On the applicability of the effective solid angle concept in activity determination of large cylindrical sources

Abstract

We known activities of two large cylindrical γ-sources (a mixture of radionuclides in solution, and a geological sample) are measured using a semiempirical method for calculating photon detection efficiencies (e p ) of Ge-detectors via effective solid angles $$\overline {(\Omega )} $$ , in order to analyse the feasibility and the accuracy of the method. It is applied here under conditions not favourable to the method itself, which are however quite common in practice: (1) HPGe detector supplied only with standard detector specification and performance data, and (2) large source just above the detector end-cap. The impact of the probable range of uncertainties in knowledge of the detector and source geometrical parameters on the calculated efficiencies is considered. The fact that the crystal of the detector used is not coaxial with the end-cap, discovered by making X-ray radiographs, is of a special concern with respect to the applicability of the method under such conditions. Therefore, the method for the calculations of Ω is extended to cases of parallel but not coincident axes of the cylindrical sources and detectors. True coincidence effects, which introduce typically 5% errors for the counting geometry used, are not dealt with.