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The deuteron disintegration theory disproved


Working on a theory of deutron disintegration
Hans Bethe Scientist
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Peierls and I went to Cambridge to discuss this with Chadwick and Goldhaber, which was very interesting. And Chadwick then said to the two of us 'Well, I bet you, you cannot make a theory of that.' So there was a five hour train trip back from Cambridge to Manchester and during that train trip Peierls and I solved the problem of the theory of this disintegration, and we then wrote a paper about that. Having... when we assumed I think we had thought of that before, and I believe also Heisenberg had thought of that, that the range of the forces between neutron and proton, the nuclear forces, must be very short, very short compared to the size of the deuteron, and that made it very easy to write down the wave function of the deuteron. In fact we could write it down on the train still, and it's beautifully simple and knowing that we could also solve the problem of the scattering of neutrons by protons that was being experimented on, and we calculated to start the cross section for that scattering was very closely related to the binding energy of the deuteron. And from that we calculated that the cross section should be about 3*10-24 cm2. 10-24 cm2 is called a Barn. For a nucleus it's the cross section as big as a barn, as one of my later colleagues at... at Cornell invented, and so we calculated 3 Barns. The unfortunate thing however was that people did [the scattering] experiments on it, many of them at Columbia University, and they found about 20 Barns instead of 3 Barns, and that 20 Barns was obtained even after Fermi had shown that there is a correction for the binding of the two deuterons in the molecule. The actual figure the experimenters had found was 50 Barns, but Fermi's correction brought it down to 20. So obviously our theory of this scattering was very beautiful but unfortunately wrong.

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: Cambridge, Manchester, Rudi Peierls, James Chadwick, Gerson Goldhaber, Werner Heisenberg, Enrico Fermi

Duration: 3 minutes, 8 seconds

Date story recorded: December 1996

Date story went live: 24 January 2008