New approach to study the response of portable gamma detector for   in-situ measurement of terrestrial gamma ray field
  A new approach to study the response of portable gamma detector to terrestrial gamma ray is proposed. This approach is based on two-stage Monte Carlo simulation. First, the probability distributions of the phase space coordinates of the events that are most likely to be detected are reconstructed at the phase space shell level. The phase space shell is a closed surface enclosing the detector. The detector response to events originating from the phase space shell is then studied. The full absorption spectra as well as the partial absorption spectra are obtained for natural radionuclides uniformly distributed in the ground. For validation, this method is applied to a HpGe portable detector previously studied. The previous study is based on a semi-empirical model. Good agreement is achieved when we compare the full energy peak efficiencies and the total in-situ spectra obtained by the two methods. As an application, the effective depth of the activity of the 137Cs artificial radionuclide in the soil is determined from the low-energy part of the total in-situ spectrum. 
Boubaker Askri
physics.ins-det