Correction factors to account for minor sample height variations in gamma-ray spectrometry

It often happens in gamma-ray spectrometry measurements that there is less sample material than required for the given measuring geometry. One approach to this problem is to stick to the original geometry, though a correction factor is to be introduced to account for the difference in the height of the sample material. This correction factor Ch is expressed as the ratio of spectrometer efficiency for the nominal sample height ε(h0) to that obtained for the actual height ε(h).The author determined the correction factor Ch for several radiation energies E, 81.0, 356.0, 661.7 and 1173.2 keV. Two measurement geometries were considered: a Marinelli beaker 710 cm3 in volume, and a cylindrical sample 31.5 mm in height. The correction factors were obtained experimentally and by Monte Carlo simulation method for h falling within the range h0±8 mm. Ch values obtained by these two methods are consistent. For E⩾356 keV, Ch value almost does not depend on energy. Ch value varies linearly with dh. For Marinelli beaker for E⩾356 keV, the correction is 0.9% (1.0% for E=81 keV) for each millimeter of sample height change; for a cylindrical geometry the correction is 1.5% (1.7%). Monte Carlo method was further used to compute Ch values for several other cylindrical geometries. The lower the nominal height of the cylindrical samples, the more sensitive the method to sample height variations. The knowledge of the value Ch enables us to estimate the uncertainty of the measurements, associated with the sample height uncertainty.