The determination of depth distributions of radioactive cesium in the ground using in situ gamma-ray spectrometry

In situ measurements with specific algorithms and hardware, which means multiple photopeaks, peak-to-valley, and collimation method, have been using to estimate the depth distribution of nuclides in the ground. In this study, a simple method to estimate the depth distributions of nuclides was developed by calculating the individual dose rate of detected gamma nuclides at 1 m above the ground. The dose rate spectroscopy was then used to previously determine the individual dose rate of ¹³⁷Cs from the measured energy spectrum using a portable HPGe detector. In addition, theoretical individual dose rates of ¹³⁷Cs at 1 m above the ground were calculated by assuming several depth distributions of ¹³⁷Cs in the ground. The real depth distribution of ¹³⁷Cs was determined from the comparison between them. Its radioactivity in the ground was then calculated by applying the dose conversion factor in the unit of nGy/h/Bq/m² in the condition of the determined depth distribution.