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 e fficiency of gamma-spectrometry measurement systems. The technique use s the relationship between total- and full energy efficiency of a Ge-d etector. First, the full energy peak efficiency of a closed point sour ce standard centred at the face of the detector is measured at differe nt energies with known activities of nuclides. As this calibration rec ords all the required characteristics of the detector, other experimen tal or theoretical views are not necessary. The experimental part is t herefore complete and all other factors are calculated from the effici ency calibration of the point source and detector with a recently deve loped 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 det ermining the total efficiency. This MC-simulation calculates all the o ther factors required, namely: the sum of the path lengths of the phot ons 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 ef ficiency of the point and volume sources.