EFFECTIVE DOSE DUE TO TERRESTRIAL GAMMA RADIATION ESTIMATED IN SOUTHERN VIETNAM BY CAR-BORNE SURVEY TECHNIQUE.

Absorbed dose rates in air from natural radionuclides were measured by a car-borne survey in southern Vietnam. The mean absorbed dose rate in air for southern Vietnam, which consists of the south-east region and the Mekong River Delta region, was 64 ± 18 nGy h-1, while rates for the two regions were 61 ± 17 and 66 ± 19 nGy h-1, respectively. These dose rates were respectively 1.2, 2.1 and 0.9 times the measured values that were calculated on the basis of activity concentrations of soil samples in a previous study. It was considered that measured dose rate in the south-east region was influenced by the presence of artificial structures such as high-rise buildings and roads. The effective dose due to terrestrial gamma radiation for southern Vietnam was calculated to be 0.55 mSv y-1 which is 1.2 times higher than the world-wide average of 0.48 mSv y-1.