Isotopes of calcium

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Calcium (20Ca) has 26 known isotopes, ranging from 35Ca to 60Ca. There are five stable isotopes (40Ca, 42Ca, 43Ca, 44Ca and 46Ca), plus one isotope (48Ca) with such a long half-life that it is for all practical purposes 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, 41Ca, with half-life 99,400 years. Unlike cosmogenic isotopes produced in the air, 41Ca is produced by neutron activation of solid 40Ca in rock and soil. Most of its production is in the upper metre of the soil column, where the cosmogenic neutron flux is still strong enough. The most stable artificial isotopes are 45Ca with half-life 162.61 days and 47Ca with half-life 4.536 days. All other calcium isotopes have half-lives of minutes or less.

Quick facts Main isotopes, Decay ...
Isotopes of calcium (20Ca)
Main isotopes[1] Decay
Isotope abun­dance half-life (t1/2) mode pro­duct
40Ca 96.9% stable
41Ca trace 9.94×104 y ε 41K
42Ca 0.647% stable
43Ca 0.135% stable
44Ca 2.09% stable
45Ca synth 162.61 d β− 45Sc
46Ca 0.004% stable
47Ca synth 4.536 d β− 47Sc
48Ca 0.187% 5.6×1019 y β−β− 48Ti
Standard atomic weight Ar°(Ca)
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40Ca comprises about 97% of natural calcium and is mainly created by nucleosynthesis in stars (alpha process). Like 40Ar, however, some 40Ca is radiogenic, created by radioactive decay of 40K. While K–Ar dating has been used extensively in the geological sciences, the prevalence of 40Ca in nature initially impeded the proliferation of K-Ca dating in early studies, with only a handful of studies in the 20th century. Modern techniques using increasingly precise Thermal-Ionization (TIMS) and Collision-Cell Multi-Collector Inductively-coupled plasma mass spectrometry (CC-MC-ICP-MS) techniques, however, have been used for successful K–Ca dating[4][5] similar in method to Rb-Sr dating, as well as determining K losses from the lower continental crust[6] and for source-tracing calcium contributions from various geologic reservoirs.[7][8]

Stable isotope variations of calcium (most typically 44Ca/40Ca or 44Ca/42Ca, denoted 'δ44Ca' and 'δ44/42Ca' in delta notation) are also widely used across the natural sciences for a number of applications, ranging from early determination of osteoporosis[9] to quantifying volcanic eruption timescales.[10] Other applications include: quantifying carbon sequestration efficiency in CO2 injection sites[11] and understanding ocean acidification,[12] exploring both ubiquitous and rare magmatic processes, such as formation of granites[13] and carbonatites,[14] tracing modern and ancient trophic webs including in dinosaurs,[15][16][17] assessing weaning practices in ancient humans,[18] and a plethora of other emerging applications.

