct attention toward prevention of the disease by recognition of those factors which may initiate the abnormal growth of cells so that these may be avoided. I have already commented on those irritants that are known. And by controlling exposure to these I am sure that some cases of leukaemia can be prevented. I hope that we can learn more of the mechanism by which these substances do produce irritation and so produce leukaemia and in the near future be able to prevent rather than try to cure the disease which now of course is incurable. Thank you.

William Murphy disapproving of the use of chemotherapy to treat chronic leukemia
(00:28:11 - 00:29:53)

 

X-rays are now used more often as a powerful diagnostic tool than as a means of killing tumours. Soon after Myrphy’s lecture in Lindau, Allan McLeod Cormack published two papers on the mathematics of emission scanning using X-rays, which could greatly improve radiotherapy. As the only nuclear physicist in Cape Town in the mid-1950s, Cormack was asked to work part-time in the radiology department of a local hospital, and was struck by the fact that the planned radiotherapies directed X-rays at patients as if they were homogeneous, such as “a block of wood or a tank of water”, to quote Cormack, without consideration of the various absorptions of human tissues. He set out to solve the problem, but his theoretical solutions aroused almost no interest. In 1971, Cormack learned of the EMI-scanner, the first computed tomography machine, developed by Godfrey Hounsfield:

Cormack presenting the EMI-scanner - the first computed tomography machine
(00:14:37 - 00:17:00)

 

Cormack and Hounsfield were jointly awarded the Nobel Prize in Physiology or Medicine in 1979 for their independent work on “the development of computer assisted tomography”, and over time, the EMI-scanner became today’s computed tomography (CT) scanner, which enables physicians and radiologists to visualise cross-sections of internal organs or particular tissues, also in three dimensions. CT has become a fundamental part of medical research and clinical diagnosis. But as noted in Cormack’s lecture, it can be used in many other disciplines, such as archaeology, geology, or materials science. Beyond CT and medical research, X-ray technology is now used to observe outer space through X-ray astronomy, to study molecular structure, or in material processing technologies, to name just a few applications.

The question of the safety of radioactivity

The multitude of discoveries concerning radiation and radioactivity made an enormous impact on physics, chemistry, biology and medicine. New scientific fields emerged and promising technologies were introduced, yet the use of nuclear weapons during World War II and the contamination resulting from nuclear testing prompted scientists to rethink attitudes towards peacetime uses of radiation as well. At the time, limiting unnecessary exposure to radiation by patients and doctors was not a priority. Since the 1920s, shoe shops in Britain and the U.S. were endowed with shoe-fitting fluoroscopes, which enabled customers to view x-ray images of their feet in order to choose the right shoe size. This invention was particularly directed at children. As the field of genetics began to take shape, many began to ask what was the impact of radiation dosage on human DNA. It was in this atmosphere that Hermann Joseph Muller (Nobel Prize in Physiology and Medicine, 1946) voiced his fears concerning genetic damage in the expected age of radiation, “I cannot find justification for the large doses received in medical irradiation.”

 

Hermann Muller (1955) - The Effect of Radiation and other Present Day Influences Upon the Human Genetic Constitution

