Isotopes of argon

The main isotopes of argon (Ar) found on Earth are ⁴⁰Ar, ³⁶Ar, and ³⁸Ar. Naturally occurring ⁴⁰K with a half-life of 1.250e|9 years, decays to stable ⁴⁰Ar (11.2%) by electron capture and by positron emission, and also transforms to stable ⁴⁰Ca (88.8%) via beta decay. These properties and ratios are used to determine the age of rocks through potassium-argon dating.cite web |url=http://www.geoberg.de/text/geology/07011601.php |title=⁴⁰Ar/³⁹Ar dating and errors |accessdate=2007-03-07]

In the Earth's atmosphere, ³⁹Ar is made by cosmic ray activity, primarily with ⁴⁰Ar. In the subsurface environment, it is also produced through neutron capture by ³⁹K or alpha emission by calcium. The content of ³⁹Ar in natural argon is measured to be of (8.0±0.6)×10⁻¹⁶ g/g, or (1.01±0.08) Bq/kg of ^natAr [P. Benetti et al., Measurement of the specific activity of ³⁹Ar in natural argon. Nucl. Instr. Meth. A 574 (2007) 83 [http://dx.doi.org/10.1016/j.nima.2007.01.106] .] . ³⁷Ar is created from the decay of ⁴⁰Ca as a result of subsurface nuclear explosions. It has a half-life of 35 days. The content of ⁴²Ar in the Earth's atmosphere is lower than 6×10⁻²¹ parts per part of ^natAr [V. D. Ashitkov et al., New experimental limit on the ⁴²Ar content in the Earth’s atmosphere. Nucl. Instr. Meth. A 416 (1998) 179 [http://dx.doi.org/10.1016/S0168-9002(98)00740-2] .] .

Standard atomic mass: 39.948(1) u.

Table

Notes

* The isotopic composition refers to that in air.
* 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.

External links

* [http://ie.lbl.gov/education/parent/Ar_iso.htm Argon isotopes data from "The Berkeley Laboratory Isotopes Project's"]