Accuracy associated with the activity determination by in situ gamma spectrometry of naturally occurring radionuclides in soils

摘要

In situ gamma spectrometry (ISGS) is a technique mainly focused on the determination of man-made radionuclides deposited on soils. It is widely used for the radioactive characterization of soils in which there has been an incorporation of such radionuclides; especially Cs-137. Its use for the activity determination of naturally occurring radionuclides in soils has been more limited, and the accuracy associated with those measurements has yet to be treated extensively. There are numerous factors affecting the accuracy of the activity determination of naturally occurring radionuclides, such as the assumed soil geometry, the soil's geological and mineral composition, its moisture content, etc. The present work studies the accuracy associated with the ISGS determination of the activity concentrations of natural radionuclides in soils using a portable HPGe detector. For K-40 and Th-232 activity determinations, the uncertainties associated with ISGS are generally of the order of 15%. However, Ra-226 activity determined from its daughters Pb-214 and Bi-214 can be significantly overestimated when there is a major presence of Rn-222 in the air around the detector. Finally, absorbed dose rate in air values were calculated from the naturally occurring radionuclide concentration in soils. The results showed good correspondence between the values obtained from ISGS and those obtained from laboratory determinations with the same soils. (C) 2016 Elsevier Ltd. All rights reserved.