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The name Fat Man refers to the early design of the bomb because it had a wide, round shape. Fat Man was an implosion-type nuclear weapon with a solid plutonium core. The first of that type to be detonated was the Gadget in the Trinity nuclear test less than a month earlier on 16 July at the Alamogordo Bombing and Gunnery Range in New Mexico.
The Fat Man device specifically used 6.2 kg (14 lb), about 350 ml or 12 US fl oz in volume, of Pu-239, which is only 41% of bare-sphere critical mass (see Fat Man article for a detailed drawing). Surrounded by a U-238 reflector/tamper, the Fat Man's pit was brought close to critical mass by the neutron-reflecting properties of the U-238. During ...
The nuclear arms race was an arms race competition for ... was more or less a copy of "Fat Man", ... "The Cold War and the Nuclear Arms Race", and "Nuclear Weapons ...
Fat Man was the second nuclear weapon to be deployed in combat after the US dropped a 5-ton atomic bomb, called "Little Boy," on the Japanese city of Hiroshima.
The Mark 4 nuclear bomb was an American implosion-type nuclear bomb based on the earlier Mark 3 Fat Man design, used in the Trinity test and the bombing of Nagasaki.With the Mark 3 needing each individual component to be hand-assembled by only highly trained technicians under closely controlled conditions, the purpose of the Mark 4 was to produce an atomic weapon as a practical piece of ordnance.
Mark 3 – "Fat Man" plutonium implosion weapon (used against Nagasaki), effectively the same as the "Gadget" device used in the Trinity nuclear test with minor design differences. (21 kilotons, 1945–1950) Mark 4 – Post-war "Fat Man" redesign. Bomb designed with weapon characteristics as the foremost criteria. (1949–1953)
The pits of the first nuclear weapons were solid, with an urchin neutron initiator in their center. The Gadget and Fat Man used pits made of 6.2 kg of solid hot pressed plutonium-gallium alloy (at 400 °C and 200 MPa in steel dies – 750 °F and 29,000 psi) half-spheres of 9.2 cm (3.6 in) diameter, with a 2.5 cm (1 in) internal cavity for the initiator.
The Trinity bomb was officially a Y-1561 device, as was the Fat Man used later in the bombing of Nagasaki. The two were very similar, though the Trinity bomb lacked fuzing and external ballistic casing. The bombs were still under development, and small changes continued to be made to the Fat Man design. [59]