Nuclides with atomic number of 92 but with different mass numbers
Isotopes of uranium (92U)
Main isotopes[1]
Decay
abundance
half-life (t1/2)
mode
product
232U
synth
68.9 y
α
228Th
SF
–
233U
trace
1.592×105 y[2]
α
229Th
SF
–
234U
0.005%
2.455×105 y
α
230Th
SF
–
235U
0.720%
7.04×108 y
α
231Th
SF
–
236U
trace
2.342×107 y
α
232Th
SF
–
238U
99.3%
4.468×109 y
α
234Th
SF
–
β−β−
238Pu
Standard atomic weight Ar°(U)
238.02891±0.00003[3]
238.03±0.01 (abridged)[4]
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Uranium (92U) is a naturally occurring radioactive element that has no stable isotope. It has two primordial isotopes, uranium-238 and uranium-235, that have long half-lives and are found in appreciable quantity in the Earth's crust. The decay product uranium-234 is also found. Other isotopes such as uranium-233 have been produced in breeder reactors. In addition to isotopes found in nature or nuclear reactors, many isotopes with far shorter half-lives have been produced, ranging from 214U to 242U (with the exception of 220U). The standard atomic weight of natural uranium is 238.02891(3).
Natural uranium consists of three main isotopes, 238U (99.2739–99.2752% natural abundance), 235U (0.7198–0.7202%), and 234U (0.0050–0.0059%).[5] All three isotopes are radioactive (i.e., they are radioisotopes), and the most abundant and stable is uranium-238, with a half-life of 4.4683×109 years (about the age of the Earth).
Uranium-238 is an alpha emitter, decaying through the 18-member uranium series into lead-206. The decay series of uranium-235 (historically called actino-uranium) has 15 members and ends in lead-207. The constant rates of decay in these series makes comparison of the ratios of parent-to-daughter elements useful in radiometric dating. Uranium-233 is made from thorium-232 by neutron bombardment.
Uranium-235 is important for both nuclear reactors (energy production) and nuclear weapons because it is the only isotope existing in nature to any appreciable extent that is fissile in response to thermal neutrons, i.e., thermal neutron capture has a high probability of inducing fission. A chain reaction can be sustained with a sufficiently large (critical) mass of uranium-235. Uranium-238 is also important because it is fertile: it absorbs neutrons to produce a radioactive isotope that subsequently decays to the isotope plutonium-239, which also is fissile.
^Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
^Magurno, B.A.; Pearlstein, S, eds. (1981). Proceedings of the conference on nuclear data evaluation methods and procedures. BNL-NCS 51363, vol. II(PDF). Upton, NY (USA): Brookhaven National Lab. pp. 835 ff. Retrieved 2014-08-06.
^"Standard Atomic Weights: Uranium". CIAAW. 1999.
^Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
^"Uranium Isotopes". GlobalSecurity.org. Retrieved 14 March 2012.
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