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Supernova shocks


More on supernovae, the gain point
Hans Bethe Scientist
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Now we had to understand this quantitatively. We had to understand how this really happened and Brown and I together with two students of Brown; Cooperstein and Baron, worked on this very assiduously for quite a long time and only over many years did it finally become clear. Indeed, the neutrinos go out, but there is unfortunately a reverse process, namely when you have dense matter then electrons are captured by the nucleus and that makes additional neutrinos, and so the energy which is in the electrons and generates thermal energy of the matter, again gets transformed into neutrinos which escape from the star without doing any good. Finally, in... oh I think '92 or so, it came to me that there is one place, one critical place where the energy given by the neutrinos gets to be bigger than the energy absorbed from the electrons, and I called that the Gain Point. And the gain point comes about because the Neutrino Flux, the energy flux of the neutrinos goes down as the square of the radius, one over the square of the radius. But the capture of electrons goes as the sixth power of the temperature, and the temperature goes down inversely as the radius, so the capture of electrons goes down as the sixth power of the radius. So there must be some point at which the gain from neutrino absorption gets bigger than the loss from electron capture. I call that the gain point, and outside the gain point now you get a net gain of energy by absorbing neutrinos. I wrote a joint paper with Jim Wilson on this problem, and then quite a number of papers by myself, and some with Brown.

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: James Wilson, Gerald Brown, Edward Baron, J Cooperstein

Duration: 3 minutes, 5 seconds

Date story recorded: December 1996

Date story went live: 24 January 2008