Abstract
This study is aimed at the determination of the activity concentrations of naturally occuring and technically enhanced levels of radiation in 129 soil samples collected across the landscape of the State of Qatar. The State of Qatar is a peninsula with a total area of 11,437 km2 which lies over a geological formation comprising a sequence of limestone, dolomite, chalk, clay and gypsum. This work aims to establish the first baseline measurements for radioactivity concentration in the soil and (Saudi and Qatari) building materials collected from the Qatarian peninsula. Representative samples from various locations across the Qatarian peninsula have been collected and analysed in order to establish activity concentrations associated with the 235,8U and 232Th natural decay chains, the long-lived naturally occurring radionuclide 40K and the artificial man-made radionuclide 137Cs. The activity concentrations have been measured via high-resolution gamma-ray spectrometry using a hyper-pure germanium detector situated in a low-background environment with a copper inner-plated passive lead shield. A wide range of different gamma-ray energy transitions lines ranging from -100 keV up to 2.6 MeV associated with decays from the decay products of the 235,8U and 232Th decay chains have been analyzed separately to obtain more statistically significant overall results, under the assumption of secular equilibrium of the radionuclides within these samples. Using this method, a signficant improvement can be obtained in the statistical uncertainty of the derived activity concentrations. Details of the sample preparation and the gamma-ray spectroscopic analysis techniques are presented. Four radiological maps showing the activity concentrations of 226Ra, 232Th, 40K and 137Cs are presented. Five soil samples were found to be elevated in 226Ra concentrations. Two samples among the elevated samples were significantly above the average value. Notably, these samples were collected from an area contains an oil field (NW Dukhan). The weighted mean of the activity concentrations of 226Ra were found to be 201.93 ± 1. 54stat ± 12. 9syst. and 342 ± 1. 9stat ± 24. 9syst. Bq/kg respectively in these samples. The mean values of activity concentration of 226Ra, 232Th, and 40K for the full cohort of samples were found to be 17. 22 ± 1.55, 6.38 ± 0.26, and 169 ± 5 Bq/kg respectively. These values lie within the expected range relative to the world average values in soil samples of 30, 35 and 400 Bq/kg respectively. The mean value of activity concentration of 137Cs was also measured and found to be comparable with other published data. The mean value of gamma dose rate (D), the radium equivalent (Raeq), the external hazard index (Hex) and annual effective dose equivalent (AEDE) for the complete set of samples were all below the published maximal admissible values and indicate that the State of Qatar can be regarded as having normal levels of natural background radiation. The values of gamma dose rate obtained for samples no. X228 and 29-X228 were both found to be higher than the permissible value which is 51 nGy/h. They were 92. 82 ± 6.72 ±10. 23systematic and 160.27 ± 11.51 stat. ± 18.1syst. nGy/h respectively. The value of the radium equivalent (Raeq) in these two samples was found to be just below the permissible value of Raeq of 370 Bq/kg, which corresponds to an annual effective dose of 1 mSv. It was around 367.52 ± 26. 40Stat ± 41.51syst nGy/h. It can be concluded that the measured level of the natural radiation background in the present study show that the areas studied have normal levels of background radiation, with exception of these two areas. The measured level of natural radioactivity in the present study for the Saudi and Qatari building materials from the 20 investigated samples used in the State of Qatar is lower than other published data and lies within the world ranges for building materials of 50, 50 and 500 (Bq/kg) for 226Ra, 232Th and 40K, respectively. The gamma dose rate, the radium equivalent (Raeq), the external and internal hazard indices (Hex and Hint) and annual effective dose equivalent (AEDE) which were determined for each of the samples indicate that the State of Qatar can be regarded as having normal levels of natural background radiation.