Calcium Calcium is a chemical element with the 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 ...

(₂₀Ca) has 26 known isotopes, ranging from ³⁵Ca to ⁶⁰Ca. There are five

stable isotope The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element. Hence, the plural form stable isotopes usually refers to isotopes of the same element. The relative abundanc ...

s (⁴⁰Ca, ⁴²Ca, ⁴³Ca, ⁴⁴Ca and ⁴⁶Ca), plus one isotope ( ⁴⁸Ca) with such a long

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...

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 Cosmogenic nuclides (or cosmogenic isotopes) are rare nuclides (isotopes) created when a high-energy cosmic ray interacts with the atomic nucleus, nucleus of an ''in situ'' Solar System atom, causing nucleons (protons and neutrons) to be expelled ...

radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...

⁴¹Ca, which has a

of 99,400 years. Unlike

s that are produced in the

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...

, ⁴¹Ca is produced by

neutron activation Neutron activation is the process in which neutron radiation induces radioactivity in materials, and occurs when atomic nuclei capture free neutrons, becoming heavier and entering excited states. The excited nucleus decays immediately by emittin ...

of ⁴⁰Ca. Most of its production is in the upper metre 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. 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 Potassium–argon dating, abbreviated K–Ar dating, is a radiometric dating method used in geochronology and archaeology. It is based on measurement of the product of the radioactive decay of an isotope of potassium (K) into argon (Ar). Potassium ...

has been used extensively in the

geological Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Eart ...

sciences, the prevalence of ⁴⁰Ca in nature has impeded its use in dating. Techniques using

mass spectrometry Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a ''mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is use ...

and a double spike isotope dilution have been used for K–Ca age dating.

List of isotopes

, - , rowspan=2, ³⁵Ca , rowspan=2 style="text-align:right" , 20 , rowspan=2 style="text-align:right" , 15 , rowspan=2, 35.00514(21)# , rowspan=2, 25.7(2) ms , β⁺, p (95.9%) , ³⁴Ar , rowspan=2, 1/2+# , rowspan=2, , rowspan=2, , - , β⁺, 2p (4.1%) , ³³Cl , - , rowspan=2, ³⁶Ca , rowspan=2 style="text-align:right" , 20 , rowspan=2 style="text-align:right" , 16 , rowspan=2, 35.99307(4) , rowspan=2, 101.2(15) ms , β⁺, p (51.2%) , ³⁵Ar , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁺ (48.8%) , ³⁶K , - , rowspan=2, ³⁷Ca , rowspan=2 style="text-align:right" , 20 , rowspan=2 style="text-align:right" , 17 , rowspan=2, 36.9858979(7) , rowspan=2, 181.1(10) ms , β⁺, p (82.1%) , ³⁶Ar , rowspan=2, 3/2+# , rowspan=2, , rowspan=2, , - , β⁺ (17.9%) , ³⁷K , - , ³⁸Ca , style="text-align:right" , 20 , style="text-align:right" , 18 , 37.97631923(21) , 443.70(25) ms , β⁺ , ³⁸K , 0+ , , , - , ³⁹Ca , style="text-align:right" , 20 , style="text-align:right" , 19 , 38.9707108(6) , 860.3(8) ms , β⁺ , ³⁹K , 3/2+ , , , - , ⁴⁰CaHeaviest nuclide with equal numbers of protons and neutrons with no observed decay , style="text-align:right" , 20 , style="text-align:right" , 20 , 39.962590866(22) , colspan=3 align=center,

Observationally Stable Stable nuclides are nuclides that are not radioactive and so (unlike radionuclides) do not spontaneously undergo radioactive decay. When such nuclides are referred to in relation to specific elements, they are usually termed stable isotopes. Th ...

Believed to undergo

double electron capture Double electron capture is a decay mode of an atomic nucleus. For a nuclide (''A'', ''Z'') with a number of nucleons ''A'' and atomic number ''Z'', double electron capture is only possible if the mass of the nuclide (''A'', ''Z''−2) is lower. I ...

to ⁴⁰Ar with a half-life no less than 5.9×10²¹ y , 0+ , 0.96941(156) , 0.96933–0.96947 , - , ⁴¹Ca , style="text-align:right" , 20 , style="text-align:right" , 21 , 40.96227792(15) , 9.94(15)×10⁴ y , EC , ⁴¹K , 7/2− , Trace

Cosmogenic nuclide Cosmogenic nuclides (or cosmogenic isotopes) are rare nuclides (isotopes) created when a high-energy cosmic ray interacts with the nucleus of an ''in situ'' Solar System atom, causing nucleons (protons and neutrons) to be expelled from the atom ( ...

