The correction usually applied to an SIR measurement in the presence of a g
amma-ray emitting impurity is presented and explained. The method of calibr
ation of a Ge(Li) spectrometer is briefly described. It is used to look for
impurities when SIR measurements show inconsistencies. An example is prese
nted where a Ru-103 impurity was discovered in a Mo-99 solution. The correc
tion applied compensates for the decrease of around 0.2% per day observed i
n the SIR measurements of this Mo-99 ampoule. (C) 2000 Published by Elsevie
r Science Ltd. All rights reserved.