Isotopes of calcium

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 that are 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.

Isotopes of calcium (₂₀Ca)

Main isotopes Decay Isotope abun­dance half-life (t1/2) mode pro­duct ^40Ca 96.9% stable ^41Ca trace 9.94×10^4 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% 5.6×10^19 y β^−β^− ^48Ti
Standard atomic weight Ar°(Ca)
	40.078±0.004 40.078±0.004 (abridged)
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Stable ⁴⁰Ca comprises about 97% of natural calcium and is mainly created by nucleosynthesis in stars (alpha process). Similarly to ⁴⁰Ar, however, some atoms of ⁴⁰Ca are radiogenic, created through the 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 age 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 ⁴⁴Ca/⁴⁰Ca or ⁴⁴Ca/⁴²Ca, denoted as 'δ⁴⁴Ca' and 'δ^44/42Ca' 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

Nuclide	Z	N	Isotopic mass (Da)	Half-life	Decay mode	Daughter isotope	Spin and parity	Natural abundance (mole fraction)
								Normal proportion	Range of variation
^35Ca	20	15	35.00557(22)#	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)	100.9(13) ms	β^+, p (51.2%)	^35Ar	0+
					β^+ (48.8%)	^36K
^37Ca	20	17	36.98589785(68)	181.0(9) ms	β^+, p (76.8%)	^36Ar	3/2+
					β^+ (23.2%)	^37K
^38Ca	20	18	37.97631922(21)	443.70(25) ms	β^+	^38K	0+
^39Ca	20	19	38.97071081(64)	860.3(8) ms	β^+	^39K	3/2+
^40Ca	20	20	39.962590850(22)	Observationally stable			0+	0.9694(16)	0.96933–0.96947
^41Ca	20	21	40.96227791(15)	9.94(15)×10^4 y	EC	^41K	7/2−	Trace
^42Ca	20	22	41.95861778(16)	Stable			0+	0.00647(23)	0.00646–0.00648
^43Ca	20	23	42.95876638(24)	Stable			7/2−	0.00135(10)	0.00135–0.00135
^44Ca	20	24	43.95548149(35)	Stable			0+	0.0209(11)	0.02082–0.02092
^45Ca	20	25	44.95618627(39)	162.61(9) d	β^−	^45Sc	7/2−
^46Ca	20	26	45.9536877(24)	Observationally stable			0+	4×10^−5	4×10^−5–4×10^−5
^47Ca	20	27	46.9545411(24)	4.536(3) d	β^−	^47Sc	7/2−
^48Ca	20	28	47.952522654(18)	5.6(10)×10^19 y	β^−β^−	^48Ti	0+	0.00187(21)	0.00186–0.00188
^49Ca	20	29	48.95566263(19)	8.718(6) min	β^−	^49Sc	3/2−
^50Ca	20	30	49.9574992(17)	13.45(5) s	β^−	^50Sc	0+
^51Ca	20	31	50.96099566(56)	10.0(8) s	β^−	^51Sc	3/2−
^52Ca	20	32	51.96321365(72)	4.6(3) s	β^− (>98%)	^52Sc	0+
					β^−, n (<2%)	^51Sc
^53Ca	20	33	52.968451(47)	461(90) ms	β^− (60%)	^53Sc	1/2−#
					β^−, n (40%)	^52Sc
^54Ca	20	34	53.972989(52)	90(6) ms	β^−	^54Sc	0+
^55Ca	20	35	54.97998(17)	22(2) ms	β^−	^55Sc	5/2−#
^56Ca	20	36	55.98550(27)	11(2) ms	β^−	^56Sc	0+
^57Ca	20	37	56.99296(43)#	8# ms [>620 ns]			5/2−#
^58Ca	20	38	57.99836(54)#	4# ms [>620 ns]			0+
^59Ca	20	39	59.00624(64)#	5# ms [>400 ns]			5/2−#
^60Ca	20	40	60.01181(75)#	2# ms [>400 ns]			0+
^61Ca	20	41	61.02041(86)#	1# ms			1/2−#
This table header & footer: view

1. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
2. Bold half-life – nearly stable, half-life longer than age of universe.
3. Modes of decay:

   EC:	Electron capture
   n:	Neutron emission
   p:	Proton emission

4. Bold symbol as daughter – Daughter product is stable.
5. ( ) spin value – Indicates spin with weak assignment arguments.
6. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
7. Heaviest observationally stable nuclide with equal numbers of protons and neutrons
8. Believed to undergo double electron capture to ⁴⁰Ar with a half-life no less than 10²² y
9. Cosmogenic nuclide
10. Believed to undergo β⁻β⁻ decay to ⁴⁶Ti
11. Primordial radionuclide
12. Believed to be capable of undergoing triple beta decay with very long partial half-life
13. Lightest nuclide known to undergo double beta decay
14. Theorized to also undergo β⁻ decay to ⁴⁸Sc with a partial half-life exceeding 1.1^+0.8
    _−0.6×10²¹ years
15. Discovery of this isotope is unconfirmed

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. It is used as a precursor for neutron-rich and superheavy isotopes.

Calcium-60

Calcium-60 is the heaviest known isotope as of 2020^[update]. First observed in 2018 at Riken alongside ⁵⁹Ca and seven isotopes of other elements, 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. Earlier predictions had estimated the heaviest even isotope to be at ⁶⁰Ca, and ⁵⁹Ca unbound.

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. 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.

See also

Daughter products other than calcium

• Isotopes of titanium
• Isotopes of scandium
• Isotopes of potassium
• Isotopes of argon