Determination of activity concentration of U-238 and Th-232 series radionuclides in soil using a gamma-ray spectrometer in singles and coincidence modes

摘要

Traditionally, activity concentrations of naturally occurring radioactive materials (NORMs) are measured using a gamma-ray spectrometer with a single detector shielded with lead. In this measurement, a gamma-ray spectrometer comprising an array of four LaBr3:Ce detectors without shielding was used. This spectrometer allowed for measurement in singles and coincidence (gamma-gamma) modes. In addition to using the coincidence method, a novel method of background reduction by using the photon time-of-flight was utilized. Activity concentration of U-238 and Th-232 series radionuclides in soil reference (IAEA-375) and beach-sand (Bs) were measured in singles and coincidence modes. In coincidence mode, the minimum detectable activities (MDAs) were lower by a factor of 8-36 than for singles mode. Activity concentration of U-238 and Th-232 series in soil material (IAEA-375) were determined in coincidence mode while it was below MDA in singles mode. The results correlate with the certified values to within the uncertainty although the uncertainties were high because of low statistics.