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 of Cyprus, by means of high-resolution gamma ray spectrometry. A total 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 gamma radioactivity for a counting time of 18-h each. From the measured spectra, activity concentrations were determined for Th-232 (range from 1.0 X 10(-2) to 39.8 Bq kg(-1)), U-238 (from 1.0 X 10(-2) to 39.3 gq kg(-1)) and K-40 (from 4.0 x 10(-2) to 565.8 Bq kg(-1)). Gamma absorbed dose rates in air outdoors were calculated to be in the range from 1.1 X 10(-2) to 51.3 nGy h(-1), depending on the geological features, with an overall mean value of 8.7 nGy h(-1) and a standard deviation of 8.4 nGy h(-1). This value is by a factor of about seven below the corresponding population-weighted world-averaged value of 60 nGy h(-1) 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 1.3 x 10(-2) and 62.9 muSv y(-1), with an arithmetic mean value of 10.7 muSv y(-1) and a standard deviation of 10.3 pSv y(-1).