Gustav Hertz (1968) - Memories of James Franck and the Electron Scattering Experiments (German Presentation)

Gustav Hertz (1968)

Memories of James Franck and the Electron Scattering Experiments (German Presentation)

Gustav Hertz (1968)

Memories of James Franck and the Electron Scattering Experiments (German Presentation)

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Gustav Hertz participated in five of the Lindau Nobel Laureate Meetings and this is the last one. His earlier lectures had all been concerned with his more recent research interest in nuclear isotopes, but for this lecture he had chosen the story behind the 1925 Nobel Prize that was awarded to him and James Franck in 1926. It was not so unusual at that time, that a Nobel Prize was reserved from one year to the next. The same procedure was followed, e.g., for Max Planck and Albert Einstein. At the time of the Nobel awarded discovery made by Franck and Hertz, the 5 year younger Hertz was a PhD student with Franck in Berlin. At the time of the Lindau lecture, Franck had passed away and Hertz was 80+, but still going strong. He delivered the lecture at a sprinters speed, in a lively way with many jokes. As he told the story of the discovery of electron impact excitation of atoms, “it was mainly a task for the hands and not for the head”. With this he referred to the construction of the apparatus, which initially was planned to be used for studies of electrical discharges in gases. It was well known that a minimum electric potential was needed to get a flow of ions and electrons through the gas and this potential was identified with the ionization potential of the atoms. But when it was found that there was a stepwise increase in the electric current also below the ionisation potential, it was realized that this showed the quantized excitation of the atoms, just as predicted by the then recently published Bohr theory. In this way their “hands on” experiment became an important cornerstone for the “in heads” quantum theory and explains why their work was rewarded with a Nobel Prize!

Anders Bárány

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