A Comprehensive Study of Natural Gamma Radioactivity Levels and Associated Dose Rates from Surface Soils in Cyprus
A survey was carried out to determine activity concentration levels and associated dose rates from the naturally occurring radionuclides Th-232, U-238, and K-40, in the various geological formations appearing throughout the geographically accessible area of Cyprus, by means of high-resolution gamma-ray spectrometry. A total number of 115 representative soil samples were collected from all over the bedrock surface of the island, based on the different lithological units of the study area, sieved through a fine mesh, sealed in 1000-mL plastic Marinelli beakers, and measured in the laboratory with respect to their gamma radioactivity for a counting time of 18 hours each. From the measured spectra, activity concentrations were determined for Th-232 (range from 1.0x10^-2 to 39.8 Bq/kg), U-238 (from 1.0x10^-2 to 39.3 Bq/kg) and K-40 (from 4.0x10^-2 to 565.8 Bq/kg). Gamma absorbed dose rates in air outdoors were calculated to be in the range of 1.1x10^-2 - 51.3 nGy/h, depending on the geological features, with an overall mean value of 8.7 nGy/h and a standard deviation of 8.4 nGy/h. This value is by a factor of about 7 below the corresponding population-weighted world-averaged value of 60 nGy/h reported by UNSCEAR (2000), and one of the lowest that has been reported from similar investigations worldwide. Assuming a 20% occupancy factor, the corresponding effective dose rates outdoors equivalent to the population were calculated to be between 1.3x10^-2 and 62.9 micro Sv/y, with an arithmetic mean value of 10.7 micro Sv/y and a standard deviation of 10.3 micro Sv/y.