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

Abstract

Authors describe the activity measurements undertaken at the CSIR’s National Metrology Laboratory on a solution of the pure beta emitting Radio nuclide phosphorus-32 that formed part of an international key comparison. Depending on the production mode, the pure beta-emitters 33P and 35S are possible impurities. Since exploratory source measurements indicated the presence of radioactive contaminants, the occurrence of both 33P and 35S was assumed. The method adopted to extract the 32P activity accurately was thus to follow the decay over an extended period of time, taking advantage of the different decay rates. The extracted counting rates were converted to activities by comparison/computation against 63Ni sources of known activity. The 32P activity was also independently given by the Triple-to-Double Coincidence Ratio efficiency calculation technique, after first correcting the double and triple count rates for the impurity contributions.