Argon^(40):Potassium^(40) Dating

The element potassium has three naturally occurring isotopes, potassium^(39), potassium^(40), and potassium^(41), with atomic abundances of 93.08, 0.0119, and 6.9, respectively (Nier, 1950). Of these, potassium^(40) is radioactive with a decay constant λ = 0.55 X 10^(-9) year^(-1) (see Birch, 1951; Burch, 1953). Potassium^(40) decays by K-electron capture to argon^(40) with the emission of a gamma and by beta emission to calcium^(40) (see Figure 3.1)