Method-sensitivity of in-situ γ spectrometry to determine the depth-distribution of anthropogenic radionuclides in soil

The main limitation of in-situ γ spectrometry lies in determining the depth-distribution of the anthropogenic radionuclide in soil. Many researchers have developed methods and models for deducing the depth-distribution information from spectrum measured in-situ. Until now, such methods were studied and established as “Multiple photopeak method”, “Collimation method” and “Peak-to-valley ratio method”. This paper presents the comparative theoretical study on the method-sensitivity. The Multiple photopeak, Collimation and Peak-to-valley ratio methods were studied at energies of 244keV and 1408keV γ-rays of 152Eu, 662keV γ-ray of 137Cs, and 662keV γ-ray of 137Cs, respectively, and the In-situ object counting system was employed in Collimation method. For all methods the exponential function was adopted to depict the depth-profile of anthropogenic radionuclide. Results indicate that the sequence of method-sensitivity from the maximum to the minimum was as following: Peak-to-valley ratio method, Multiple photopeak method, and Collimation method, and the sensitivity of Collimation method was far less than Multiple photopeak method.