Fat Man

Fat Man

The Fat Man bomb being readied. Note the tail fin is signed.

The rapid spontaneous fission rate of plutonium 239 necessitated that a different type of bomb be designed. A gun-type bomb would not be fast enough to work. Before the bomb could be assembled, a few stray neutrons would have been emitted, and these would start a premature chain reaction­leading to a great reduction in the energy released.

Seth Neddermeyer, a scientist at Los Alamos, developed the idea of using explosive charges to compress a sphere of plutonium very rapidly to a density sufficient to make it go critical and produce a nuclear explosion.

Fat Man Specifications

Length: 128.375 inches (10 feet 8 inches / 3.25 meters)
Diameter: 60.25 inches (5 feet / 1.5 meters)
Weight: 10,265 lbs (4,656 kg)
Yield: 21 kilotons (+/- 10%)