Schematic diagram of chain reaction from fission, neglecting effect of neutron speed

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A schematic rather than a photograph, this 1948 print lays out how a single fission event can set off a chain reaction in which each split nucleus releases neutrons that go on to split others. Its caption says it neglects the effect of neutron speed, a simplification that let its designers focus on the basic branching pattern rather than the finer physics of how fast neutrons interact with uranium. Diagrams of this kind were common in the years after the Second World War, when the public and policymakers were trying to grasp how nuclear energy and weapons worked. The Library of Congress holds it among its prints and photographs, where it documents the way technical ideas were explained to a general audience in the early Atomic Age.

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