226Ra 232Th and 40K concentrations in igneous rocks from eastern desert, Egypt and its radiological implications

By applying high-resolution gamma-ray spectroscopic system, the various radionuclides of the granite samples have been identified quantitatively based on the characteristic spectral peaks. The radionuclides Ra-226, Th-232 and K-40 concentrations measured as well as radiological parameters, for 49 granite samples were calculated. This subject is important in environmental radiological protection, since granites are widely used as building and ornamental stones. The variation in concentration of radionuclides for the Um Taghir area can be classified into two regions of low and high natural radioactivity. In old granite, the measured x-ray spectra, activity concentrations were determined for Ra-226 (from 2.9 +/- 1 to 31.8 +/- 6 Bq kg(-1)), Th-232 (range from 1.4 +/- 1 to 14.9 +/- 4 Bq kg(-1)) and K-40 (from 132 +/- 11 to 2080 +/- 46 Bq kg(-1)), in younger granite Ra-226 (from 8.9 +/- 3 to 9087 +/- 95 Bq kg(-1)), Th-232 (range from 9.8 +/- 3 to 3834 +/- 62 Bq kg(-1)) and K-40 (from 471 +/- 22 to 10230 +/- 101 Bq kg(-1)). In Wadi Karim area these values were (14.0 +/- 4-227.0 +/- 15, 10.5 +/- 3-183.0 +/- 14 and 2299 +/- 48-7356 +/- 86 Bq kg(-1)). The highest values of Ra-226, Th-232 and K-40 concentration (9087 +/- 95, 3834 +/- 62 and 10230 +/- 101 Bq kg(-1), respectively) were observed in anomalies samples at Um Taghir region. Radium-equivalent activities (Ra-eq) in addition to the internal hazard index (H-in) have also been determined. In Um Taghir samples Ra-eq varies between 15 and 625 Bq kg(-1) (old granite), 144-13 982 Bq kg(-1) (younger granite) which exceeds the permitted value (370 Bq kg(-1)) and hazard index (H-in) (0.05-1.74), (0.65-62.34) which is higher than 1, the corresponding values in Wadi Karim samples were 206-685 Bq kg(-1) and from 0.59 to 2.46, respectively. The total absorbed dose rates in air calculated from the concentrations of the three radionuclides ranged from 8 to 6187 nGy h(-1), and the external annual effective dose rate of the areas were determined to be between 0.04 and 30.37 mSv y(-1). This study provides a baseline map of radioactivity background levels in the Egyptian environment and will be used as reference information to assess any changes in the radioactive background level due to geological processes. (c) 2006 Elsevier Ltd. All fights reserved.