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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 t ...
(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 at ...
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 consi ...
41Ca, which has a
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 at ...
of 99,400 years. Unlike
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 ...
s that are produced in the atmosphere, 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 emit ...
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 E ...
sciences, the prevalence of 40Ca in nature has impeded its use in dating. Techniques using mass spectrometry 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. ...
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 ββ 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 , style="text-align:right" , 20 , style="text-align:right" , 28 , 47.95252290(10) , (6.4)×1019 y, , ββLightest 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


Further reading

* C. Michael Hogan. 2010
''Calcium''. ed. A. Jorgenson and C. Cleveland. ''Encyclopedia of Earth'', National Council for Science and the Environment, Washington, D.C.


External links


National Isotope Development Center Official website
{{Authority control Calcium
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 t ...