To begin with, I would like to express my appreciation and my sincere gratitude to the administration of the town of Lindau and to the hosts of this meeting for presenting us scientists with the opportunity to take part in these five days of mutual intellectual fertilisation, to get to know each other at a personal level and to enjoy your endearing hospitality in this beautiful and interesting environment. Above all, it is an encouraging example particularly for Americans to see to what intellectual and cultural heights a town as small as Lindau can raise itself – and also what sacrifices it is willing to make for this development. And now, if you pardon me, I should like to return to my mother tongue, English. This is because I fear, or, in a certain sense, I indeed hope that my German is worse than my genetics. Each cell contains a great collection of thousands of different genes, arranged in line in the chromosomes. It is by the interactions of the chemical products of these genes that the composition and structure of every living thing is determined. Each gene reproduces itself exactly, forming a daughter gene just like itself before each cell division. Thus, the daughter cells and individuals of later generations have genes like those originally present. However, these genes are subject to rare ultramicroscopic chemical accidents called gene mutations that usually strike but one gene at a time. The mutant gene that resulting from a mutation thereafter produces daughter genes that have the mutant composition. Thus, descendants arise which have some abnormal characteristic. These characteristics are of many thousands of diverse kinds. Very rarely a mutant gene arises which happens to have an advantageous affect. This allows the descendents who inherited to multiply more than the other individuals in the population. Until finally individuals with that mutant gene become so numerous as to establish the new type as the normal type, replacing the old. This process continued step after step, constitutes evolution. However, since the mutations result from ultramicroscopic chemical accidents, a mutant gene is in more than 99% of cases detrimental. That is it produces some kind of harmful effect, some disturbance of function. The disturbance may be enough to kill with certainty any individual who has inherited a mutant gene of this kind, this same kind from both his parents. An individual whom we will call homozygous because he has inherited the same kind of gene from both. Such a mutant gene which kills with certainty is called a lethal. More often the effect is not fully lethal but only somewhat detrimental, giving rise to some risk of premature death or failure to reproduce but not a 100% certainty of it. Now in the great majority of cases an individual who receives a given mutant gene from one of his parents receives from the other parent a corresponding but unlike gene, one of the original normal type. He is said to be heterozygous in contrast to homozygous. In the heterozygous individual it is usually found that the normal gene is dominant, the mutant gene recessive. That is the normal gene usually has much more influence than the mutant gene in determining the characteristics of the individual. However, exact studies show that the mutant gene is seldom completely recessive. It does usually have some slight detrimental affect on the heterozygous individual, subjecting him to some risk of premature death or failure to reproduce. That is a risk of genetic extinction. This risk is commonly of the order of a few percent down to some small fraction of 1%. It is readily seen that if a mutant gene causes an average risk of extinction of, for instance 5%. That is a chance of 1 in 20 of dying off without leaving offspring like itself. This mutant gene will on the average pass down through about 20 generations before the line of decent containing this gene is extinguished. Because that risk will continue generation after generation until extinction does occur. And a 1/20th chance in each generation takes on the average 20 generations to reach its fruition. It is therefore said that the persistence, P of that particular gene is 20 generations. There is some reason to estimate that the average persistence of mutant genes in general may be something like 40. Although there are vast differences between mutant genes in this respect. That would mean the risk of the extinction in any one generation of 2½%. Observations on the frequency of certain mutant characteristics in man, supported by recent more exact observations on mice by Russell working at Oak Ridge indicate that any one given gene on the average, any one gene, undergoes one mutation of a given type per generation among 50,000 to 100,000 human germ cells. That is the mutation frequency for one gene which we call My. Haldane invented this terminology, the Greek letter My for mutation. My for one gene. Observations on the fruit fly drosophila show that there are all together at least 10,000 times as many different mutations occurring as those of a given type in a given gene altogether. Now since it is very likely that man is at least as complicated genetically as the fly drosophila, we must multiple our figure of one in 100,000 which to be conservative we assume for one type of mutation by at least 10,000 to get a minimum estimate for the total number of mutations arising in each generation in all genes together in human germ cells. That is one in 10 to one in 5 according to whether we take one in 100,000 or one in 50,000. Now every individual, each of us, arises from 2 germ cells, sperm and egg and therefore contains twice this number of newly arisen mutations. That is 2 in 10 to 4 in 10. This is per germ cell per generation of course. This means that among each 10 of us on the average there are 2 to 4 mutations which arose in the germ cells of our parents, even though our parents were given no irradiation or other special treatment. This then is the frequency of so called spontaneous mutation. Now far more frequent than the mutant genes that have newly arisen in the parental generation, the immediate parents are those with arose in earlier generations and have been handed down and which have not yet been eliminated from the population by causing death or failure to reproduce. The average frequency, F, of all the mutant genes present per individual of the population, for you and me, is easily calculated if we know My and P by simply multiplying them together. For example if My is 2 in 10, that is 2 new mutant genes arising among 10 individuals in each generation on the average and P is 40. That is each gene tends to persist for 40 generations on the average. Then an individual of any given generation must contain an average accumulation of as many mutations as have arisen over the past 40 generations. That is 40 times 2 over 10 or 8. This very rough estimate which I made 6 years ago happens to agree well with the figure 8 estimated a few months ago by Slatis in Montreal by a very different and more direct method. His method was based on the frequency with which definite homozygous abnormalities appeared among the children of marriages between cousins. This figure 8 by the way does not include most of the multitude of more or less superficial differences, sometimes conspicuous but very minor in the conduct of life whereby we commonly recognise one another. These minor differences probably arise seldom by mutation, yet become inordinately numerous because of the very high value of P, persistence, which they have. The figure 8 then includes the more major detrimental characteristics. We can’t draw an exact line of course. These characteristics, these 8 or more detrimental genes however, being nearly always heterozygous in us are only slightly developed and yet enough developed to give each one of us a pattern of idiosyncrasies. I think I’d like to make a diagram to give you a more graphic idea of this relationship. Suppose we have here some individuals of a population. They reproduce and form 10 more. This is a much simplified diagram. And of these 10, 2 have a new mutation, just arisen in the previous generation and that’s passed down. And it’s passed down for 4 generations because the persistence we suppose in