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Fermi postulates the beta-decay theory: Fermi's interaction
Hans Bethe Scientist
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Well, Pauli's idea was taken up by Fermi, who produced a beautiful and very convincing theory which is... which still remains right to the present day, the first point of which was that electron and neutrino are... do not exist in the nucleus but are formed at the moment of disintegration, just like a quantum, like quantum is formed at the moment when the atom makes a transition, it isn't in the atom beforehand. And so you don't need to assume any electrons in the nucleus, electrons are newly formed, two particles come out simultaneously. He used the Dirac mechanism for creating particles and so you have the emission of an electron and a neutrino. Well, that seemed very convincing, and indeed is still right today, but there was the question - could you ever observe a neutrino? So Rudi Peierls and I thought about that and came to the conclusion there are two possible ways a neutrino could show itself. It might have a magnetic moment, but that seemed rather far-fetched since it had no charge. In that case you could observe ionization and one little paper I wrote was... discussed just what a magnetic neutrino would do when going through matter. But more likely it did not have a magnetic moment, and in that case the only way how you could observe a neutrino is if the neutrino caused in turn the inverse of a beta decay, that is, the neutrino would go into the nucleus; an electron would come out. And at that time it seemed just incredibly unlikely that one could ever observe that. Fortunately nature knows its way better than we did, and nuclear power was invented and in a nuclear power reactor you get just incredible numbers of neutrinos produced all at one time and at one point, so that later on, well after the war, it was possible to observe neutrinos causing electrons, ejecting electrons from... from a nucleus. But Peierls and I said 'Well, if this is the only way a neutrino can show itself, it is likely that it will never be observed.' So we were quite right saying that this is the only way how a neutrino can be observed, but we were fortunately quite wrong saying that it can never be observed.

The late German-American physicist Hans Bethe once described himself as the H-bomb's midwife. He left Nazi Germany in 1933, after which he helped develop the first atomic bomb, won the Nobel Prize in Physics in 1967 for his contribution to the theory of nuclear reactions, advocated tighter controls over nuclear weapons and campaigned vigorously for the peaceful use of nuclear energy.

Listeners: Sam Schweber

Silvan Sam Schweber is the Koret Professor of the History of Ideas and Professor of Physics at Brandeis University, and a Faculty Associate in the Department of the History of Science at Harvard University. He is the author of a history of the development of quantum electro mechanics, "QED and the men who made it", and has recently completed a biography of Hans Bethe and the history of nuclear weapons development, "In the Shadow of the Bomb: Oppenheimer, Bethe, and the Moral Responsibility of the Scientist" (Princeton University Press, 2000).

Tags: Enrico Fermi, Wolfgang Pauli, Rudi Peierls

Duration: 4 minutes, 5 seconds

Date story recorded: December 1996

Date story went live: 24 January 2008