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Abstract: The first radon soil gas survey in Serbia, using passive detectors (SSNTD, CR-39), was carried out in June 2005 at field sites in Niška Banja town. The aim of the survey was to identify risk zones characterised by high levels of this radioactive gas. Radon measurements were made at the depth of 50cm, in the ground according to a systematic grid pattern. Furthermore, at all 48 measurement points, the surface gamma dose rates in the air was also measured at the same locations and soil samples were collected for gamma spectrometric analysis for the radionuclides 226Ra, 228Th and 40K. Radon concentrations were found to range from 1270 to with an average of and a median value of . The geometrical mean value and geometrical standard deviation were calculated as and , respectively. Gamma dose rate varies from 92 to , with an average of . The radium content in collected soil samples ranges from 24 to with an average of . High correlations () between soil gas radon concentration, gamma dose rate and 226Ra content in soil were found for each pair. The distribution of radon concentrations in soil gas shows bimodal shape. [Copyright &y& Elsevier]

Based on results of fieldwork in the Balkan Region of Serbia from 2005 to 2007, soil gas radon and thoron concentrations as well as gamma dose rates were measured. Campaigns were conducted in two different geological regions: Niska Banja, considered a high natural radiation area, and Obrenovac around the TentB Thermal Power Plant (TPP), a low natural radiation area. Radon and thoron gas measurements were made by using two types of Japanese passive radon/thoron detectors, which included GPS data and gamma dose rates. The concentrations of soil radon gas in Niska Banja ranged from 1.8 to 161.1 kBq m(-3), whereas the concentrations for soil thoron gas ranged from 0.9 to 23.5 kBq m(-3). The gamma dose rates varied from 70 to 320 nGy h(-1). In the TentB area, radon concentration was found to range from 0.8 to 24.9 kBq m(-3) and thoron from 0.6 to 1.9 kBq m(-3). The gamma dose rate ranged from 90 to 130 nGy h(-1). In addition, the natural radioactivity of the soil was investigated at the low background area. The radium and thorium contents in collected soil samples ranged from 23 to 58 and 33 to 67 Bq kg(-1), respectively. As a result of correlation analyses between the measured values, the highest correlation coefficient (R > 0.95) was found for thorium in the soil and the thoron gas concentration.