Calcium (Ca) has 26 known isotopes, ranging from Ca to Ca. There are five (Ca, Ca, Ca, Ca and Ca), plus one isotope (Ca) with such a long half-life that it is for all practical purposes stable. The most abundant isotope, Ca, as well as the rare Ca, are theoretically unstable on energetic grounds, but their decay has not been observed. Calcium also has a cosmogenic isotope, Ca, with half-life 99,400 years. Unlike cosmogenic isotopes produced in the air, Ca is produced by neutron activation of solid Ca 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 Ca with half-life 162.61 days and Ca with half-life 4.536 days. All other calcium isotopes have half-lives of minutes or less.
Ca comprises about 97% of natural calcium and is mainly created by nucleosynthesis in stars (alpha process). Like Ar, however, some Ca is radiogenic, created by radioactive decay of K. While K–Ar dating has been used extensively in the geology sciences, the prevalence of Ca 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
Stable isotope variations of calcium (most typically Ca/Ca or Ca/Ca, denoted 'δCa' and 'δCa' in delta notation) are also widely used across the natural sciences for a number of applications, ranging from early determination of osteoporosis
List of isotopes
|-id=Calcium-35
| rowspan=3|Ca
| rowspan=3 style="text-align:right" | 20
| rowspan=3 style="text-align:right" | 15
| rowspan=3|35.00557(22)#
| rowspan=3|25.7(2) ms
|
Beta decay,
proton emission (95.8%)
| Ar
| rowspan=3|1/2+#
| rowspan=3|
| rowspan=3|
|-
| β, 2p (4.2%)
| Cl
|-
| β (rare)
| K
|-id=Calcium-36
| rowspan=2|Ca
| rowspan=2 style="text-align:right" | 20
| rowspan=2 style="text-align:right" | 16
| rowspan=2|35.993074(43)
| rowspan=2|100.9(13) ms
| β, p (51.2%)
| Ar
| rowspan=2|0+
| rowspan=2|
| rowspan=2|
|-
| β (48.8%)
| K
|-id=Calcium-37
| rowspan=2|Ca
| rowspan=2 style="text-align:right" | 20
| rowspan=2 style="text-align:right" | 17
| rowspan=2|36.98589785(68)
| rowspan=2|181.0(9) ms
| β, p (76.8%)
|
Ar
| rowspan=2|3/2+
| rowspan=2|
| rowspan=2|
|-
| β (23.2%)
| K
|-id=Calcium-38
| Ca
| style="text-align:right" | 20
| style="text-align:right" | 18
| 37.97631922(21)
| 443.70(25) ms
| β
| K
| 0+
|
|
|-id=Calcium-39
| Ca
| style="text-align:right" | 20
| style="text-align:right" | 19
| 38.97071081(64)
| 860.3(8) ms
| β
|
K
| 3/2+
|
|
|-id=Calcium-40
| Ca
[Heaviest observationally stable nuclide with equal numbers of protons and neutrons]
| style="text-align:right" | 20
| style="text-align:right" | 20
| 39.962590850(22)
| colspan=3 align=center|
Observationally stable[Believed to undergo double electron capture to Ar with a half-life no less than 10 y]
| 0+
| 0.9694(16)
| 0.96933–0.96947
|-id=Calcium-41
| Ca
| style="text-align:right" | 20
| style="text-align:right" | 21
| 40.96227791(15)
| 9.94(15)×10 y
|
electron capture
|
K
| 7/2−
| Trace
[Cosmogenic nuclide]
|
|-id=Calcium-42
| Ca
| style="text-align:right" | 20
| style="text-align:right" | 22
| 41.95861778(16)
| colspan=3 align=center|
Stable
| 0+
| 0.00647(23)
| 0.00646–0.00648
|-id=Calcium-43
| Ca
| style="text-align:right" | 20
| style="text-align:right" | 23
| 42.95876638(24)
| colspan=3 align=center|
Stable
| 7/2−
| 0.00135(10)
| 0.00135–0.00135
|-id=Calcium-44
| Ca
| style="text-align:right" | 20
| style="text-align:right" | 24
| 43.95548149(35)
| colspan=3 align=center|
Stable
| 0+
| 0.0209(11)
| 0.02082–0.02092
|-id=Calcium-45
| Ca
| style="text-align:right" | 20
| style="text-align:right" | 25
| 44.95618627(39)
| 162.61(9) d
| β
|
Sc
| 7/2−
|
