Calculation of dose conversion coefficients for the radionuclides in soil using the Monte Carlo method

In determining the radiation background of a region, it is important to carry out environmental radioactivity measurements in soil, water and air, to determine their contribution to the dose rate in air. This study aims to determine the dose conversion coefficients (in {nGy/h}/{Bq/kg}) that are used to convert radionuclide activity concentration in soil (in Bq/kg) to dose rate in air (in nGy/h) using the Monte Carlo method. An isotropic source which emits monoenergetic photons is assumed to be uniformly distributed in soil. The doses released by photons in organs and tissues of a mathematical phantom are determined by the Monte Carlo package MCNP. The organ doses are then used, together with radiation weighting factors and organ weighting factors, to obtain effective doses for the energy range of 100 keV-3 MeV, which in turn are used to determine the dose rates in air per unit of specific activity.