10 gram sample
|half-life||4.468 billion years|
|parent isotopes||242pu (α)|
|isotope mass||238.05078826 u|
|decay mode||decay energy (mev)|
|isotopes of uranium |
complete table of nuclides
uranium-238 (238u or u-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%. unlike uranium-235, it is non-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 transmuted to fissile plutonium-239. 238u cannot support a chain reaction because inelastic scattering reduces neutron energy below the range where fast fission of one or more next-generation nuclei is probable. doppler broadening of 238u's neutron absorption resonances, increasing absorption as fuel temperature increases, is also an essential negative feedback mechanism for reactor control.
around 99.284% of natural uranium's mass is uranium-238, which has a half-life of 1.41×1017 seconds (4.468×109 years, or 4.468 billion years).
due to its natural abundance and half-life relative to other radioactive elements, 238u produces ~40% of the radioactive heat produced within the earth. 238u decay contributes 6 electron anti-neutrinos per decay (1 per beta decay), resulting in a large detectable geoneutrino signal when decays occur within the earth. the decay of 238u to daughter isotopes is extensively used in radiometric dating, particularly for material older than ~ 1 million years.
depleted uranium has an even higher concentration of the 238u isotope, and even low-enriched uranium (leu), while having a higher proportion of the uranium-235 isotope (in comparison to depleted uranium), is still mostly 238u. reprocessed uranium is also mainly 238u, with about as much uranium-235 as natural uranium, a comparable proportion of uranium-236, and much smaller amounts of other isotopes of uranium such as uranium-234, uranium-233, and uranium-232.