Self-attenuation correction in gamma-ray spectrometry analysis of geological samples using the transmission method

Laboratory gamma spectrometric analyses require correction for self-attenuation effect due to the interactions of the photons emitted by the sample and its own matrix. This issue becomes more important when samples of distinct densities and matrixes have to be measured. In this study, self-attenuation factors for efficiency correction of an HPGe detector, used for rock and soil radionuclide analyses, were calculated through gamma transmission measurements. These factors were calculated for 17 geological samples arranged in cylindrical recipients. For each sample, transmission measurements were accomplished for 17 energies ranging from 59 to 1409 keV, using three punctual sources, 152Eu, 133Ba and 241Am. The samples include several lithotypes (sandstone, siltstone, rhyolite and basalt), saprolite, soil, pure silica, pure calcium carbonate, a blend of carbonate and silica, and three IAEA reference materials for natural occurring radionuclide analysis, RG-K-1, IAEA-326 and IAEA-385. The densities varied from 0.5 to 2.2 g.cm-3. These data permitted a good fit with a theoretically deduced function that models the self-attenuation correction factor dependence on samples densities. The dependence on energy was empirically modeled. This function can be further used to correct the self-attenuation effect on gamma spectrometric analyses of other geological samples in the studied energy range. Some limitations of the model are discussed. (author)