Natural radioactivity levels and estimation of radiation exposure in agricultural soils from Skopje city region

Abstract

The aim of this study was to determine the activity concentrations of naturally occurring radioiso-topes 226Ra, 232Th and 40K in 14 soil samples collected in the Skopje city surroundings, and to calculate the corresponding absorbed gamma dose rates. The radionuclides were measured applying a high purity Ge detector gamma-ray spectrometer with relative efficiency of 30 % at 1.33 MeV. The activity concen-trations found in 14 soil samples varied in the range of 24.1-41.9 Bq kg-1 for 226Ra, 38.5-52.2 Bq kg-1 for 232Th and 502-707 Bq kg-1 for 40K. The mean radium equivalent (Raeq), for the area under investigation, was 143 ± 16 Bq kg-1, while the outdoor radiation hazard index (Hex) was 0.39. The total absorbed dose rate due to the three primordial radionuclides investigated lay in the range of 55.3-79.0 nGy h-1 with a mean value of 68.1 ± 7.7 nGy h-1, yielding a total annual effective dose of (83.5 ± 9.5) μSv y-1. The as-sessed radiological factors were lower than the recommended values, indicating a low radiological health risk for the population living and working in the investigated area. The activity concentrations of radionu-clides in soil samples were compared to the international values reported by United Nations Scientific Committee on the Effects of Atomic Radiation and previous studies on geographically close areas and some worldwide regions.