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Help from the British, and the 'Christy Gadget'


The implosion design of the plutonium atomic bomb
Hans Bethe Scientist
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In the middle of the Los Alamos experience, it was discovered by Segrè that plutonium, in fact, the isotope plutonium-240, had an exceedingly high spontaneous rate of fission. It fissions at a rate that was so fast that our chosen method of assembling a bomb, namely by shooting one piece of material into another target would not work. On the way of... on the flight from the gun to the target, the fissile material would already began... become critical and begin reacting, and we would get a very low yield, a fizzle. So another method of assembly had been suggested by Neddermeyer; namely to take the shell of fissile material and surround it by explosives. In that case you could get speeds about 10 times higher than you could get from a gun and you would have an implosion. So while in the beginning of the project, nuclear physics was the determining factor in the question of nuclear weapons, it now turned out that the really important thing was to study the implosion. And we did that, both analytically and numerically by means of the IBM machines, the latter being under Feynman's direction.

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: Los Alamos, Seth Neddermeyer, Emilio Segrè, Richard Feynman

Duration: 2 minutes, 26 seconds

Date story recorded: December 1996

Date story went live: 24 January 2008