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Isotopes of calcium

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Calcium (Ca) has 26 known isotopes, ranging from Ca to Ca. There are five stable isotopes (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 geological 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 similar in method to Rb-Sr dating, as well as determining K losses from the lower continental crust and for source-tracing calcium contributions from various geologic reservoirs.

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 to quantifying volcanic eruption timescales. Other applications include: quantifying carbon sequestration efficiency in CO2 injection sites and understanding ocean acidification, exploring both ubiquitous and rare magmatic processes, such as formation of granites and carbonatites, tracing modern and ancient trophic webs including in dinosaurs, assessing weaning practices in ancient humans, and a plethora of other emerging applications.

List of isotopes

Calcium-33

|-id=Calcium-35 | β, p (95.8%)

Ar
β, 2p (4.2%)
Cl
-
β (rare)
K
-id=Calcium-36
β, p (51.2%)
Ar
-
β (48.8%)
K
-id=Calcium-37
β, p (76.8%)
Ar
-
β (23.2%)
K
-id=Calcium-38
Ca
37.97631922(21)
443.70(25) ms
β
K
0+

| | |-id=Calcium-39 | Ca | 38.97071081(64) | 860.3(8) ms | β | K | 3/2+ | | |-id=Calcium-40 | CaHeaviest observationally stable nuclide with equal numbers of protons and neutrons | 39.962590850(22) | 0+ | 0.9694(16) | 0.96933–0.96947 |-id=Calcium-41 | Ca | 40.96227791(15) | 9.94(15)×10 y | EC | K | 7/2− | TraceCosmogenic nuclide | |-id=Calcium-42 | Ca | 41.95861778(16) | 0+ | 0.00647(23) | 0.00646–0.00648 |-id=Calcium-43 | Ca | 42.95876638(24) | 7/2− | 0.00135(10) | 0.00135–0.00135 |-id=Calcium-44 | Ca | 43.95548149(35) | 0+ | 0.0209(11) | 0.02082–0.02092 |-id=Calcium-45 | Ca | 44.95618627(39) | 162.61(9) d | β | Sc | 7/2− | | |-id=Calcium-46 | Ca | 45.9536877(24) | 0+ | 4×10 | 4×10–4×10 |-id=Calcium-47 | Ca | 46.9545411(24) | 4.536(3) d | β | Sc | 7/2− | | |- | CaPrimordial radionuclideBelieved to be capable of undergoing triple beta decay with very long partial half-life | 47.952522654(18) | 5.6(10)×10 y | ββLightest nuclide known to undergo double beta decay | Ti | 0+ | 0.00187(21) | 0.00186–0.00188 |-id=Calcium-49 | Ca | 48.95566263(19) | 8.718(6) min | β | Sc | 3/2− | | |-id=Calcium-50 | Ca | 49.9574992(17) | 13.45(5) s | β | Sc | 0+ | | |-id=Calcium-51 | Ca | 50.96099566(56) | 10.0(8) s | β | Sc | 3/2− | | |-id=Calcium-52 | β (98%)

Sc
β, n (
Sc
-id=Calcium-53
β (60%)
Sc
-
β, n (40%)
Sc
-id=Calcium-54
Ca
53.972989(52)
90(6) ms
β
Sc
0+

| | |-id=Calcium-55 | Ca | 54.97998(17) | 22(2) ms | β | Sc | 5/2−# | | |-id=Calcium-56 | Ca | 55.98550(27) | 11(2) ms | β | Sc | 0+ | | |-id=Calcium-57 | Ca | 56.99296(43)# | 8# ms [620 ns] | | | 5/2−# | | |-id=Calcium-58 | Ca | 57.99836(54)# | 4# ms [620 ns] | | | 0+ | | |-id=Calcium-59 | Ca | 59.00624(64)# | 5# ms [400 ns] | | | 5/2−# | | |- | Ca | 60.01181(75)# | 2# ms [400 ns] | | | 0+ | | |-id=Calcium-61 | 61CaDiscovery of this isotope is unconfirmed | 61.02041(86)# | 1# ms | | | 1/2−# |

Calcium-48

Main article: 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. However, subsequent spectroscopic measurements of the nearby nuclides Ca, Ca, and Ti instead predict that it should lie on the island of inversion known to exist around Cr.

References

(1982-12-01). "Precise age determinations and petrogenetic studies using the KCa method". Geochimica et Cosmochimica Acta.
admin. (18 January 2023). "K-Ca dating and Ca isotope composition of the oldest Solar System lava, Erg Chech 002". Geochemical Perspectives Letters.
admin. (6 February 2019). "Radiogenic Ca isotopes confirm post-formation K depletion of lower crust {{!}} Geochemical Perspectives Letters". Geochemical Perspectives Letters.
(2021-09-16). "Radiogenic 40 Ca in Seawater: Implications for Modern and Ancient Ca Cycles". ACS Earth and Space Chemistry.
(2022-12-01). "Decoupling of physical and chemical erosion in the Himalayas revealed by radiogenic Ca isotopes". Geochimica et Cosmochimica Acta.
(2019-06-01). "Calcium isotope ratios in blood and urine: A new biomarker for the diagnosis of osteoporosis". Bone Reports.
(2019-10-08). "Ca isotopes record rapid crystal growth in volcanic and subvolcanic systems". Proceedings of the National Academy of Sciences.
(2019-04-30). "Rapid CO2 mineralisation into calcite at the CarbFix storage site quantified using calcium isotopes". Nature Communications.
(2020-08-05). "Towards an understanding of the Ca isotopic signal related to ocean acidification and alkalinity overshoots in the rock record". Chemical Geology.
(2023-04-15). "Granite petrogenesis and the δ44Ca of continental crust". Earth and Planetary Science Letters.
admin. (December 2023). "Calcium isotope fractionation during melt immiscibility and carbonatite petrogenesis {{!}} Geochemical Perspectives Letters". Geochemical Perspectives Letters.
(1997-06-01). "Biological control of calcium isotopic abundances in the global calcium cycle". Geochimica et Cosmochimica Acta.
admin. (26 April 2019). "Calcium stable isotopes place Devonian conodonts as first level consumers {{!}} Geochemical Perspectives Letters". Geochemical Perspectives Letters.
(2018-04-11). "Calcium isotopes offer clues on resource partitioning among Cretaceous predatory dinosaurs". Proceedings of the Royal Society B: Biological Sciences.
(2017-06-13). "Assessing human weaning practices with calcium isotopes in tooth enamel". Proceedings of the National Academy of Sciences.
(1999). "Shell-model study of the highly forbidden beta decay {{sup". [[EPL (journal).
(4 September 2025). "Discovery of new isotopes in the fragmentation of Se 82 and insights into their production". Physical Review C.
Balysh, A.. (1996). "Double Beta Decay of {{sup". Physical Review Letters.
Notani, M.. (2002). "New neutron-rich isotopes, {{sup". Physics Letters B.
Oganessian, Yu. Ts.. (October 2006). "Synthesis of the isotopes of elements 118 and 116 in the {{sup". Physical Review C.
(11 July 2018). "Discovery of {{sup". Physical Review Letters.
(14 February 2019). "Neutron Drip Line in the Ca Region from Bayesian Model Averaging". Physical Review Letters.
(21 March 2014). "Nuclear Structure Towards ''N'' = 40 {{sup". Physical Review Letters.
(January 2020). "Shell evolution of ''N'' = 40 isotones towards {{sup". Physics Letters B.
(August 2023). "Level structures of {{sup". Physics Letters B.

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