Rudolf Mößbauer (1988) - The solar neutrino problem

Rudolf Mößbauer (1988)

The solar neutrino problem

Rudolf Mößbauer (1988)

The solar neutrino problem

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In his first three neutrino lectures at the Lindau Meetings, Rudolf Mößbauer described his experimental project to detect a possible non-zero neutrino mass through the observation of neutrino oscillations. As a source for neutrinos, he used nuclear fission reactors in France and Switzerland. At the time of the present lecture, these experiments were finsihed and Mößbauers interest had moved to using a much larger source of neutrinos, the sun. In the first part of the lecture, which gives the background to his involvement in a new experimental collaboration, Mößbauer describes what is called the standard solar model and how the neutrinos are created in nuclear fusion reactions in the interior of the sun. He also gives a very nice short history of the concept of neutrino particles, which derives from Wolfgang Pauli’s attempts to understand the continous energy spectrum of electrons emitted in radioactive decay and in which, among others, Lise Meitner was involved. Mößbauer also puts forward the hypothesis that the universe is filled with very low energy neutrinos, much like the cosmic background radiation discovered by Arno Penziaz and Robert Wilson. Since the detection of very low energy neutrinos is extremely difficult, he tells his audience of students and young researchers that finding a method to detect a cosmic neutrino background surely would lead to a Nobel Prize. As far as I know, this background radiation has so far (2012) not been detected, so there is still lots to do! Mößbauer then describes the so-called solar neutrino puzzle, by which was meant the fact that only one third of the expected neutrinos from the sun were ever detected during many years of experiments in the Homestake mine in the US. Finally, he describes a new project which would complement the Homestake measurements by looking for neutrinos of a lower energy. This new project, planned to start taking data in the beginning of the 1990’s, had been given the name GALLEX and was to be constructed in the Gran Sasso tunnel north of Rome. Mößbauer gives an inspired account of the problems in starting this new project, acquiring funding of about 20 million US dollars (too much for the low-energy committees, too little for the high-energy committees!), and buying about 100 tons of gallium chloride. In this amount of gallium chloride, about one gallium atom per day would be hit by a solar neutrino and thus transmuted into a radioactive germanium atom. Since the radioactive germanium atom would have a half-life of about 10 days, the 100 ton detector fluid would have to be washed trough every fortnight in order to find the radioactivity! Mößbauer shows pictures of the laboratory and the planned experiment and also explains what information could be gained from the measurements. Having listened to several lectures by Mößbauer, both recorded and in real life, I have seldom heard him be so enthusiastic! Anders Bárány

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