Potassium-40 is a long-lived radioactive isotope with 19 protons and 21 neutrons. It can decay to calcium-40 through beta-minus decay, or to argon-40 through electron capture and a rare beta-plus decay. The argon-producing branch supports potassium-argon dating.
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Potassium-40 (K-40 or ^40K) is a naturally occurring isotope of potassium, which is a vital nutrient for various biological and geological processes. It is one of the three stable isotopes of potassium, alongside Potassium-39 (^39K) and Potassium-41 (^41K). K-40 is notable because it is radioactive and has a long half-life of about 1.248 billion years, which means it decays very slowly.