staff exposure rate in mahallat hot spring region

background: high level radiation areas have been recognized on various parts of the earth. mahallat hot spring region is one of these areas. study of exposure in these areas can be helpful in investigating the effects of ionizing radiation. internal and external exposure to the staff was studied. materials and methods: used materials and instruments include: rss-112 ionizing chamber for environmental gamma rays measurement, pure germanium detector for measuring radioactive elements in the ground, liquid scintillation counter for measuring 222rn gas concentration in water samples, bubbler chamber and locus cells for 226ra concentration measurements as emanation method and alfa guard detector for 222rn concentration measurements. results: considering stay period of the studied groups in indoor and outdoor environment, calculated annual external effective dose for staff has been 514.8 ± 22.7 μsv. annual internal effective doses for staff in outdoor and indoor environment has been 21.1 msv. annual internal effective dose for staff due to drinking water has been 32 μsv. conclusion: measurements showed that more than 90% of the received dose in the studied groups was due to inhalation of radon gas. external and internal effective dose for the staff was 21.6 msv. considering these results mahallat hot spring region is a high level natural radiation area (hlnra). iran. j. radiat. res., 2008 6 (1): 13-18