Isotopes of calcium
|Standard atomic weight (Ar, standard)|
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Calcium (20Ca) has 27 isotopes, from 34Ca to 60Ca. There are five stable isotopes (40Ca, 42Ca, 43Ca, 44Ca and 46Ca), plus one isotope (48Ca) with such a long half-life that for all practical purposes it can be considered stable. The most abundant isotope, 40Ca, as well as the rare 46Ca, are theoretically unstable on energetic grounds, but their decay has not been observed. Calcium also has a cosmogenic isotope, radioactive 41Ca, which has a half-life of 102,000 years. Unlike cosmogenic isotopes that are produced in the atmosphere, 41Ca is produced by neutron activation of 40Ca. Most of its production is in the upper metre or so of the soil column, where the cosmogenic neutron flux is still sufficiently strong. 41Ca has received much attention in stellar studies because it decays to 41K, a critical indicator of solar-system anomalies. The most stable artificial radioisotope is 45Ca, with a half-life of 163 days.
All other calcium isotopes have half-lives of 163 days or less, most under a minute. The least stable is 34Ca with a half-life shorter than 35 nanoseconds.
40Ca comprises about 97% of naturally occurring calcium. 40Ca is also one of the daughter products of 40K decay, along with 40Ar. While K-Ar dating has been used extensively in the geological sciences, the prevalence of 40Ca in nature has impeded its use in dating. Techniques using mass spectrometry and a double spike isotope dilution have been used for K–Ca age dating.
List of isotopes
This article needs to be updated.(July 2018)
isotopic mass (u)
|range of natural|
|35Ca||20||15||35.00494(21)#||25.7(2) ms||β+ (>99.9%)||35K||1/2+#|
|β+, p (<.1%)||34Ar|
|36Ca||20||16||35.99309(4)||102(2) ms||β+, p (56.8%)||35Ar||0+|
|37Ca||20||17||36.985870(24)||181.1(10) ms||β+, p (74.5%)||36Ar||(3/2+)|
|40Ca[n 4]||20||20||39.96259098(22)||Observationally Stable[n 5]||0+||0.96941(156)||0.96933–0.96947|
|41Ca||20||21||40.96227806(26)||1.02(7)×105 y||EC||41K||7/2−||Trace[n 6]|
|46Ca||20||26||45.9536926(24)||Observationally Stable[n 7]||0+||4(3)×10−5||4×10−5–4×10−5|
|51Ca||20||31||50.9615(1)||10.0(8) s||β− (>99.9%)||51Sc||(3/2−)#|
|β−, n (<.1%)||50Sc|
|52Ca||20||32||51.96510(75)||4.6(3) s||β− (98%)||52Sc||0+|
|β−, n (2%)||51Sc|
|53Ca||20||33||52.97005(54)#||90(15) ms||β− (70%)||53Sc||3/2−#|
|β−, n (30%)||52Sc|
|54Ca||20||34||53.97435(75)#||50# ms [>300 ns]||β−, n||53Sc||0+|
|55Ca||20||35||54.98055(75)#||30# ms [>300 ns]||β−||55Sc||5/2−#|
|56Ca||20||36||55.98557(97)#||10# ms [>300 ns]||β−||56Sc||0+|
- Bold for isotopes with half-lives longer than the age of the universe (nearly stable)
EC: Electron capture
- Bold for stable isotopes
- Heaviest nuclide with equal numbers of protons and neutrons with no observed decay
- Believed to undergo double electron capture to 40Ar with a half-life no less than 5.9×1021 a
- Cosmogenic nuclide
- Believed to undergo β−β− decay to 46Ti with a half-life no less than 2.8×1015 a
- Primordial radionuclide
- Lightest nuclide known to undergo double beta decay
- 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.
- 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.
- Nuclide masses are given by IUPAP Commission on Symbols, Units, Nomenclature, Atomic Masses and Fundamental Constants (SUNAMCO).
- Isotope abundances are given by IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW).
- Meija, J.; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265–91. doi:10.1515/pac-2015-0305.
- "Universal Nuclide Chart". nucleonica. (Registration required (help)).
- Isotope masses from:
- Isotopic compositions and standard atomic masses from:
- J. R. de Laeter; J. K. Böhlke; P. De Bièvre; H. Hidaka; H. S. Peiser; K. J. R. Rosman; P. D. P. Taylor (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry. 75 (6): 683–800. doi:10.1351/pac200375060683.
- M. E. Wieser (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry. 78 (11): 2051–2066. doi:10.1351/pac200678112051. Lay summary.
- Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
- G. Audi; A. H. Wapstra; C. Thibault; J. Blachot; O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001. Archived from the original (PDF) on 2008-09-23.
- National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. Retrieved 23 February 2017.
- N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide. CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0-8493-0485-9.
- C. Michael Hogan. 2010. Calcium. ed. A. Jorgenson and C. Cleveland. Encyclopedia of Earth, National Council for Science and the Environment, Washington, D.C.