Preparing the Little Boy Bomb

roject A (Alberta) member CDR A. Francis Birch (left) numbers Little Boy Unit L-11 while Norman Ramsey (right) watches.
Project A (Alberta) member CDR A. Francis Birch (left) numbers Little Boy Unit L-11 while Norman Ramsey (right) watches.

In essence, the Little Boy design consisted of a gun that fired one mass of uranium 235 at another mass of uranium 235, thus creating a supercritical mass. A crucial requirement was that the pieces be brought together in a time shorter than the time between spontaneous fissions. Once the two pieces of uranium are brought together, the initiator introduces a burst of neutrons and the chain reaction begins, continuing until the energy released becomes so great that the bomb simply blows itself apart.

Little Boy Specifications

Length: 120.0 inches (10 feet / 3.0 meters)
Diameter: 28.0 inches (71.1 cm)
Weight: 9,700 lbs (4,400 kg)
Yield: 15 kiltons (+/- 20%)

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