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Robert Serber, The Los Alamos Primer

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In 1938, Lise Meitner and collaborators discovered that the nuclei of certain heavy metallic elements, most notably uranium, are subject to fission: when bombarded with neutrons, they will sometimes absorb the neutron, becoming unstable and splitting into two smaller nuclei, releasing more neutrons, and much miscellaneous radiation, in the process. It was quickly realized that those new neutrons could trigger more fissions, and so start a chain reaction, which would grow exponentially until its fuel began to be exhausted, developing a tremendous amount of energy in moments. But stray neutrons are relatively common, and uranium, while rare, is still around, not having long since vanished in a puff of gamma rays. Why not? Well, for two reasons. First: not all uranium nuclei are fissile. The two principle sorts are the lighter U-235, and the heavier, much more common U-238. Only U-235 will fission at low energies; U-238 is more stable. Second: even if you got together purified U-235 and s

Robert Serber, The Los Alamos Primer The Bactra Review: Occasional and eclectic book reviews by Cosma Shalizi 57 The Los Alamos Primer The First Lectures on How to Build an Atomic Bomb by Robert Serber annotated by Robert Serber edited with an introduction by Richard Rhodes University of California Press, 1992 Technical Sweetness and Light (and Heat and Fast Neutrons) To make an atomic bomb, take a few kilos of plutonium, shaped into half spheres, in either hand and slap them together. Building a good bomb is harder. In 1938, Lise Meitner and collaborators discovered that the nuclei of certain

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