Isotopes of calcium

Calcium (Ca) has 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.
Relative atomic mass: 40.078(4)

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)×10^5 y	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)×10^18 y	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. "Universal Nuclide Chart". nucleonica. (registration required (help)).

• Isotope masses from:
  • 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.
• 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.
  • National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. Retrieved September 2005.
  • 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.

Further reading

• C. Michael Hogan. 2010. Calcium. ed. A. Jorgenson and C. Cleveland. Encyclopedia of Earth, National Council for Science and the Environment, Washington, D.C.

External links

• Calcium isotopes data from The Berkeley Laboratory Isotopes Project's