- Isotopes of rubidium
Rubidium (Rb) has 24isotope s, with naturally occurring rubidium being composed of just two isotopes; Rb-85 (72.2%) and theradioactive Rb-87 (27.8%). Normal mixes of rubidium are radioactive enough to fogphotographic film in approximately 30 to 60 days. Standard atomic mass is 85.4678(3) uRb-87 has a
half-life of 4.88×1010 years. It readily substitutes forpotassium inmineral s, and is therefore fairly widespread. Rb has been used extensively in dating rocks; Rb-87 decays to stablestrontium -87 by emission of a negativebeta particle . During fractional crystallization, Sr tends to become concentrated inplagioclase , leaving Rb in the liquid phase. Hence, the Rb/Sr ratio in residualmagma may increase over time, resulting in rocks with increasing Rb/Sr ratios with increasing differentiation. Highest ratios (10 or higher) occur inpegmatite s. If the initial amount of Sr is known or can be extrapolated, the age can be determined by measurement of the Rb and Sr concentrations and the Sr-87/Sr-86 ratio. The dates indicate the true age of the minerals only if the rocks have not been subsequently altered. Seerubidium-strontium dating for a more detailed discussion.Rb-82 is used in some
cardiac PET scans to assess myocardial perfusion. It has ahalf-life of 1.273 minutes. It does not exist naturally, but can be made from the decay of Sr-82.Table
Notes
* 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.
* 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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