Monte Carlo calculation of gamma radiation field due to precipitation washout of radon daughters from the atmosphere to the ground surface

A one-dimensional Monte Carlo transport code for the propagation of gamma radiation in two medium geometry is developed to evaluate properties of the radiation field due to the washout of short-lived radon daughters from the atmosphere to the ground surface by precipitation. To assess the validity of the results provided by this code, the calcuations on the radiation field from uniformly distributed terrestrial 238U source in the natural environment are compared with numerical calculations of other investigators. The comparison shows satisfactory agreement between them. The calculated data are presented on the height distribution and on the energy and angular distribution of flux density and exposure rate from an infinite plane isotopic RaB and RaC sources with known abundances on the ground-air interface. (author)