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The discovery of positrons


The synchrocyclotron and the betatron
Hans Bethe Scientist
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Almost 10 years later McMillan did skin the cat and found out that one could preserve synchronous orbits and focusing, by changing the frequency of the cyclotron and that hadn't been possible in 1936, but it was very possible in 1945 because in the meantime, radar had been developed at the MIT Radiation Lab, and so by the confluence of technical development and an ingenious inventor, this Synchrocyclotron was... was developed. It was invented at the same time in Russia by [Vladimir] Veksler and it was then built almost immediately after the war in Berkeley and was used very effectively by the Berkeley group including Panofsky. And at the same time another instrument was invented by Don Kerst at Illinois which was the Betatron in which electrons were accelerated, already having relativistic velocities, keeping the same orbit all the time. Then Macmillan and Veksler said 'Well one could combine these two and have a Synchrotron where... which was... betatron with changing frequency', which is nowadays the preferred method of accelerating particles to very high energy.

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: MIT Radiation Lab, Berkeley, University of Illinois, Edwin McMillan, Vladimir Veksler, WKH Panofsky, Donald Kerst

Duration: 2 minutes, 21 seconds

Date story recorded: December 1996

Date story went live: 24 January 2008