The absolute determination of activity by the efficiency extrapolation method

Abstract

As an agent for the Commonwealth Scientific and Industrial Research Organisation, the Australian Atomic Energy Commission is responsible for the maintenance of the Australian standard of activity. The standard comprises activity measurement procedures involving the operation of 4 pi β-γ coincidence counting equipment. The coincidence method requires the application of correction factors which depend on detection efficiency such as arise for complex decay schemes and internal conversion. These corrections approach unity as the detection efficiency in the β-channel approaches 100 per cent. By performing activity determinations for a range of β detection efficiencies an 'efficiency extrapolation' analysis can be applied which eliminates the need to determine the absolute detection efficiency for each channel.