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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.
Decay chain of 240 Pu. Plutonium-240 (240 Pu or Pu-240) is an isotope of plutonium formed when plutonium-239 captures a neutron.The detection of its spontaneous fission led to its discovery in 1944 at Los Alamos and had important consequences for the Manhattan Project.
Weapons-grade plutonium is defined as being predominantly Pu-239, typically about 93% Pu-239. [24] Pu-240 is produced when Pu-239 absorbs an additional neutron and fails to fission. Pu-240 and Pu-239 are not separated by reprocessing. Pu-240 has a high rate of spontaneous fission, which can cause a
240 Pu undergoes spontaneous fission at a small but significant rate (5.8 × 10 −6 %). [1] The presence of 240 Pu limits the plutonium's use in a nuclear bomb, because a neutron from spontaneous fission starts the chain reaction prematurely, causing an early release of energy that disperses the core before full implosion is reached. This ...
Nov. 1—Production of plutonium pits at the Savannah River Site and Los Alamos National Laboratory remains a top priority of the U.S. Department of Defense and the National Nuclear Security ...
Feb. 19—Los Alamos National Laboratory reached what federal officials say is a key milestone in developing its first plutonium pit that can be placed in a nuclear warhead as it seeks to produce ...
A big reason the lab is working toward producing 30 fresh plutonium cores is some federal scientists and nuclear security officials contend the Cold War pits have grown too old to be reliable ...
Trace amounts of plutonium-238, plutonium-239, plutonium-240, and plutonium-244 can be found in nature. Small traces of plutonium-239, a few parts per trillion , and its decay products are naturally found in some concentrated ores of uranium, [ 54 ] such as the natural nuclear fission reactor in Oklo , Gabon . [ 55 ]