|
|-id=Calcium-46
| Ca
| style="text-align:right" | 20
| style="text-align:right" | 26
| 45.9536877(24)
| colspan=3 align=center|
Observationally stable[Believed to undergo ββ decay to Ti]
| 0+
| 4×10
| 4×10–4×10
|-id=Calcium-47
| Ca
| style="text-align:right" | 20
| style="text-align:right" | 27
| 46.9545411(24)
| 4.536(3) d
| β
| Sc
| 7/2−
|
|
|-
| Ca
[Primordial radionuclide][Believed to be capable of undergoing triple beta decay with very long partial half-life]
| style="text-align:right" | 20
| style="text-align:right" | 28
| 47.952522654(18)
|
5.6(10)×10 y
| ββ
[Lightest nuclide known to undergo double beta decay]
|
Ti
| 0+
| 0.00187(21)
| 0.00186–0.00188
|-id=Calcium-49
| Ca
| style="text-align:right" | 20
| style="text-align:right" | 29
| 48.95566263(19)
| 8.718(6) min
| β
| Sc
| 3/2−
|
|
|-id=Calcium-50
| Ca
| style="text-align:right" | 20
| style="text-align:right" | 30
| 49.9574992(17)
| 13.45(5) s
| β
| Sc
| 0+
|
|
|-id=Calcium-51
| Ca
| style="text-align:right" | 20
| style="text-align:right" | 31
| 50.96099566(56)
| 10.0(8) s
| β
| Sc
| 3/2−
|
|
|-id=Calcium-52
| rowspan=2|Ca
| rowspan=2 style="text-align:right" | 20
| rowspan=2 style="text-align:right" | 32
| rowspan=2|51.96321365(72)
| rowspan=2|4.6(3) s
| β (>98%)
| Sc
| rowspan=2|0+
| rowspan=2|
| rowspan=2|
|-
| β, n (<2%)
| Sc
|-id=Calcium-53
| rowspan=2|Ca
| rowspan=2 style="text-align:right" | 20
| rowspan=2 style="text-align:right" | 33
| rowspan=2|52.968451(47)
| rowspan=2|461(90) ms
| β (60%)
| Sc
| rowspan=2|1/2−#
| rowspan=2|
| rowspan=2|
|-
| β, n (40%)
| Sc
|-id=Calcium-54
| Ca
| style="text-align:right" | 20
| style="text-align:right" | 34
| 53.972989(52)
| 90(6) ms
| β
| Sc
| 0+
|
|
|-id=Calcium-55
| Ca
| style="text-align:right" | 20
| style="text-align:right" | 35
| 54.97998(17)
| 22(2) ms
| β
| Sc
| 5/2−#
|
|
|-id=Calcium-56
| Ca
| style="text-align:right" | 20
| style="text-align:right" | 36
| 55.98550(27)
| 11(2) ms
| β
| Sc
| 0+
|
|
|-id=Calcium-57
| Ca
| style="text-align:right" | 20
| style="text-align:right" | 37
| 56.99296(43)#
| 8# ms >620 ns
|
|
| 5/2−#
|
|
|-id=Calcium-58
| Ca
| style="text-align:right" | 20
| style="text-align:right" | 38
| 57.99836(54)#
| 4# ms >620 ns
|
|
| 0+
|
|
|-id=Calcium-59
| Ca
| style="text-align:right" | 20
| style="text-align:right" | 39
| 59.00624(64)#
| 5# ms >400 ns
|
|
| 5/2−#
|
|
|-
| Ca
| style="text-align:right" | 20
| style="text-align:right" | 40
| 60.01181(75)#
| 2# ms >400 ns
|
|
| 0+
|
|
|-id=Calcium-61
|
61Ca
[Discovery of this isotope is unconfirmed]
| style="text-align:right" | 20
| style="text-align:right" | 41
| 61.02041(86)#
| 1# ms
|
|
| 1/2−#
|
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 5.6×10 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.
It is used as a precursor for neutron-rich
and superheavy
isotopes.
Calcium-60
Calcium-60 is the heaviest known isotope .
First observed in 2018 at
Riken alongside Ca and seven isotopes of other elements,
its existence suggests that there are additional even-
N isotopes of calcium up to at least Ca, while Ca is probably the last bound isotope with odd
N.
Earlier predictions had estimated the heaviest even isotope to be at Ca, and Ca unbound.
In the neutron-rich region, N = 40 becomes a magic number, so Ca was considered early on to be a possibly doubly magic nucleus, as is observed for the Ni isotone.
See also
Daughter products other than calcium
-
Isotopes of titanium
-
Isotopes of scandium
-
Isotopes of potassium
-
Isotopes of argon
Further reading
External links