List of isotopes


More information Nuclide, Z ...
Nuclide
 Z N Isotopic mass (Da)[19]
[n 1]		 Discovery
year[20]		 Half-life[1]
[n 2]		 Decay
mode[1]
[n 3]		 Daughter
isotope
[n 4]		 Spin and
parity[1]
[n 5][n 6]		 Natural abundance (mole fraction)
Normal proportion[1] Range of variation
35Ca 20 15 35.00557(22)# 1985 25.7(2) ms β+, p (95.8%) 34Ar 1/2+#
β+, 2p (4.2%) 33Cl
β+ (rare) 35K
36Ca 20 16 35.993074(43) 1977 100.9(13) ms β+, p (51.2%) 35Ar 0+
β+ (48.8%) 36K
37Ca 20 17 36.98589785(68) 1964 181.0(9) ms β+, p (76.8%) 36Ar 3/2+
β+ (23.2%) 37K
38Ca 20 18 37.97631922(21) 1966 443.70(25) ms β+ 38K 0+
39Ca 20 19 38.97071081(64) 1943 860.3(8) ms β+ 39K 3/2+
40Ca[n 7] 20 20 39.962590850(22) 1922 Observationally stable[n 8] 0+ 0.9694(16) 0.96933–0.96947
41Ca 20 21 40.96227791(15) 1939 9.94(15)×104 y EC 41K 7/2− Trace[n 9]
42Ca 20 22 41.95861778(16) 1934 Stable 0+ 0.00647(23) 0.00646–0.00648
43Ca 20 23 42.95876638(24) 1934 Stable 7/2− 0.00135(10) 0.00135–0.00135
44Ca 20 24 43.95548149(35) 1922 Stable 0+ 0.0209(11) 0.02082–0.02092
45Ca 20 25 44.95618627(39) 1940 162.61(9) d β− 45Sc 7/2−
46Ca 20 26 45.9536877(24) 1938 Observationally stable[n 10] 0+ 4×10−5 4×10−5–4×10−5
47Ca 20 27 46.9545411(24) 1951 4.536(3) d β− 47Sc 7/2−
48Ca[n 11][n 12] 20 28 47.952522654(18) 1938 5.6(10)×1019 y β−β−[n 13][n 14] 48Ti 0+ 0.00187(21) 0.00186–0.00188
49Ca 20 29 48.95566263(19) 1950 8.718(6) min β− 49Sc 3/2−
50Ca 20 30 49.9574992(17) 1964 13.45(5) s β− 50Sc 0+
51Ca 20 31 50.96099566(56) 1980 10.0(8) s β− 51Sc 3/2−
52Ca 20 32 51.96321365(72) 1985 4.6(3) s β− (>98%) 52Sc 0+
β−, n (<2%) 51Sc
53Ca 20 33 52.968451(47) 1983 461(90) ms β− (60%) 53Sc 1/2−#
β−, n (40%) 52Sc
54Ca 20 34 53.972989(52) 1997 90(6) ms β− 54Sc 0+
55Ca 20 35 54.97998(17) 1997 22(2) ms β− 55Sc 5/2−#
56Ca 20 36 55.98550(27) 1997 11(2) ms β− 56Sc 0+
57Ca 20 37 56.99296(43)# 2009 8# ms [>620 ns] 5/2−#
58Ca 20 38 57.99836(54)# 2009 4# ms [>620 ns] 0+
59Ca 20 39 59.00624(64)# 2018 5# ms [>400 ns] 5/2−#
60Ca 20 40 60.01181(75)# 2018 2# ms [>400 ns] 0+
61Ca 20 41 61.02041(86)# (2025)[22][n 15] 1# ms 1/2−#
This table header & footer:
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  1. [1]
    ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  2. [2]
    Bold half-life – nearly stable, half-life longer than age of universe.
  3. [3]
    Modes of decay:
    EC:Electron capture
    n:Neutron emission
    p:Proton emission
  4. [4]
    Bold symbol as daughter – Daughter product is stable.
  5. [5]
    ( ) spin value – Indicates spin with weak assignment arguments.
  6. [6]
    # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  7. [7]
    Heaviest observationally stable nuclide with equal numbers of protons and neutrons
  8. [8]
    Believed to undergo double electron capture to 40Ar with a half-life no less than 1022 y
  9. [9]
    Cosmogenic nuclide
  10. [10]
    Believed to undergo β−β− decay to 46Ti
  11. [11]
    Primordial radionuclide
  12. [12]
    Believed to be capable of undergoing triple beta decay with very long partial half-life
  13. [13]
    Lightest nuclide known to undergo double beta decay
  14. [14]
    Theorized to also undergo β− decay to 48Sc with a partial half-life exceeding 1.1+0.8
    −0.6    ×1021 years[21]
  15. [15]
    Discovery of this isotope is unconfirmed

Calcium-48

Main article: Calcium-48
About 2 g of calcium-48

Calcium-48 is a doubly magic nucleus with 28 neutrons; unusually neutron-rich for a light primordial nucleus. It decays via double beta decay with an extremely long half-life of about 5.6×1019 years, though single beta decay is also theoretically possible. This decay can analyzed with the sd nuclear shell model, and it is more energetic (4.27 MeV) than any other double beta decay.[23] It is used as a precursor for neutron-rich[24] and superheavy[25] isotopes.

Calcium-60

Calcium-60 is the heaviest known isotope as of 2020.[1] First observed in 2018 at Riken alongside 59Ca and seven isotopes of other elements,[26] its existence suggests that there are additional even-N isotopes of calcium up to at least 70Ca, while 59Ca is probably the last bound isotope with odd N.[27] Earlier predictions had estimated the heaviest even isotope to be at 60Ca, and 59Ca unbound.[26]

In the neutron-rich region, N = 40 becomes a magic number, so 60Ca was considered early on to be a possibly doubly magic nucleus, as is observed for the 68Ni isotone.[28][29] However, subsequent spectroscopic measurements of the nearby nuclides 56Ca, 58Ca, and 62Ti instead predict that it should lie on the island of inversion known to exist around 64Cr.[29][30]

See also

Daughter products other than calcium

References

Further reading

External links

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