K-A decay

K-A decay

[′kā′ā di‚kā]
(nuclear physics)
Radioactive decay of potassium-40 (40K) to argon-40 (40A), as the nucleus of potassium captures an orbital electron and then decays to argon-40; the ratio of 40K to 40A is used to determine the age of rock (K-A age).