Variation in the radon concentrations and outdoor gamma radiation levels in relation to different geological formations in the thermal regions of Bursa, Turkey

Spring waters used as spas and their region may contain significant amounts of natural radionuclides. The main sources of exposure are the inhalation of radon and its decay products released from the water and soil and terrestrial gamma-radiation. In order to evaluate the potential risk of thermal regions in Bursa, located in the impact area of the NAF (North Anatolian Fault), radon and thoron concentrations in soil gas, radon concentrations in thermal waters and outdoor gamma radiation levels were measured in thermal regions that have different geological formations. The radon and thoron concentrations in soil-gas were found to vary from 2272 +/- 121 to 245196 +/- 3455 Bq m(-3) and from 999 +/- 218 to 178 848 +/- 17 742 Bq m(-3), respectively. The radon concentrations in thermal waters ranged from 0.99 +/- 0.21 to 226.74 +/- 2.51 Bq l(-1) in the rainy season and from 0.26 +/- 0.10 to 178.03 +/- 12.86 Bq l(-1) in the dry season. The measured outdoor gamma radiation levels varied from 38 to 180 nGy h(-1). The gamma dose rates were found to be strong positively correlating with the radon and thoron concentrations in soil-gas. The radon and outdoor gamma radiation levels were observed to be a function of the geological formations of the area