Determination of full energy peak efficiency for cylindrical volume sources by the use of a point source standard in gamma-spectrometry

A new method has been developed for calculating the full energy peak efficiency of gamma-spectrometry measurement systems. The technique uses the relationship between total- and full energy efficiency of a Ge-detector. First, the full energy peak efficiency of a closed point source standard centred at the face of the detector is measured at different energies with known activities of nuclides. As this calibration records all the required characteristics of the detector, other experimental or theoretical views are not necessary. The experimental part is therefore complete and all other factors are calculated from the efficiency calibration of the point source and detector with a recently developed Monte Carlo simulation [G. Haase et al., Nucl. Instr. and Meth. A 329 (1993) 483, and Nucl. Instr. and Meth. A 336 (1993) 206] for determining the total efficiency. This MC-simulation calculates all the other factors required, namely: the sum of the path lengths of the photons in the volume source and the detector, the sum of the path lengths of the photons in the detector for the point source, the value of the self-attenuation of the photons in the volume source and the total efficiency of the point and volume sources.