Total effective dose equivalent assessment after exposure to high-level natural radiation using the RESRAD code

The current work reports the activity concentrations of several natural radionuclides ((226)Ra, (232)Th, and (40)K) in Khak-Sefid area of Ramsar, Iran. An evaluation of total effective dose equivalent (TEDE) from exposure to high-level natural radiations is also presented. Soil samples were analyzed using a high-purity germanium detector with 80 % relative efficiency. The TEDE was calculated on a land area of 40,000 m(2) with 1.5-m thickness of contaminated zone for the member of three critical groups of farmer, construction worker, and resident using Residual Radioactive Material Guidelines (RESRAD) modeling program. It was found that the mean activity concentrations (in Bq/kg) were 23,118 ± 468, 25.8 ± 2.3, and 402.6 ± 16.5 for (226)Ra, (232)Th, and (40)K, respectively. The maximum calculated TEDE during 1,000 years was 107.1 mSv/year at year 90, 92.42 mSv/year at year 88, and 22.09 mSv/year at year 46 for farmer, resident, and construction worker scenarios, respectively. The maximum TEDE in farmer scenario can be reduced to the level below the dose limit of 1 mSv/year which is safe for public health using soil cover with thickness of 50 cm or more on the contaminated zone. According to RESRAD prediction, the TEDE received by individuals for all exposure scenarios considerably exceed the set dose limit, and it is mainly due to (226)Ra.