My career 238


August 20, 2022

Uranium 238 (238U or U-238) is the most common isotope of uranium found in nature, accounting for about 99.284% of the mass of uranium. There are two parent isotopes of uranium 238, 242Pu and 238Pa. The parent isotope 242Pu, when α decays, produces a daughter isotope 238U. And the parent isotope 238Pa when decaying β- also produces 238U. Uranium 238 has 146 neutrons and 92 protons. Its isotope mass is 238.05078826 u. Unlike uranium-235, it is not fissile, which means it cannot sustain a chain reaction in a thermal neutron reactor. However, it is fissionable by fast neutrons, and is fertile, meaning it can be converted to fissile plutonium-239.238 U cannot support a chain reaction because of inelastic scattering. Recovery reduces neutron energy below the range where rapid fission of one or more next-generation nuclei can occur. Doppler expansion of U-238's neutron absorption resonance, which increases absorption as fuel temperature increases, is also an essential negative feedback mechanism for reactor control. Approximately 99.286% of the mass of natural uranium is uranium-238, which has a half-life of 1.41 × 10 17 seconds (4.468 × 10 9 years, or 4.468 billion years). Due to its natural abundance and half-life compared to other radioactive elements, 238 U produces ~40% of the radioactive heat generated in the Earth. The 238U decay contributes 6 antineutrino electrons per decay (1 beta decay), resulting in a large geoneutrino signal that can be detected as decay occurs within the Earth. >The decay of 238 U isotopes to near isotopes is widely used in radiometric dating, especially for material older than ~1 million years. Depleted uranium has a higher concentration of the 238 U isotope, and even depleted uranium (LEU), while having a higher proportion of the uranium-235 isotope (compared to depleted uranium), is still mostly 238 U. Recycled uranium is also mainly 238 U, with uranium-235 equivalents to natural uranium, in proportions comparable to uranium-236 and small amounts of other uranium isotopes such as uranium-234, uranium-233 and uranium-233. uranium-232.


Although heavier than 235U, the half-life of 238U (4.468 billion years) is larger than the half-life of 235U (760 million years). When fission, uranium 238 gives off an energy equal to 4,267 MeV. It can only fission with fast neutron absorption and alpha decay, but it can capture a slow neutron and after 2 beta decays it becomes fissile 239Pu. Uranium 238 will fission upon absorbing fast neutrons, it will fission but cannot support a chain reaction because inelastic scattering reduces the residual neutron energy below what fast fission would require. happen.


The main application of 238U is as a feedstock for the production of 239Pu and as a fission fuel. It is also used to make 3F bombs, make uranium glass, polish dyes, etc.

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