this simplified diagram is 4. And the mutation frequency is 2 in 10. Then in the next generation there’ll be 2 more. And in the next 2 more and so on. And you can see that if we start with no mutations the number here is each generation, a vertical column. The number gradually rises until it becomes 8. Then it says there until mutation stops occurring. Of course in the big population it would keep on. And so it would become stable at 8. And F, if F is the number of mutations it will equal MP. But of course in our case P is 40, where did I slip up there, I didn’t want to represent 40 but only as a matter of fact 8, Here the average individual only has 4 out of 10. And if the persistence was 40, the average individual would himself contain 8. That’s alright, that makes that 8/10th for this case. And if we have 40 it becomes 8. Gives each of us 8. Now as the diagram shows each mutant gene must at last cause the extinction of its own line of decent. Not only the gene comes to an end but that individual and his descendents come to an end. And they’re replaced by others who are multiplying. And in that way that gene causes a frustrated life at that point, an unsuccessful life. Moreover, that gene caused a succession of slight disturbances in the intermediate generations before the final extinction. It is interesting to note that a slightly detrimental gene, one that persists for many generations, also causes one frustrated life, one unsuccessful life, just as a very detrimental gene does. Only it takes longer before it happens to do that. Moreover, the slightly detrimental gene, although on the average it causes each individual carrying it to suffer less, is handed down to a larger number of individuals. To a number of individuals which is the reciprocal of the amount of harm expressed in terms of the risk of extinction that it causes. And in this way the slightly detrimental gene does as much harm in the end as a fully detrimental gene, a lethal. Now although each of us may be handicapped very little by any one of these genes in heterozygous condition, the sum of all 8 of them causes a noticeable amount of disability ranging, varying in pattern from one of us to another. And felt more in our later years of course, we feel our disabilities. Altogether we see that the group of the 8 or more, or less genes gives us a risk of premature death of roughly 20% or 1 in 5. Greater than that which an ideal normal man who is of course non existent, would have. Now these numbers are of course only approximations to give you an idea of the order of magnitude. Besides, the frequency F which is called the equilibrium frequency exists only when conditions for gene elimination and for mutation frequency have remained stable for many generations. Because over many generations as many mutations must arise per generation as are eliminated giving us stable value of F. Just as in the law of mass action in chemistry, a stable amount of a substance depends upon the same amount being destroyed as produced. But if the mutation rate changes, this again is like the law of mass action in chemistry. As for example by the application of radiation or if the persistence changes because of environmental conditions that cause mutant genes to have a more or a less harmful affect than before. Then the product MP assumes a new value. That means that there will be a new equilibrium level of F if the new values of My and P continue long enough. But it will be a long time before this new equilibrium is attained. Theoretically it’s never reached. Thus in our diagram we see that with P equals 4, it will take 4 generations before this equilibrium number is attained. This keeps increasing for 4 generations, equal to P equals 4. The actual case is more complicated because P doesn’t have a fixed value. Some genes are a little more and some less, some are much more and so it’s spread out. With P equals 40 on the average it would take something like 40 generations or about 1,000 to 1,200 years in man to get near an equilibrium value of F. And after only 20 generations or 500 or 600 years the equilibrium would be only about half reached. Let’s now see how a given dose of ionising radiation would affect the population. Radiation induces mutations similar to the spontaneous ones. At a frequency that’s linearly proportional to the dose of ionising radiation received by the germ cells. In no matter how long or short a time that’s been delivered. Now Russell’s data on mice, the organism studied in this respect which is nearest to man, show that it would take about 40 R/units, 40 R of radiation to produce mutations at a frequency equal to the natural frequency. Since we have estimated the spontaneous mutation frequency to be 2 mutations per individual that is to be 2 mutations in each 10 individuals at a minimum estimate. Then a dose at 40R by adding 2 induced mutations to these 2 spontaneous ones would result in a total frequency of 8 mutations among 10 individuals. That is the rate would be doubled. Yet the mutant gene content of the individuals being 8 per individual to begin with would be raised only from 8 to 8.2. An increase of only 2½% by this 40R in the next generation. This effect on the population would ordinarily be too small to be noticed. In causing decreased vigour or decreased size or increased mortality, or morbidity or frequency of abnormalities. One must remember in this connection that the error of any mean value for such characteristics is very large. Not only because of the great genetic differences between the individuals of the population. But because environment too is a source of differences in the expression of their inherited traits. And because one often gets determinate differences in environment between 2 groups that are compared. This explains why even Hiroshima survivors who had been near the blast and who may have received several hundred roentgens showed no statistically significant increase in genetic defects among their children. However, the offspring of American radiologists who probably got about the same amount over their life of radiation as the people at Hiroshima near the blast did in the studies of Macht and Lawrence just published, show a statistically significant increase in abnormalities among their children. A small but significant increase. Yet even though they do not show statistically that mutant genes are produced and they do take their toll in the end of genetic extinctions. But because of the value of P being so large, this toll is spread out over more than 1,000 years and so it’s quite small in any one generation, relatively. Actually, the most damage is done in the first generation after exposure. Because gradually the mutant genes die out. Contrary to common opinion which holds that later generations would show more affect. How much damage would be done in the first generation we can find in this way. If 40R were received then you have .2 new extra additional mutations received per individual. But since the persistence, P is 40, only 1/40th of those will cause extinction in any one generation, for example in the first generation. And therefore only 1/40th of .2 or 1 in 200 meet with extinction. It means that 1 in 200, ½ of 1% of the individuals of the first generation are killed. In other words in the population of 100 million it would be 500,000 in the first generation. Spread out over all the generations you multiply it by 40 and you find that there were 20 million. There will have been 20 million extinctions in a population of 100 million. Moreover, those are only the extinctions, the disabilities found in intermediate generations will of course be far more numerous. And yet in spite of this the amount of deterioration in the population as a whole is relatively very little. The situation would be very different if a doubling of the mutation frequency were carried out repeatedly by irradiating the population in each generation for a period comparable with P, say 1,000 years. For in that case F would gradually creep upwards towards the new equilibrium value proportional to the doubled mutation frequency. And after 1,000 years or so F would have been changed from 8 to about 16 by the 40R received over these many generations. Along with this double mutation