Terrestrial outdoor exposures in the south-west Caspian region

Natural radionuclides (40)K, (232)Th and (238)U present in soil and anthropogenic (137)Cs a fission product released to the environment mainly through atmospheric testing of nuclear arms and accidents in nuclear installations are the major contributors to terrestrial outdoor exposures. As part of a comprehensive study of environmental radioactivity in the south Caspian region, soil inventories of these radionuclides have been measured in more than 50 locations throughout Guilan, a northern province of Iran with the highest population density. In the case of natural radionuclides, outdoor absorbed dose rates in air have been inferred from concentrations of radionuclides in soil on the basis of which annual effective dose values have been estimated using the method described in UNSCEAR 2000. Calculation of (137)Cs contribution to dose has been performed by considering its soil inventory profiles and associated numerically estimated photon fluxes at 1 m above the ground. Maps representing the contribution of natural and anthropogenic radionuclides to annual effective dose in the study area have been produced using relevant geostatistical technique. Combined annual effective dose equivalent ranges from 33.1 ± 4.9 to 91.9 ± 16.5 μSv · y(-1) with a mean value of 64.7 ± 15.2 μSv · y(-1).