Activity measurement of phosphorus-32 in the presence of pure beta-emitting impurities

Abstract

Activity measurements undertaken at the CSIR's National Metrology Laboratory (NML) on a solution of the pure beta-emitting radionuclide phosphorus-32, which formed part of an international key comparison, are described. Since exploratory source measurements indicated the presence of radioactive impurities, the occurrence of the pure beta-emitters phosphorus-33 and sulphur-35 was assumed. The method adopted to extract the phosphorus-32 activity was thus to follow the decay over an extended period of time. The extracted counting rates were converted to activities by comparison/computation against a 63Ni source of known activity. The phosphorus-32 activity was also independently given by the Triple-to-Double Coincidence Ratio (TDCR) efficiency calculation technique, after first correcting the double and triple count rates for the impurity contributions