Thin Man (nuclear bomb)

Thin Man
"Thin Man" plutonium gun test casings
Type	Nuclear weapon
Place of origin	United States
Production history
Designer	Los Alamos Laboratory
Specifications
Length	17 feet (5.2 m)
Diameter	38 inches (97 cm)
Filling	Plutonium

"Thin Man" was the codename for a proposed plutonium gun-type nuclear bomb using plutonium-239 which the United States was developing during the Manhattan Project. Its development was aborted when it was discovered that the spontaneous fission rate of their nuclear-reactor-bred plutonium was too high for use in a gun-type design, due to the too high concentration of the isotope plutonium-240.

In 1942, prior to the Army taking over wartime atomic research, Robert Oppenheimer held conferences in Chicago in June and Berkeley, California, in July at which various engineers and physicists discussed nuclear bomb design issues. A gun-type design was chosen, in which two sub-critical masses would be brought together by firing a "bullet" into a "target". The idea of an implosion-type nuclear weapon was suggested by Richard Tolman but attracted scant consideration.

Oppenheimer, reviewing his options in early 1943, gave priority to the gun-type weapon, but as a hedge against the threat of pre-detonation, he created the E-5 Group at the Los Alamos Laboratory under Seth Neddermeyer to investigate implosion. Implosion-type bombs were determined to be significantly more efficient in terms of explosive yield per unit mass of fissile material in the bomb, because compressed fissile materials react more rapidly and therefore more completely. It was decided that the plutonium gun would receive the bulk of the research effort, since it was the project with the least amount of uncertainty involved. It was assumed that the uranium gun-type bomb could be more easily adapted from it.