External Doses to Terrestrial Gamma Rays on the Snow Cover

The external doses due to terrestrial gamma rays in the presence of snow cover were investigated using Monte Carlo calculations. The attenuation of air kerma by snow cover was determined for snow water equivalents of 0-50 cm at heights up to 250 m. The difference in attenuation was discussed for the main natural gamma ray sources of the 238 U series, the 232 Th series and 40 K. It was shown that the major part of terrestrial gamma rays when there is snow cover come from the bottom direction. Organ doses from terrestrial gamma rays on the snow cover were calculated using anthropomorphic phantoms. The effective dose equivalent per air kerma on the snow cover at a water equivalent of 30 cm was found to be smaller than that on bare ground by 5-20%