Influence of radioactive impurities on SIR measurements

The correction usually applied to an SIR measurement in the presence of a gamma-ray emitting impurity is presented and explained. The method of calibration of a Ge(Li) spectrometer is briefly described. It is used to look for impurities when SIR measurements show inconsistencies. An example is presented where a 103Ru impurity was discovered in a 99Mo solution. The correction applied compensates for the decrease of around 0.2% per day observed in the SIR measurements of this 99Mo ampoule.