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Isotopes of calcium

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Calcium (Ca) has a total of 24 isotopes, from 34Ca to 57Ca. 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 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.
Standard atomic mass: 40.078(4) u

Table

nuclide
symbol 		Z(p) N(n)  
isotopic mass (u)
  		half-life[n 1] decay
mode(s)[1][n 2] 		daughter
isotope(s)[n 3] 		nuclear
spin 		representative
isotopic
composition
(mole fraction) 		range of natural
variation
(mole fraction)
34Ca 20 14 34.01412(32)# <35 ns p 33K 0+
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+
β+ (43.2%) 36K
37Ca 20 17 36.985870(24) 181.1(10) ms β+, p (74.5%) 36Ar (3/2+)
β+ (25.5%) 37K
38Ca 20 18 37.976318(5) 440(8) ms β+ 38K 0+
39Ca 20 19 38.9707197(20) 859.6(14) ms β+ 39K 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 a EC 41K 7/2- Trace[n 6]
42Ca 20 22 41.95861801(27) Stable 0+ 0.00647(23) 0.00646-0.00648
43Ca 20 23 42.9587666(3) Stable 7/2- 0.00135(10) 0.00135-0.00135
44Ca 20 24 43.9554818(4) Stable 0+ 0.02086(110) 0.02082-0.02092
45Ca 20 25 44.9561866(4) 162.67(25) d β- 45Sc 7/2-
46Ca 20 26 45.9536926(24) Observationally Stable[n 7] 0+ 4(3)×10−5 4×10−5-4×10−5
47Ca 20 27 46.9545460(24) 4.536(3) d β- 47Sc 7/2-
48Ca[n 8] 20 28 47.952534(4) 43(38)×1018 a β-β-[n 9] 48Ti 0+ 0.00187(21) 0.00186-0.00188
49Ca 20 29 48.955674(4) 8.718(6) min β- 49Sc 3/2-
50Ca 20 30 49.957519(10) 13.9(6) s β- 50Sc 0+
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+
β- 54Sc
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+
57Ca 20 37 56.99236(107)# 5# ms β- 57Sc 5/2-#
β-, n 56Sc
  1. ^ Bold for isotopes with half-lives longer than the age of the universe (nearly stable)
  2. ^ Abbreviations:
    EC: Electron capture
  3. ^ Bold for stable isotopes
  4. ^ Heaviest nuclide with equal numbers of protons and neutrons with no observed decay
  5. ^ Believed to undergo double electron capture to 40Ar with a half-life no less than 5.9×1021 a
  6. ^ Cosmogenic nuclide
  7. ^ Believed to undergo β-β- decay to 46Ti with a half-life no less than 2.8×1015 a
  8. ^ Primordial radionuclide
  9. ^ Lightest nuclide known to undergo double beta decay

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.
  • 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.

References

  1. ^ http://www.nucleonica.net/unc.aspx
  • Isotope masses from:
    • G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and 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.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  • Isotopic compositions and standard atomic masses from:
  • Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.

Further reading

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