A comprehensive study of natural gamma radioactivity levels and associated dose rates from surface soils in cyprus

Abstract

A survey was carried out to determine activity concentration levels and associated dose rates from the naturally occurring radionuclides 232Th, 238U and 40K, 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 232Th (range from 1.0 x 10(-2) to 39.8 Bq kg(-1)), 238U (from 1.0 x 10(-2) to 39.3 Bq kg(-1)) and (40)K (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 microSv y(-1), with an arithmetic mean value of 10.7 microSv y(-1) and a standard deviation of 10.3 microSv y(-1).