Groundshine dose-rate conversion factors of soil contaminated to different depths

For assessment of external doses from the ground contaminated with radionuclides, the dose-rate conversion factors (DCFs) prescribed in FGR (Federal Guidance Report) 12 have been used. Recently, significant changes were made by International Commission on Radiological Protection in dosimetric models and parameters, which include use of Reference Phantoms and revised tissue-weighting factors, as well as the updated decay data of radionuclides. The DCFs for effective and equivalent doses due to groundshine from contaminated soil were re-calculated by taking the changes into account. In this study, the DCFs for effective and equivalent doses were calculated for depths of 1, 5 and 15 cm and for infinite deposition. Doses to the Reference Phantoms were calculated by Monte Carlo simulations with the MCNPX 2.7.0 radiation transport code for 26 mono-energy photons between 0.01 and 10 MeV. Transport calculations were performed for the source volume within the converging of distances and depths practically contributing to the dose rates, which were determined by a simple model. With the resulting doses, empirical response functions were constructed as a function of photon energy. The DCFs for the radionuclides considered important were evaluated by combining the photon emission data of the radionuclide and the response functions. Finally, the contributions of accompanied beta particles to the skin equivalent doses and the effective doses were calculated separately and added to the DCFs. For radionuclides considered in this study, the new DCFs for the different depths agreed within 10 % with the data in FGR12. (authors)