Ar/Ar Geochronology Laboratory

The ⁴⁰Ar/³⁹Ar dating method is a modification/improvement of the ⁴⁰K-⁴⁰Ar method. The utilised decay system is the electron capture by a ⁴⁰K parent nuclide and the production of a ⁴⁰Ar daughter nuclide with a decay constant (Λe) of 0.581 x 10⁻¹⁰. In addition, beta-decay of ⁴⁰K to ⁴⁰Ca also occurs with a decay constant (Λb) of 4.96 x 10⁻¹⁰, but this branch is not used. For the K-Ar method, direct determination of potassium concentrations on sample aliquots is necessary. In contrast, for the ⁴⁰Ar/³⁹Ar dating method potassium concentrations are determined indirectly by irradiating the rock or mineral samples in a flux of fast neutrons in a nuclear reactor, resulting in the ³⁹K(n,p)³⁹Ar reaction which produces ³⁹Ar nuclides.