frequency there would be a corresponding increase in the amount of disability manifested among the individuals of the population. And in the frequency with which they met genetically occasioned extinction. It is possible that this situation unlike that caused by only a single generations doubled mutation frequency would really be ruinous to a human population. For in man a given rise in mutation frequency is more dangerous than in most species. For the very low rate of multiplication of man does not allow nearly as rapid a rate of elimination per generation of detrimental mutant genes as in most species. And under modern civilised conditions this multiplication rate is reduced much more still. While at the same time the pressure of natural selection for the time being at least, in modern times is greatly reduced through the artificial saving of lives. Under these circumstances a long continued doubling of the mutation frequency by something like 40R per generation might call for a higher rate of elimination than the population could tolerate. This would mean in the long run the continued deterioration of the population in its gene content. More and more accumulation of mutant genes. And at last its diminution in numbers until finally total extinction ensued. We do not at present however have nearly enough knowledge of the strength of the various factors to pass a quantitative judgement as to how high the critical mutation frequency would have to be and how low the levels of multiplication and selection to bring about this denouement. We can only see that danger lies in this direction and ask for further study of the whole matter. Let us now consider the effects of nuclear explosions. As for test explosions, test explosions at the rate at which these have been carried on over the past 4 years, over the past year. They have been estimated to cause an approximate doubling of the background radiation of about 1/10th R per year. The background radiation we estimate causes about 6 to 12% of the spontaneous mutations in man. The others come from chemical causes. Therefore, a doubling of the background radiation would cause a 6 to 12% rise in the mutation frequency. Although this if continued does mean a very large absolute number of mutations per generation in the whole world population. About a million extinctions per generation caused by the test explosions in the whole world if they were continued at this rate. Nevertheless, its effect relatively to the whole population, the whole mutant gene content is extremely small. Atomic warfare presents a much more serious picture. In regions remote from the explosions such as the southern hemisphere might be it has been reckoned by Rotblat and by Lapp in the May and June issue of the bulletin of the Atomic Scientists that a hydrogen uranium fission fusion fission bomb like the ones recently tested in the Pacific would deliver an effective dose of about .04R throughout the whole period of its radio active disintegration, many years. Thus 1,500 such bombs used in war would deliver about 60R. That is to regions remote from the immediate fall outs. And so would approximately double the mutation frequency of the immediately exposed generation. In the regions subject to the more immediate fall outs, pattern bombing could have resulted in practically all populace areas receiving several 1,000 roentgens of gamma radiation. Even persons well protected in shelters during the first week might subsequently be subjected to a protracted exposure fading only very slowly and adding up to some 2,500 roentgens. You can look up Lapp, the article I’ve already referred to for that. Moreover, this estimate fails to take into account the soft radiation, alpha and beta from inhaled and ingested materials which under some circumstances as yet insufficiently dealt with in open publications may become concentrated in the air, water or food and find fairly permanent lodgement in the body. And some of them may there become concentrated also. Now although 400 roentgens is the semi lethal dose, that’s killing half of its recipients if received within a short time. A much higher dose can be tolerated if spread out over a long period of time. Thus a large proportion of those who survive and reproduce such fall outs may have received a dose of some 1,000 to 1,500R or even more. This would cause a 12 to 40 times rise in the mutation frequency of that generation. Not 12 to 40% understand, 12 to 40 times. If the mutant gene content is already because of P being 40, about 40 times the spontaneous mutation frequency, then the artificially induced mutation frequency here by adding to the germ cells another contingent of mutation genes. In fact the detrimental effect would be considerably greater than that indicated by these figures because the newly added mutant genes unlike those being stored at an equilibrium level would not yet have been subjected to any selective elimination in favour of the less detrimental ones. It can be estimated that this circumstance might cause the total detrimental influence of the newly induced genes to be twice as strong for each one on the average. As for each of the old stored so to speak genes. Therefore the increase in detrimental affect caused by the fall outs would be between 60 and 200%. Owing to these circumstances, an effect would be produced by this exposure to this one generation similar to that of a doubled accumulation of genes such as we saw would follow from a doubled mutation frequency only after about 1,000 years of its continued repetition when a new equilibrium level of accumulation had been approximated. Thus offspring of the fall out survivors might have genetic ills, twice or even 3 times as burdensome as ours. Yet at the same time the material and social disruptions occasioned by the war would enormously reduce the ability of the population to cope with and to compensate for these ills by means of medicine and all the other artificial aids to living on which we have come to depend so largely today. The worst of the matter is that this enormously increased genetic load, even though produced by a rise of the mutation frequency lasting little more than one generation, would be by no means confined to just 1 or 2 generations. Here is where the inertia of mutant gene content which in the case of a moderately increased mutation frequency works to retard, to delay and spread out, and so to soften the impact of the produced mutations, now shows the reverse side of its nature, its extreme prolongation of the effect. That is the gene content is difficult to raise. But once raised it is equally resistant to being reduced. In consequence the situation will for centuries resemble that in which an equilibrium had been attained with a mutation frequency that had been long continued at a level 2 or 3 times as high as the present one. Supposing the average content of markedly detrimental genes per person to be only doubled from 8 to 16, it can be reckoned that more than 50% of the population would come to contain a number of these mutant genes. When we consider how much we of today are already troubled with ills of partly or wholly genetic origin, especially as we grow older, the prospect of so great an increase in them is far from reassuring. It is fortunate in the long run that sterility and death ensue beyond a chronically administered dosage level of 1 or 2,000 roentgens. Because the frequency of mutations received by the descendents of an exposed population is in this way prevented from rising much beyond the amount that we have just now considered. This being the case it is probable that the offspring of the survivors, even though so considerably weakened genetically, would nevertheless, some of them be able to struggle through and re-establish a population that could continue to survive. Yet supposing that the population is able to re-establish its stability of numbers within say a couple of centuries, what price would the later generations have to pay in terms of premature death and failure to reproduce caused by the induced mutations? If in accordance with the evidence previously given, 40R admitted to produce .2 newly arisen mutant genes per person, then 1,000R must on the average add 5 mutant genes to each person’s