Dose-rate coefficients for external exposure to radionuclides uniformly distributed in soil to an infinite depth

Using a database on external exposures to environmental sources provided by the International Commission on Radiological Protection, monoenergetic and nuclide-specific dose-rate coefficients have been evaluated for volumetric sources with a uniform distribution to an effectively infinite depth in soil. Organ equivalent and effective dose rates for the public (newborns; 1-, 5-, 10-, and 15-year-old children; and adults), ambient dose equivalent rates, and air kerma free-in-air rates at 1 m above the ground were computed. This was performed using the weighted-integral method for monoenergetic photon and electron sources in an energy region of 10-2 to 8 MeV with 25 energy points to obtain the respective monoenergetic dose-rate coefficients. Then, based on these data, the dose-rate coefficients for 1252 radionuclides of 97 elements were evaluated. In those computations, the dose contribution from bremsstrahlung generated by electrons in the soil was also considered. In addition, dose-rate coefficients for the primordial radioactive decay chains of the thorium, uranium, and actinium series, as well as the decay of 137Cs with 137mBa in secular radioactive equilibrium, were obtained using the Bateman equation. For verification, the results of the effective dose rates for the 40K, 50V, thorium, and uranium series, as well as 137Cs/137mBa, were compared with those of previous studies and agreed within 10% for most cases. The results showed that the present dose-rate coefficients for radionuclides uniformly distributed to an infinite depth in soil were computed using appropriate procedures and can be used to assess external doses to the public, living on landfill soils containing naturally occurring radionuclides.