Half-life determination of 40K by LSC

The long-lived radioisotope 40K is one of the isotopes applied by geologists to date rocks hundreds or even thousands of millions of years old. Knowing the half-life of 40K, the potassium–argon (K–Ar) method gives an estimate of the date of the rockʹs formation by measuring the quantity of the daughter stable isotope 40Ar. As in the case of other radiometric methods, the results of the K–Ar dating method are generally accompanied by an error estimate, which includes the counting process, the uncertainty in the half-life of 40K and the beta to capture branching ratio. The objectives of this paper are basically three. First, we describe a procedure to incorporate the largest amount of the potassium cations into the liquid scintillator cocktail. This time, gels are able to provide much higher counting rates than the background. Second, Cerenkov counting gives the best shapefactor for 40K β-ray transitions. Third, the CIEMAT/NIST method determines the activity of the samples and an averaged half-life for the radionuclide.