composition. All of these 5 genes must ultimately lead to genetic extinction in a subsequent generation. But if to be conservative we suppose that 2 to 3 genes on the average combine in causing extinction. By their synergistic action we reach the conclusion that in a population whose numbers remain stable after the first generation following the explosions, there will be about 2 cases of premature death of failure to reproduce occurring in subsequent generation or other. For each first generation offspring of an exposed individual. That is if there had been 100,000 first generation offspring, there’d be 200,000 subsequent deaths in sub generation. The same in terms of millions. If however the descendents multiply so as in a century or 2 to re-establish a population equal in number to the original population, then since the great majority of the extinctions occur in more remote generations their number will be multiplied along with the number of the whole population. And so the number of genetic deaths or extinctions will become approximately twice as large altogether as the number of persons constituting the re-established population size of any one generation. The future extinctions would in this situation be several times as numerous as the deaths that have occurred in the directly exposed generation. If 70 million people had been killed at the time of the explosions then something like let’s say 2 or 300 million will be killed in future generations. At the same time the people suffering from more or less ... Even though we admit it to being probably that mankind would ultimately revive, let us not make the all too common mistake of gauging whether or not any given or proposed exposure to radiation is genetically permissible merely by the criterion of whether or not humanity at large would be completely destroyed by it. The instigation of atomic war or indeed of any other form of war can hardly find a valid defence in the proposition. Even though true that it will probably not wipe out the whole of mankind. It is by the more exacting standard of whether individuals are harmed, not by the criterion of whether mankind in general will all be wiped out, that we should judge the propriety of our other present day and proposed practices that may affect the human genetic constitution. We have to consider in this connection for one thing, the amount of radiation which the population should be allowed to receive as a result of the peace time uses of atomic energy in polluting that derived from atomic waste. How much effort in convenience of money are we willing to expend in the avoidance of one genetic extinction, of one line of decent of a person. One frustrated and other partially frustrated lives, not to be seen ever by us. Will we accept the present official view that the permissible dose for industrially exposed personnel may be as high as .3R per week, that is 300R in 20 years. A dose which would lead such a worker to transmit somewhere between ½ and 1½ mutations per offspring conceived after that time. Exactly the same questions apply in medical practice. The United States public health survey conducted 3 years ago showed that at that time Americans were receiving a skin dose of radiation averaging about 2R per person per year from diagnostic examinations alone. Of course only a small part of this would have reached the germ cells. But if the relative frequencies of the different types and amounts of exposure were similar to those in studies recently carried out in British hospitals by Stanford and Vance, we may calculate from their data that the total germ cell dose to the Americans was about 1/30th of the total skin dose. That is in this case about .06R per person per year. This is about 12 times as much as the dose that had previously been estimated to reach the reproductive organs of the general population in England. However America is notoriously lighting the wave of the future in regard to the employment of x-rays. And it is still engaged in rapidly expanding their use while other countries are following as fast as they can. Now this dose of .06R per year, per person is of the same order of magnitude but twice as large as the annual dose received in the United States over the past 4 years, per year from all nuclear tests, explosions. It is my personal opinion that at the stage of international relations at which we have been during the past several years, these nuclear tests have been justified as warnings and as defensive preparations against totalitarianism. Although it is to be hoped that this stage is now about to become obsolete. On the contrary however I cannot find justification for the large doses received from medical irradiations. Which as I have just shown you are about equal or more in amount. For comparatively little thought in convenience or expense would be involved in the routine provision of shielding over the reproductive organs of individuals who may later reproduce. My experience is that when they ask for such a shield, in our country at least, they’re simply laughed at and it’s refused. And little thought or inconvenience in making many obvious and easy rearrangements of the irradiations so as to reduce the dose being received by the reproductive organs and other parts not being examined. I won’t go into the details of that, it’s very simple most of the radiologists as an investigation by Sonnenblick has shown hardly, they don’t know what dose they’re delivering at all, not one in 100 knew. Moreover the widespread present day procedures of intentional heavy irradiation of the ovaries to induce ovulation in infertile women and the heavy irradiation of the testes to provide an admittedly temporary means of avoiding pregnancies should hence forth be regarded as malpractice, in my opinion. We must remember that atomic tests and possibly atomic warfare may be dangers of our own turbulent times only. Whereas physicians will in some form always be with us. It is easier and better to establish salutary policies with regard to any given medical practice early than late in its development. If we continue neglectful of the genetic damage from medical irradiations, the dose received by the germ cells will tend to creep higher and higher and to be joined by a rising dose received from industrial applications of radiation and of the energy from radioactivity. For the industrial powers that be will tend to take their cue, their advice in such matters from the physicians as they have done, not from the biologists, even as the military and administrative powers that be do today. It should be our generation’s concern to take note of this situation and to make further efforts to start the expected age of radiation, if there is to be one, off in a rational way as regards protection from this insidious agent so as to avoid that permanent significant raising of the mutation frequency which in the course of ages could do even more genetic damage than an atomic war. But radiation is by no means the only agent capable of greatly increasing mutation frequency. Various organic substances such as the mustard gas groups. Some peroxides, epoxides, carbonates, triazine, ethanol sulphate, formaldehyde and so on can raise the mutation frequency about as much as radiation. The important practical question is to what extent may man be unknowingly raising his mutation frequency by the ingestion or inhalation of such substances or substances which after entering the body may induce or result in the formation of mutagens, that is, mutation producing substances that penetrate to the genes, the germ cells. Although some of the known mutagens such as the mustards would seldom be encountered in daily life under normal conditions, others such as some peroxides would enter the body more frequently or would even be manufactured there. In the later cases however there are often efficient means of destruction, channelization or disposal in the body. Such as catalase and the cytochromes that ordinarily greatly reduce the opportunity of these substances to attack the genes. Yet under certain circumstances, more especially with certain combination treatments these protective mechanisms may not work. As yet far too little is known of the extent to which our genes under modern