Harold Agnew with the Plutonium Core

Harold Agnew saw the completion of the atomic bomb from start to finish. As a member of Enrico Fermi’s research team at the University of Chicago in 1942, Agnew witnessed the first sustained nuclear chain reaction, Chicago Pile-1. He worked in the Experimental Physics Division at Los Alamos from 1943 to 1945. While the Trinity test was being conducted, Agnew was already on his way to Tinian Island in the Pacific as part of Project Alberta, the group responsible for the final bomb assembly. He flew as a scientific observer on a B-29 bomber for the Hiroshima bombing mission, measuring the size of the shock wave to determine the bomb’s power. He also filmed the explosion with a movie camera.

The plutonium core (the box) in the Fat Man weighed 6.2 kg or about 14 lb, the pit is 9 cm (4 inches) across. And only about one fifth of it, a bit over 1 kg (2 pounds) undergoes a fission reaction. And only a gram (1/30th of an ounce) of that gets converted into explosive energy equal to 21,000 tons of TNT.

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