Isotopes of calcium

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 radioisotopes are 45Ca with a half-life of 163 days and 47Ca with a half-life of 4.5 days. All other calcium isotopes have half-lives measured in minutes or less.[2]

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.

Main isotopes of calcium (20Ca)
Iso­tope Decay
abun­dance half-life (t1/2) mode pro­duct
40Ca 96.941% stable
41Ca trace 1.03×105 y ε 41K
42Ca 0.647% stable
43Ca 0.135% stable
44Ca 2.086% stable
45Ca syn 162.7 d β 45Sc
46Ca 0.004% stable
47Ca syn 4.5 d β 47Sc
48Ca 0.187% 6.4×1019 y ββ 48Ti
Standard atomic weight Ar, standard(Ca)

List of isotopes

Z(p) N(n)  
isotopic mass (u)
half-life[n 1] decay
mode(s)[3][n 2]
isotope(s)[n 3]
spin and
(mole fraction)
range of natural
(mole fraction)
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 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) (6.4+0.7
)×1019 a
ββ[n 9][n 10] 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
58Ca 20 38 57.997940(540)# 3# ms β 58Sc 0+
β, n 57Sc
  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 ββ 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
  10. ^ Theorized to also undergo β decay to 48Sc with a partial half-life exceeding 1.1+0.8
    ×1021 years[4]


  • 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).


  1. ^ 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.
  2. ^ Audi, G.; Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S. (2017), "The NUBASE2016 evaluation of nuclear properties" (PDF), Chinese Physics C, 41 (3): 030001–1—030001–138, Bibcode:2017ChPhC..41c0001A, doi:10.1088/1674-1137/41/3/030001
  3. ^ "Universal Nuclide Chart". nucleonica. (Registration required (help)).
  4. ^ Aunola, M.; Suhonen, J.; Siiskonen, T. (1999). "Shell-model study of the highly forbidden beta decay 48Ca → 48Sc". EPL. 46 (5): 577. doi:10.1209/epl/i1999-00301-2.

Further reading

External links

42 (number)

42 (forty-two) is the natural number that succeeds 41 and precedes 43.

Alkaline earth metal

The alkaline earth metals are six chemical elements in group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). The elements have very similar properties: they are all shiny, silvery-white, somewhat reactive metals at standard temperature and pressure.Structurally, they have in common an outer s- electron shell which is full;

that is, this orbital contains its full complement of two electrons, which these elements readily lose to form cations with charge +2, and an oxidation state of +2.All the discovered alkaline earth metals occur in nature, although radium occurs only through the decay chain of uranium and thorium and not as a primordial element. Experiments have been conducted to attempt the synthesis of element 120, the next potential member of the group, but they have all met with failure.


Calcium is a chemical element with symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to its heavier homologues strontium and barium. It is the fifth most abundant element in Earth's crust and the third most abundant metal, after iron and aluminium. The most common calcium compound on Earth is calcium carbonate, found in limestone and the fossilised remnants of early sea life; gypsum, anhydrite, fluorite, and apatite are also sources of calcium. The name derives from Latin calx "lime", which was obtained from heating limestone.

Some calcium compounds were known to the ancients, though their chemistry was unknown until the seventeenth century. Pure calcium was isolated in 1808 via electrolysis of its oxide by Humphry Davy, who named the element. Calcium compounds are widely used in many industries: in foods and pharmaceuticals for calcium supplementation, in the paper industry as bleaches, as components in cement and electrical insulators, and in the manufacture of soaps. On the other hand, the metal in pure form has few applications due to its high reactivity; still, in small quantities it is often used as an alloying component in steelmaking, and sometimes, as a calcium–lead alloy, in making automotive batteries.

Calcium is the most abundant metal and the fifth-most abundant element in the human body. As electrolytes, calcium ions play a vital role in the physiological and biochemical processes of organisms and cells: in signal transduction pathways where they act as a second messenger; in neurotransmitter release from neurons; in contraction of all muscle cell types; as cofactors in many enzymes; and in fertilization. Calcium ions outside cells are important for maintaining the potential difference across excitable cell membranes as well as proper bone formation.


Calcium-48 is a scarce isotope of calcium containing 20 protons and 28 neutrons. It makes up 0.187% of natural calcium by mole fraction. Although it is unusually neutron-rich for such a light nucleus, its beta decay is extremely hindered, and so the only radioactive decay pathway that it has been observed to undergo is the extremely rare process of double beta decay. Its half-life is about 6.4×1019 years, so for all practical purposes it can be treated as stable. One factor contributing to this unusual stability is that 20 and 28 are both magic numbers, making 48Ca a "doubly magic" nucleus.

Since 48Ca is both practically stable and neutron-rich, it is a valuable starting material for the production of new nuclei in particle accelerators, both by fragmentation and by fusion reactions with other nuclei, for example in the discoveries of the heaviest five elements on the periodic table, from flerovium to oganesson. Heavier nuclei generally require a greater fraction of neutrons for maximum stability, so neutron-rich starting materials are necessary.

48Ca is the lightest nucleus known to undergo double beta decay and the only one simple enough to be analyzed with the sd nuclear shell model. It also releases more energy (4.27 MeV) than any other double beta decay candidate. These properties make it an interesting probe of nuclear structure models and a promising candidate in the ongoing search for neutrinoless double beta decay.

Calcium (disambiguation)

Calcium is a chemical element with symbol Ca and atomic number 20.

Calcium may also refer to:

Calcium, New York, a census-designated place in Jefferson County, New York

Calcium, Queensland, a locality in the City of Townsville, Australia

"Calcium", a song on the album Accelerator by The Future Sound of London

"Calcium", a song on the album DeadBoy by Bones

Donald J. DePaolo

Donald J. DePaolo is an American professor of geochemistry in the Department of Earth and Planetary Science at the University of California, Berkeley and Associate Laboratory Director for Energy and Environmental Sciences at the Lawrence Berkeley National Laboratory.

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.