conditions of exposure to unusual chemicals are being subjected to such mutagenic influences. Other large differences in the frequency of so called spontaneous mutations have been found in my studies on the mutation frequency characterising different stages in the germ cycle of drosophila. Moreover some evidence has been introduced by Haldane dealing with data of Mørch and others that the germ cells of older men have a much higher frequency of newly arisen mutant genes than those of young men. If this result, which has been found not to hold for the fruit fly drosophila should be confirmed for men, there’s some doubt about it. It might prove to be more damaging genetically for human population to have the habit of reproduction at a relatively advanced age than for its members to be regularly exposed to some 50R of ionising radiation in each generation. It’s evident from these varied examples that the problem of maintaining the integrity of the genetic constitution is a much wider one than that of avoiding the irradiation of the germ cells, since other influences may play a mutagenic role as great or greater. Now since F equals My P and P, the persistence is the reciprocal of the rate of elimination of mutant genes. It is evident that the rate of elimination is just as important as the mutation frequency in the determination of the human genetic constitution. If one prescribes some more distinctive term, one may say selected, than elimination, one may say selective elimination. Selective multiplication or simply selection. The importance of this factor is seen in the fact that the ancestors of men and mice, in them much the same mutations must have occurred in the original common ancestors, yet the different conditions of their existence. The ever more mousey living of the mouse progenitors and the manlier living of the pre-men caused a different group of genes to become selected from out of their common store. A very distinctive feature of the type of selection operating among human beings living under the conditions of our modern industrial civilisation is the tremendous saving of human lives that under primitive conditions would have been sacrificed. This is accomplished in part by medicine and sanitation, but also by the abundant and diverse artificial aids to living supplied by industry and widely disseminated through the operation of modern social practices. So small is now the proportion of those who die prematurely that it must be considerably below the proportion who would have to be eliminated in order to keep the rate of elimination of mutant genes equal to the rate of their origination by mutation. Surely less than 2 in 10 for elimination. We know in America the great majority live to 65, 70, 69 anyway for men, over 70 for women. In other words many of the saved lives must represent persons who under more primitive conditions would have died as a result of genetic disabilities. Moreover among those who survive there does not seem to be much selective influence in hindering the marriage and multiplication of the genetically less capable. In fact there are certain oppositely working tendencies. Therefore it is probably a considerable underestimate to say that a half of the detrimental genes that under primitive conditions would have met genetic extinction, today survive and are passed on. Calculating on the basis of this conservative estimate we find that in some 10 generations, 250 to 300 years, the genetic affect would have become much like that of applying 200 to 400 roentgen units all at once, as with the offspring of the most heavily exposed Hiroshima survivors. Of course as time goes on the rate of rise in accumulation towards a new equilibrium level of F falls off more and more from linearity until at last at equilibrium the curve is again flat. However in the situation we are considering the simultaneous advance of techniques would tend to raise the equilibrium level ever higher. And would thereby foster continued accumulation. In this way the passage of 1,000 years would be likely to result in the population as heavily loaded with mutant genes as though it were derived from the survivors of hydrogen uranium fission fusion fission bomb fallouts. And 2,000 years would continue the story until the system fell of its own weight or became reformed. The process just depicted is a slow invisible, secular one. Like the damage resulting from many generations of exposure to overdoses of diagnostic x-rays. Therefore it is much less likely to gain credence or even attention than the sensational process of being overdosed by the fallouts from bombs. This situation then ever more than that of the fallouts calls for basic education on the part of the public and the publicists before they will be willing to reshape their deep rooted attitudes and practices as required. It is necessary for humanity to realise that a species rises no higher genetically and stays no higher than the pressure of selection forces it to do. And to any relaxation of that pressure, it responds by sinking correspondingly. It will in fact take as much rope in sinking as we play out to it. The policy of saving all possible genetic defectives for reproduction must if continued eventually rob us of the very important benefits now enjoyed by which afflictions of generic origin today have their effects ameliorated and are often prevented from causing genetic extinction. The reason for this is evident as soon as we consider that when by artificial means a moderately detrimental gene is made less detrimental, its frequency will gradually creep upward toward a new equilibrium level at which it is finally being eliminated anyway. At the same rate as that at which it had been eliminated originally. Namely at the rate at which it arises per generation by mutation. This rate of elimination being once more just as high as before medicine began will at the same time reflect the fact that as much suffering and frustration will be existing in consequence of that detrimental gene as existed under primitive conditions. I explained how a slightly detrimental gene causes as much trouble in the end as a more detrimental one because it affects more individuals. Thus with all our medicine and other techniques we will be as badly off so far as many of the considerable group of ailments which, of genetic origin are concerned as when we started out. Not all genetic ills however would be simply made less detrimental, some of them would be made not detrimental at all under the circumstances of a highly artificial civilisation in the sense that they were unable to persist indefinitely and thus to become established as the new norm of our descendants. The number of these disabilities would increase in abundance up to such a level that no more of them could be supported and compensated for by the technical means available and by the resources of the social system. The burden of the individual cases up to that level would have become largely shifted from given individuals themselves to the whole community, through its social services, a form of insurance. Yet the total cost would be divided among all individuals. And that cost would keep on rising as far as it was allowed to rise. Ultimately then in that utopia of inferiority, in the direction of which we are at the moment headed, people would be spending all their leisure time in having their ailments nursed and as much of their working time as possible in providing the means whereby the ailments of people in general were cared for. Thus we should have reached the acme of the benefits of modern medicine, modern industrialisation and modern socialisation. But because of the secular, the very long time scale of evolutionary change and the inertia which retards changes in gene frequency this condition would come upon the world with such insensible slowness that, except for a few long haired cracks who took genetics seriously and perhaps some archaeologists, no one would be conscious of the transformation. If it were called to their attention they would be likely to rationalise it off as progress. It is hard to think of such a system not at length collapsing as people lost the capabilities and the incentives needed to keep it going. Such a collapse could not be