Isotopes of calcium

Calcium (Ca) has 24 isotopes, from ³⁴Ca to ⁵⁷Ca. There are five stable isotopes (⁴⁰Ca, ⁴²Ca, ⁴³Ca, ⁴⁴Ca and ⁴⁶Ca), plus one isotope (⁴⁸Ca) with such a long half-life 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, radioactive ⁴¹Ca, which has a half-life of 102,000 years. Unlike cosmogenic isotopes that are produced in the atmosphere, ⁴¹Ca is produced by neutron activation of ⁴⁰Ca. Most of its production is in the upper metre or so 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 radioisotope is ⁴⁵Ca, with a half-life of 163 days.

All other isotopes have half-lives of 163 days or less, most under a minute. The least stable is ³⁴Ca with a half-life shorter than 35 nanoseconds.