Public exposure to natural radiation sources (Ramsar Case Study)

Introduction: Human beings are naturally exposed to ionizing radiation in any environment. There are two main contributors to radiation exposures from natural sources: cosmic rays, Cosmo genic radionuclides, and radioactive nuclides that originated in the earth's crust. According to the latest data provided by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), the estimated worldwide average annual exposure to natural radiation sources is 2.4 mSv, and the most exposures are in the range of 1–13 mSv/a. There are several small areas throughout the world where people are exposed to natural radiation sources that are in excess of those considered "normal background”. However, there are no specific criteria in this regards, these areas are referred to as "High Natural Radiation (HNRA)" areas. Ramsar is one of these areas. The natural radioactivity of Ramsar is mainly due to the presence of Ra-226 along with its daughters. The aim of this study was to determine the internal and external exposures from natural radiation sources in Ramsar, and to estimate the total annual effective dose for the people in Ramsar.   Materials and Methods: In this research, the all radiation sources and exposure pathways of people living in Ramsar were investigated. The concentration of 226Ra was measured by alpha spectrometry and radon emanation in different samples including foods and drinking water, and the internal dose was estimated. In addition, the annual effective dose of exposure to gamma rays and the annual effective dose due to inhalation of radon gas were calculated for residents.   Results: The mean annual effective dose due to exposure to indoor gamma rays in Ramsar was 0.66 mSv, the range was 0.3 to 48 mSv, the mean annual effective dose due to exposure to outdoor gamma rays was 0.86 mSv, and the minimum was 0.1 mSv. The mean annual effective dose of internal exposure to radon gas was 10.3 mSv and its range was from 0.9 to 232 mSv. The mean annual effective dose due to ingestion of 226Ra was found 10 µSv and its range was 1 to 81 μSv.   Conclusion: Based on the results of this study, the public annual effective dose of Ramsar from exposure to natural radiation sources was 1.25 to 281 mSv, with a mean value of 12 mSv. The results of this study show that the mean value (12 mSv) is approximately 5 times greater than the worldwide mean annual exposure to natural radiation sources reported by the UNSCAER (2.4 mSv). The results obtained could be used in determining the reference levels for controlling the exposure of people and in taking preventive measures to reduce the radiation exposure of the residents. In addition, the results of this research could be useful    in the study of the effect of radiation on the public health.