into barbarism anymore however since the population would have become unable to survive primitive conditions. Thus a collapse at that stage would mean annihilation, unless there was still primitive people living in some corner of the world many in a preserve. But we’d be too humanitarian for that. There is however an alternative policy open to mankind and I am hopeful that before too late it will be adopted. This alternative policy by no means abandons modern techniques or recommends a return to the fabulous golden age of noble savages or even of rugged individualism. It makes use of all the science, skills and genuine arts we have to ameliorate, improve and ennoble human life. And so far as is consistent with its quality and well being to extend its quantity and range. Medicine, especially that of a far seeing, preventive and still better, that of a promoting kind, seeking actively to foster health, vigour and ability becomes on this policy more developed than ever. Persons who nevertheless have defects would certainly have been treated and compensated for it. So as to help them to lead useful, satisfying lives. But, and here is the crux of the matter, those who were relatively heavily loaded with genetic defects would consider it their obligation. Even if these defects had been largely counteracted by medicine to refrain, to keep from transmitting their genes. Except where such unusually valuable genes were also present in them that the gain for the descendents was likely to outweigh the loss. Through the adoption of such an attitude towards genetics and reproduction, an attitude seldom found as yet. And by this means only unless with Doctor Stanley and his colleagues we learn to artificially change the gene in the ways that we want to. Otherwise through this means only will it be possible for future generations indefinitely to maintain and to extend the benefits of medicine, of technology, of science and of civilisation in general. Anything else is to sell ourselves to the genius of decay for the satisfaction of a vain glorious desire for offspring who may for a few evanescent generations perpetuate our petty idiosyncrasies. It is true that for evolutionary changes in outlook, motivation and procedure are required before such a policy can be effective. The heart of these changes is the adoption of the viewpoint that whether or not a child should be produced in the given case or to be decided primarily according to the good of the next and succeeding generations and of the child himself, rather than for the edification or glorification of that child’s parents or ancestors. Nevertheless, no southern revolution in this respect is necessary or likely. It is sufficient for more and more persons gradually to come around to the more rational attitude. With the advance of realistic education, if as we must hope it will resume its advance despite its present decline in some of the most literate countries, there should come a better realisation of man’s place in the great sweep of evolution and of the risks and the opportunities genetic as well as non genetic which are increasingly opening to him. The tremendous realities of insensible, secular, long drawn out changes will be brought home to child and youth by means of vivid dramatised portraits. And if teaching does its duty that youth will become imbued with a will to act as a conscious agent of his species in its advance against outer and inner nature. Whether or not his personal genes for the most part like those of everyone else, are to go on, will then be a relatively minor matter to him. So long as he can foster the handing down of good genes, if possible better genes. He will also find gratification in helping to provide conditions where in these genes will be given the opportunity in their corporeal expressions of flowering ever more rich. It is evident from these considerations that the same change in view point that leads to the policy of voluntary elimination of detrimental genes would carry with it the recognition that there is no reason to stop short at the arrested norm of today. For all goods genetic or otherwise are relative. And so far as the genetic side of things is concerned, our own highest fulfilment is attained by enabling the next generation to receive the best possible genetic equipment. What the implementation of this view point involves by way of techniques on the one hand and of wisdom in regard to values on the other hand is too large a matter for treatment here. Nevertheless, certain points regarding the genetic objectives to be more immediately sought do deserve our present notice and when then I’m through, won’t take long. For one thing the trite assertion that one cannot recognise anything better than oneself or in imagination rise above oneself is merely a foolish vanity on the part of the self complacent. On the other hand men’s prejudices are so deep seethed. Men’s imaginations are so limited. And the world is so complex and full of pitfalls that it is important to guard against the setting up of far flung programs for the attainment of this or that peculiarity that happens to be in vogue. Such superficialities of mankind as colouration, size or features and so on are 2 disputations under modern conditions of too little importance for us to allow them to distract our attention from the more important objectives. Among these all around health and vigour, joy of life and longevity are unquestionable to be solved. Yet they are far from the supreme aims. For these aims we must search through the most rational and humane thought of those who have gone before us and integrated with the thought based on our present vantage point of knowledge and experience. In the light of such a survey I think it becomes clear that man’s paramount, his most important present requirements are on the one hand a deeper and more integrated understanding, better intelligence all around. And on the other hand a more heartfelt keener sympathy, that is a deeper fellow feeling leading to a stronger impulse to cooperation, more in a word of love. It is wishful thinking on the part of some psychologists to assert that these qualities result purely from condition or education. For although such factors certainly do play vital roles in the development of these traits, nevertheless homo sapiens wherever he occurs is relatively to other organisms both an intelligent and a cooperating animal, even though cooperating in only small groups. It is these 2 complex genetic characteristics working in combination, and only in combination, and serviced by the deftness of his hands which above all others have brought man to his present state. Moreover, there still exist great diverse and numerous genetic differences in the biological basis of these traits within any human population. Although our means of recognition of these genetic differences are today very faulty and tend to confound differences of genetic with those of environmental origin. Nevertheless, these means can be improved. And there’s work being done to improve it. Thus we can be enabled to recognise our betters. Yet even today our techniques are doubtless more accurate than the trials and errors whereby after all nature did manage to evolve us up to this point where we became effective in counteracting nature. Certainly then it would be possible if people once became aware of the genetic road that is open to them for a population to be brought into existence. Most of whose members were as highly developed in regard to the genetic basis of both intelligence and social behaviour as are those scattered individuals of today who now stand highest in either separate respect. This would be really lifting us a long way by our boot straps so to speak. Perhaps after this great advance had been made, men could begin to think constructively. Not only of ways of progressing still further in these same directions but also of the development of other accessory genetic features that would enhance their lives. If the fear of the misuse of nuclear energy awakens mankind, not only to the genetic dangers confronting him, but also to the genetic opportunities then this will have been the greatest peace time benefit that radioactivity could bestow upon us. Thank you. Applause.