, , - , ⁴²Ca , style="text-align:right" , 20 , style="text-align:right" , 22 , 41.95861783(16) , colspan=3 align=center, Stable , 0+ , 0.00647(23) , 0.00646–0.00648 , - , ⁴³Ca , style="text-align:right" , 20 , style="text-align:right" , 23 , 42.95876643(24) , colspan=3 align=center, Stable , 7/2− , 0.00135(10) , 0.00135–0.00135 , - , ⁴⁴Ca , style="text-align:right" , 20 , style="text-align:right" , 24 , 43.9554815(3) , colspan=3 align=center, Stable , 0+ , 0.02086(110) , 0.02082–0.02092 , - , ⁴⁵Ca , style="text-align:right" , 20 , style="text-align:right" , 25 , 44.9561863(4) , 162.61(9) d , β⁻ , ⁴⁵Sc , 7/2− , , , - , ⁴⁶Ca , style="text-align:right" , 20 , style="text-align:right" , 26 , 45.9536880(24) , colspan=3 align=center, Observationally StableBelieved to undergo β⁻β⁻ decay to ⁴⁶Ti with a half-life no less than 2.8×10¹⁵ y , 0+ , 4(3)×10⁻⁵ , 4×10⁻⁵–4×10⁻⁵ , - , ⁴⁷Ca , style="text-align:right" , 20 , style="text-align:right" , 27 , 46.9545414(24) , 4.536(3) d , β⁻ , ⁴⁷Sc , 7/2− , , , - , ⁴⁸Ca Primordial

radionuclide A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transfer ...

, style="text-align:right" , 20 , style="text-align:right" , 28 , 47.95252290(10) , (6.4)×10¹⁹ y, , β⁻β⁻Lightest nuclide known to undergo

double beta decay In nuclear physics, double beta decay is a type of radioactive decay in which two neutrons are simultaneously transformed into two protons, or vice versa, inside an atomic nucleus. As in single beta decay, this process allows the atom to move clos ...

, ⁴⁸Ti , 0+ , 0.00187(21) , 0.00186–0.00188 , - , ⁴⁹Ca , style="text-align:right" , 20 , style="text-align:right" , 29 , 48.95562288(22) , 8.718(6) min , β⁻ , ⁴⁹Sc , 3/2− , , , - , ⁵⁰Ca , style="text-align:right" , 20 , style="text-align:right" , 30 , 49.9574992(17) , 13.9(6) s , β⁻ , ⁵⁰Sc , 0+ , , , - , ⁵¹Ca , style="text-align:right" , 20 , style="text-align:right" , 31 , 50.9609957(6) , 10.0(8) s , β⁻ , ⁵¹Sc , (3/2−) , , , - , rowspan=2, ⁵²Ca , rowspan=2 style="text-align:right" , 20 , rowspan=2 style="text-align:right" , 32 , rowspan=2, 51.9632136(7) , rowspan=2, 4.6(3) s , β⁻ (98%) , ⁵²Sc , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁻, n (2%) , ⁵¹Sc , - , rowspan=2, ⁵³Ca , rowspan=2 style="text-align:right" , 20 , rowspan=2 style="text-align:right" , 33 , rowspan=2, 52.96845(5) , rowspan=2, 461(90) ms , β⁻ (60%) , ⁵³Sc , rowspan=2, 3/2−# , rowspan=2, , rowspan=2, , - , β⁻, n (40%) , ⁵²Sc , - , rowspan=2, ⁵⁴Ca , rowspan=2 style="text-align:right" , 20 , rowspan=2 style="text-align:right" , 34 , rowspan=2, 53.97299(5) , rowspan=2, 90(6) ms , β⁻ (93%) , ⁵⁴Sc , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁻, n (7%) , ⁵³Sc , - , ⁵⁵Ca , style="text-align:right" , 20 , style="text-align:right" , 35 , 54.98030(32)# , 22(2) ms , β⁻ , ⁵⁵Sc , 5/2−# , , , - , ⁵⁶Ca , style="text-align:right" , 20 , style="text-align:right" , 36 , 55.98508(43)# , 11(2) ms , β⁻ , ⁵⁶Sc , 0+ , , , - , rowspan=2, ⁵⁷Ca , rowspan=2 style="text-align:right" , 20 , rowspan=2 style="text-align:right" , 37 , rowspan=2, 56.99262(43)# , rowspan=2, 5# ms , β⁻ , ⁵⁷Sc , rowspan=2, 5/2−# , rowspan=2, , rowspan=2, , - , β⁻, n , ⁵⁶Sc , - , rowspan=2, ⁵⁸Ca , rowspan=2 style="text-align:right" , 20 , rowspan=2 style="text-align:right" , 38 , rowspan=2, 57.99794(54)# , rowspan=2, 3# ms , β⁻ , ⁵⁸Sc , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁻, n , ⁵⁷Sc , - , ⁵⁹Ca , style="text-align:right" , 20 , style="text-align:right" , 39 , , , β⁻ , ⁵⁹Sc , , , , - , ⁶⁰Ca , style="text-align:right" , 20 , style="text-align:right" , 40 , , , β⁻ , ⁶⁰Sc , 0+ , ,

References

External links

National Isotope Development Center Official website
{{Authority control Calcium

List of isotopes

References

Further reading

External links