Page "Calcium" Paragraph 17

Calcium has four stable isotopes (< sup > 40 </ sup > Ca, < sup > 42 </ sup > Ca, < sup > 43 </ sup > Ca and < sup > 44 </ sup > Ca ), plus two more isotopes (< sup > 46 </ sup > Ca and < sup > 48 </ sup > Ca ) that have such long half-lives that for all practical purposes they also can be considered stable.

The 20 % range in relative mass among naturally occurring calcium isotopes is greater than for any element except hydrogen and helium.

Calcium also has a cosmogenic isotope, radioactive < sup > 41 </ sup > Ca, which has a half-life of 103, 000 years.

Unlike cosmogenic isotopes that are produced in the atmosphere, < sup > 41 </ sup > Ca is produced by neutron activation of < sup > 40 </ sup > Ca.

Most of its production is in the upper metre or so of the soil column, where the cosmogenic neutron flux is still sufficiently strong.

< sup > 41 </ sup > Ca has received much attention in stellar studies because it decays to < sup > 41 </ sup > K, a critical indicator of solar-system anomalies.