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 radioisotopes 226Ra, 232Th and 40K in 14 soil samples collected in the Skopje city surrounding, 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 concentrations found in 14 soil samples varied in the range 24.1-41.9 Bq kg-1for 226Ra, 38.5-52.2 Bq kg-1 for 232Th, and 502-707 Bq kg-1 for40K. 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 three primordial radionuclides investigated lay in the range 55.3 - 79.0 nGy h-1 with 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 assessed radiological factors were lower than the recommended values, indicating low radiological health risk for the population living and working in the investigated area. The activity concentrations of radionuclides 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.