Thin Man (nuclear bomb) Thin Man (nuclear bomb) "Thin Man" was the code name for a proposed plutonium gun-type nuclear bomb using plutonium-239 which the United States was developing during the Manhattan Project. They aborted its development when they 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 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
Soviet atomic bomb project theory, alongside Isaak Pomeranchuk. Despite early and accelerated efforts, it was reported by historians that efforts on building a bomb using weapon-grade uranium seemed hopeless to Russian scientists. Igor Kurchatov had harboured doubts working towards the uranium bomb, made progress on a bomb using weapon-grade plutonium after British data was provided by the NKVD. The situation dramatically changed when the Soviet Union learned of the atomic bombings of Hiroshima and Nagasaki in 1945, which eventually led to the unilateral surrender of Japan to the United States, ending the war in Asia. Immediately after the atomic bombing, the Soviet Politburo took