Half-life determination and comparison of activity standards of 231Pa

Abstract The results of an international comparison of activity measurements of a solution of 231Pa are reported and analysed. Prior to this, no known standardisation of 231Pa by activity measurement had been carried out. The comparison was run in 2017-2018 involving eight laboratories, and returned results with no identifiable inconsistencies between methods or laboratories. The results, including one mass determination, gave a231Pa activity concentration of 41.461(48) kBq g−1 and a231Pa atom concentration of 61.48(23) × 1015 atoms g−1, from which a half-life value of 32 570(130) years was derived.