OUTDOOR GAMMA RADIATION MEASURMENT IN ORDER TO ESTIMATE THE ANNUAL EFFECTIVE DOSE an‎d EXCESS LIFETIME CANCER RISK FOR RESIDENTS OF TEHRAN, IRAN

Introduction: Gamma ray radiation can cause ionization and harmful effects on human health due to its high levels of energy. However, contrary to popular belief, natural sources of gamma radiation are far greater in number than artificial sources. This study aims to determine the environmental gamma dose rate and the zoning map of Tehran, and estimate the annual effective dose and the excess risk of cancer in Tehran. Materials and methods: This study is descriptive and cross-sectional. In it, the researchers measured the gamma radiation rate using a Geiger Muller detector at 50 outdoor stations in Tehran during the winter and the spring of 2016. The data was zoned using Arc GIS 10.3. Results: The average background environmental gamma dose rate in Tehran was obtained at 605.54 nsv/h. There is a statistically significant difference between radiation in winter and in spring (P <0.05). The annual effective dose for the inhabitants of Tehran and the cancer risk were estimated to be 0.74 mSv and 2.29×10-3 respectively. Conclusions: The annual effective dose and cancer risk in the lifetime of a Tehran city resident due to background gamma radiation were higher than the global average. Epidemiologic studies are recommended to assess the likely prevalence of chronic diseases associated with natural radiation among the residents of Tehran.