Activity determination of 231Pa by means of liquid scintillation counting

Abstract

Protactinium-231 decays through a chain of daughter nuclides to stable 207Pb, resulting in a number of alpha and beta transitions. A method based on liquid scintillation (LS) counting was developed to determine the activity concentration of 231Pa. For α emissions, the corresponding LS counting efficiency was assumed to be unity. A potential loss of the noble gas 219Rn was evaluated by an additional experiment. In the case of the short-lived 215Po, a dead-time-dependent correction factor was taken into account in the calculation. For beta emitters 227Ac, 223Fr, 211Pb and 207Tl, the counting efficiencies were determined by the CIEMAT/NIST efficiency tracing (CNET) method with 3H standard as a tracer. The impurities were checked and found that the possible impurity was 227Ac, with an initial activity ratio A(227Ac)/A (231Pa) between 0.5% and 0.8%. Finally, the activity concentration of the 231Pa solution was determined with a combined relative standard uncertainty of 0.39%.