A national survey of natural radionuclides in soils and terrestrial radiation exposure in Iran

- Iran is host to world's most famous HLNRAs and this issue has dominated studying natural radioactivity in the country.
- The average activity concentration of Iran were found to be 457.7 Bq/kg for 40K, 24.3 Bq/kg for 226Ra and 25.8 Bq/kg for 232Th.
- The population-weighted average of calculated absorbed dose rate was 46.7 nGy h−1.
- The distribution of population with respect to total annual effective dose for Iran was presented.
- A map of natural radioactivity in soil Iran was provided.

In the past, some efforts have been made for measuring natural radioactivity and evaluating public exposure to natural radiation in certain areas of Iran especially in well-known High Level Natural Radiation Areas (HLNRA) in Ramsar and Mahallat. However, the information on radionuclide concentrations, and, consequently, terrestrial radiation exposure for many other areas are not available. There was therefore a need for a systematic and nation-wide survey. For this purpose, 979 soil samples from 31 provinces were collected. The activity concentrations of 40K, 226Ra and 232Th were measured by HPGe detector. The average activity concentrations for Iran were found to be 457.7 Bq/kg for 40K, 24.3 Bq/kg for 226Ra and 25.8 Bq/kg for 232Th. Results were compared with previous regional or provincial surveys. The population-weighted average outdoor and indoor annual effective dose due to external exposure to terrestrial sources of radiation are 0.06 mSv and 0.33 mSv, respectively. It was shown that there is a significant correlation between the activity concentrations of 232Th and 40K in soil. In addition, the results of chi square tests show normal and lognormal distributions cannot be considered for the frequency distributions of activity concentration of 232Th and 226 Ra while 40K has a normal distribution.