The 222Rn radioisotope with 3.8 days decay half-life is produced from 238U natural series and the 220Rn radioisotope with 55 sec decay half-life from 232Th natural series. Radon can enter to the body via respiring, drinking and eating. Alpha and other radiation which are emitted by radon and its daughters increase the absorbed dose in respiratory and digestion systems. Nearly 50% of annually radiation dose absorption of human is due to radon which is one of the main cancers cause at respiratory and digestion systems. In this work, radon and radium concentration in the 8 springs, flume and rivers water sources of Kelardasht-Kalenov region have been measured with PRASSI system. Kelardasht is a city in the north of Iran between the Elburz Mountains and the Caspian Sea. The results show 6 samples have radon concentration gather than 10 Bq/l, also 2 samples have high radium concentration. So, for improvement of the social health level, it would be better to use the low radon level water supplies, and reduce the radon in the drinkable water before using by people.

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