Standardisation of 56Co and 57Co using software coincidence counting system

Activities of the radionuclides 56Co and 57Co were determined by the efficiency extrapolation method applied to 4π(PC)-γ coincidence counting. Solutions of 56Co usually contain a significant amount of 57Co and 58Co, so the measured activity of 56Co requires correction. When the conventional coincidence method is used for 56Co standardisation, the corrections are derived from the dependence of Proportional Counter (PC) detection efficiencies for 57Co and 56Co measured using sources with mixture of 56Co and 57Co, which is complicated. These difficulties were reduced by means of a software coincidence method, with a HPGe detector in gamma channel, where the detection efficiencies were evaluated directly from the records of coincidence measurements of standardised sources. In the case of 57Co standardisation, the software coincidence counting system was applied for the evaluation of optimal setting of coincidence parameters. The results obtained by software coincidence counting system were compared with those obtained by the conventional coincidence method.