Knowledge of natural radioactivity in man and his environment is important since naturally occurring radionuclides are the major source of radiation exposure to man. One of the main sources of public exposure from natural radioactivity is radium and radon and its short lived decay products. This radio nuclides are produced from the decay of uranium. Drinking water containing 226Ra, fifth member of the 238U series, is dangerous for people health, because this element deposits in bones and caused to bone cancer. Also, radon the decay product of 226Ra can enter to the body via respiring, drinking and eating. Radon and its decay products emit alpha particles that lead to increase the absorbed dose in respiratory and digestion systems, which may cause cancers. The aim of this study is focused on determining the concentration of mentioned radionuclides in the water resources of the Ramsar, Sadatshar and Javaherdeh regions, in north Iran .In this study radon and radium concentrations of the 120 water samples of this regions have been measured by PRASSI system. 11 samples have radon concentration higher than 11 Bq/L as normal level. Also, 226Ra in 53 samples have concentration higher than 0.185 Bq/L as normal level for radium-226. Similarly, the annual effective dose in stomach and lung per person has been evaluated in this research. According to the advice of WHO and EU Council, radon induced the total annual effective dose greater than 0.1 mSv/y in 2 sample and in 12 samples the annual effective dose is induced by radium greater than 0.1 mSv/y.

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