Determination of depth distributions of natural radionuclides with in situ gamma-ray spectrometry

To determine natural and artificial radio-nuclide concentrations in the ground in situ gamma-ray spectrometry method based on assumptions on the depth distribution of the radionuclides. In this paper two-slab geometries with different activities are assumed and two methods to derive information on the depth distribution of natural radionuclides from the measured spectra are examined. They use the distribution dependence of (1) the ratio of the primary and forward-scattered photons and (2) the attenuation of primary photons with different energies. Results of Monte Carlo simulations of the radiation transport and the detector response are compared with measurements on paved places and meadows with inhomogeneous vertical radionuclide distributions. Conditions are derived for which deviations from homogeneous distributions can be detected.