structural:scholar_edition
Potassium-40 (⁴⁰K) is a radioactive isotope of potassium which has a long half-life of 1.25 billion years. It makes up about 0.012% of the total amount of potassium found in nature. Potassium-40 undergoes three types of radioactive decay. In about 89.28% of events, it decays to calcium-40 (⁴⁰Ca) with emission of a beta particle with a maximum energy of 1.31 MeV and an antineutrino. In about 10.72% of events, it decays to argon-40 (⁴⁰Ar) by electron capture (EC), with the emission of a neutrino and then a 1.460 MeV gamma ray. The radioactive decay of this particular isotope explains the large abundance of argon in the Earth's atmosphere, as well as prevalence of ⁴⁰Ar over other isotopes. Very rarely, it decays to ⁴⁰Ar by emitting a positron (β+) and a neutrino.