Isotopes of uranium


Isotopes of uranium

Uranium (U) is a naturally occurring element with no stable isotopes. In other words, all uranium is radioactive and hence vanishing by radioactive decay, yet it is also found in great quantity in the earth's crust. The natural isotopes are uranium-234, uranium-235, and uranium-238, with the average atomic mass in nature being 238.02891(3) u. In addition, other useful isotopes such as uranium-232 have been produced in mass quantity in breeder reactors.

Historically, isotopes of uranium were known as
* "uranium II", 234U
* "actino-uranium", 235U
* "uranium I", 238U

Naturally occurring uranium is composed of three major isotopes, uranium-238 (99.28% natural abundance), uranium-235 (0.71%), and uranium-234 (0.0054%). All three isotopes are radioactive, creating radioisotopes, with the most abundant and stable being uranium-238 with a half-life of 4.51e|9 years (close to the age of the Earth), uranium-235 with a half-life of 7.13e|8 years, and uranium-234 with a half-life of 2.48e|5 years.Seaborg, "Encyclopedia of the Chemical Elements" (1968), page 777]

Uranium-238 is an α emitter, decaying through the 18-member uranium natural decay series into lead-206. The decay series of uranium-235 (also called actino-uranium) has 15 members that ends in lead-207, protactinium-231 and actinium-227.] 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.

The isotope uranium-235 is important for both nuclear reactors and nuclear weapons because it is the only isotope existing in nature to any appreciable extent that is fissile, that is, can be broken apart by thermal neutrons. The isotope uranium-238 is also important because it absorbs neutrons to produce a radioactive isotope that subsequently decays to the isotope plutonium-239, which also is fissile.

Table

Notes

* Evaluated isotopic composition is for most but not all commercial samples.
* The precision of the isotope abundances and atomic mass is limited through variations. The given ranges should be applicable to any normal terrestrial material.
* Geologically exceptional samples are known in which the isotopic composition lies outside the reported range. The uncertainty in the atomic mass may exceed the stated value for such specimens.
* Commercially available materials may have been subjected to an undisclosed or inadvertent isotopic fractionation. Substantial deviations from the given mass and composition can occur.
* Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
* Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.

References

* Isotope masses from [http://www.nndc.bnl.gov/amdc/index.html Ame2003 Atomic Mass Evaluation] by G. Audi, A.H. Wapstra, C. Thibault, J. Blachot and O. Bersillon in "Nuclear Physics" A729 (2003).
* Isotopic compositions and standard atomic masses from [http://www.iupac.org/publications/pac/2003/7506/7506x0683.html Atomic weights of the elements. Review 2000 (IUPAC Technical Report)] . "Pure Appl. Chem." Vol. 75, No. 6, pp. 683-800, (2003) and [http://www.iupac.org/news/archives/2005/atomic-weights_revised05.html Atomic Weights Revised (2005)] .
* Half-life, spin, and isomer data selected from these sources. Editing notes on this article's talk page.
** Audi, Bersillon, Blachot, Wapstra. [http://amdc.in2p3.fr/web/nubase_en.html The Nubase2003 evaluation of nuclear and decay properties] , Nuc. Phys. A 729, pp. 3-128 (2003).
** National Nuclear Data Center, Brookhaven National Laboratory. Information extracted from the [http://www.nndc.bnl.gov/nudat2/ NuDat 2.1 database] (retrieved Sept. 2005).
** David R. Lide (ed.), Norman E. Holden in "CRC Handbook of Chemistry and Physics, 85th Edition", online version. CRC Press. Boca Raton, Florida (2005). Section 11, Table of the Isotopes.


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