Hermann Joseph Muller voicing his fears concerning genetic damage in the expected age of radiation
(00:40:43 - 00:47:46)

 

Nearly thirty years later, nuclear physicist and Nobel Laureate Rosalyn Yalow expressed a totally different view, blaming the public’s irrational fear of radiation at any level on headlines that never caught up with the facts:

 

Rosalyn Yalow disapproving the public’s irrational fear of radiation
(00:29:32 - 00:33:35)

 

The current attitude to radiation and radioactivity is still laced with fear, particularly regarding nuclear power plant disasters, protection against natural UV radiation from the sun and leakage of radioactive waste. The use of radiation in medicine is supported by the term ALARA, an acronym for “As Low As Reasonably Achievable”. The benefits of modern-day life-saving medical procedures greatly outweigh the small risks of radiation use. In these respects, the role of scientists as effective communicators is considerable. “As scientists we must be prepared to discuss with the public why we cannot survive in a no-risk society.” Yalow expressed this sentiment in Lindau over three decades ago, and it is still relevant today.

Footnotes

https://assets.nobelprize.org/uploads/2018/06/chadwick-lecture.pdf?_ga=2.61450858.794804564.1536232660-344762665.1535026955
http://chandra.harvard.edu/tech/
http://science.sciencemag.org/content/102/2659/608.2
https://www.aps.org/publications/apsnews/200803/physicshistory.cfm
https://www.aps.org/publications/apsnews/200705/physicshistory.cfm
https://www.europhysicsnews.org/articles/epn/pdf/2011/05/epn2011425p18.pdf
https://www.healio.com/hematology-oncology/news/print/hemonc-today/%7B2df0dfa1-ce57-490a-8bea-6533f4a89f84%7D/the-shoe-fitting-fluoroscope-a-little-known-application-of-the-x-ray
https://www.lindau-nobel.org/enrico-fermi-and-the-dawn-of-the-nuclear-age/
https://www.lindau-nobel.org/roy-glauber-and-his-time-in-los-alamos/
https://www.lindau-nobel.org/the-manhattan-project-life-in-los-alamos/
https://www.mediatheque.lindau-nobel.org/research-profile/laureate-soddy#page=all
https://www.mskcc.org/blog/hot-times-radium-hospital-history-radium-therapy-msk
https://www.nobelprize.org/prizes/chemistry/1935/joliot-curie/facts/
https://www.nobelprize.org/prizes/physics/1939/lawrence/facts/
https://www.nobelprize.org/prizes/themes/marie-and-pierre-curie-and-the-discovery-of-polonium-and-radium/
https://www.nytimes.com/1998/10/06/science/a-glow-in-the-dark-and-a-lesson-in-scientific-peril.html
http://www.world-nuclear.org/information-library/current-and-future-generation/nuclear-power-in-the-world-today.aspx
Bryson, B. (2003) A Short History of Nearly Everything. Doubleday.
Carlsson, S. (1995) A Glance at the History of Nuclear Medicine. Acta Oncologica 34 (8), 1095-1102.
Connell, P.P., Hellman, S. (2009) Advances in Radiotherapy and Implications for the Next Century: A Historical Perspective. Cancer Research 69 (2).
Fernandez, B. (2013) Unravelling the Mystery of the Atomic Nucleus. A Sixty Year Journey 1896 – 1956. English version by Georges Ripka. Springer Science + Business Media, New York, NY.
Feynman, R.P. and Leighton, R. (1985) Surely You’re Joking Mr Feynman! Vintage, London.
Jaccard, M. (2005) Sustainable Fossil Fuels: The Unusual Suspect in the Quest for Clean and Enduring Energy, pp.101-111. Cambridge University Press, New York, NY.
Rogers, J.D. (2013) The Neutron’s Discovery – 80 Years On. Physics Procedia 43, 1-9.


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