Optimization of γ-Spectrometry Measurements of Radionuclides of Natural Thorium-232 and Uranium-238 Series

Abstract The nuclear-physical properties of radionuclides of natural 232 Th and 238 U series differ significantly; therefore, the problem of selecting particular γ-lines for calculations arises in direct γ-spectrometry measurements in assessing the absolute activities of the parent radionuclides of these series. In the present study, we develop an approach yielding a reliable value of the specific activity of 232 Th and 238 U by a single measurement of a sample with the smallest deviation from the true value. We used a bottom sediment sample, taken during the 66th cruise of the Akademik Mstislav Keldysh research vessel in the Kara Sea (station coordinates: 72°30.4' N, 80°20.4' E; depth 14 m), as a model sample. When processing the results, only those lines were selected from the entire set of lines belonging to the 232 Th natural series, the quantum yield of which exceeded 2% (taking into account branching). When analyzing the natural 238 U series, we selected lines that were free from interference with nuclides of the 232 Th series and with the quantum yield above 3%.