![]() ![]() , as in weapons-grade plutonium (less than 7% 240Pu) is achieved by reprocessing the fuel after just 90 days of use. Even with this design, it was estimated in advance of the Trinity test that 240Pu impurity would cause a 12% chance of the explosion failing to reach its maximum yield. It blocked the use of plutonium in gun-type nuclear weapons in which the assembly of fissile material into its optimal supercritical mass configuration can take up to a millisecond to complete, and made it necessary to develop implosion-style weapons where the assembly occurs in a few microseconds. The spontaneous fission problem was extensively studied by the scientists of the Manhattan Project during World War II. Isotopes besides 239Pu produce more decay heat, which can cause phase change distortions of the precision core if allowed to build up.Isotopes besides 239Pu release significantly more radiation, which complicates its handling by workers.The presence of 240Pu would thus randomly cause fizzles, with an explosive yield well below the potential yield. A single stray neutron that is introduced while the core is supercritical will cause it to detonate almost immediately, even before it has been crushed to an optimal configuration. 240Pu has a high rate of spontaneous fission.The inevitable presence of some 240Pu in a plutonium-based nuclear warhead core complicates its design, and pure 239Pu is considered optimal. Thus, even mass isotopes tend to accumulate, especially in a thermal reactor. In general, isotopes of odd mass numbers are more likely to absorb a neutron, and can undergo fission upon neutron absorption more easily than isotopes of even mass number. When the isotope 240Pu captures a neutron, it is about 4500 times more likely to become plutonium-241 than to fission. 269.3 ☒.9 barns), but only a tiny thermal neutron fission cross section (0.064 barns). The isotope 240Pu has about the same thermal neutron capture cross section as 239Pu ( 289.5 ☑.4 vs. The longer a nuclear fuel element remains in a nuclear reactor, the greater the relative percentage of 240Pu in the fuel becomes. It decays by alpha emission to uranium-236.Ībout 62% to 73% of the time when 239Pu captures a neutron, it undergoes fission the remainder of the time, it forms 240Pu. ![]() The presence of 240Pu limits plutonium's use in a nuclear bomb, because the neutron flux from spontaneous fission initiates the chain reaction prematurely, causing an early release of energy that physically disperses the core before full implosion is reached. Ģ40Pu undergoes spontaneous fission as a secondary decay mode at a small but significant rate. The detection of its spontaneous fission led to its discovery in 1944 at Los Alamos and had important consequences for the Manhattan Project. Or Pu-240) is an isotope of plutonium formed when plutonium-239 captures a neutron. Isotope of plutonium Plutonium-240, 240Pu General ![]()
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