A COMPREHENSIVE STUDY OF NATURAL GAMMA RADIOACTIVITY LEVELS AND ASSOCIATED DOSE RATES FROM SURFACE SOILS IN CYPRUS

摘要

A survey was carried out to determine activity concentration levels and associated dose rates from the naturally occurring radionuclides ~(232)Th, ~(238)U and ~(40)K, 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 ~(232)Th (range from 1.0×10~(-2) to 39.8 Bq kg~(-1)), ~(238)U (from 1.0×10~(-2) to 39.3 Bq kg~(-1)) and ~(40)K (from 4.0×10~(-2) to 565.8 Bq kg~(-1)). Gamma absorbed dose rates in air outdoors were calculated to be in the range from 1.1×10~(-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 1.3×10~(-2) and 62.9 μSv y~(-1), with an arithmetic mean value of 10.7 μSv y~(-1) and a standard deviation of 10.3 μSv y~(-1).