Assessment of Natural Radioactivity Levels in Some Environmental Rock Samples from Taiz, Yemen

Abstract

There is increasing interest in the last years to estimate the natural radioactivity in the surrounding environment. This study focused on the evaluation of naturally occurring radionuclides Ra-226, Th-232 and K-40 and the associated hazard indices in twenty-five rock samples from Taiz region, Yemen. The measurements are carried out by gamma ray spectroscopy technique using HPGe detector with special designed shield. Also, the radon exhalation rate and effective radium content are estimated in some samples by the sealed cup technique using the CR-39 detector. Furthermore, the X-ray fluorescence technique was used for determining the strategic elements that may be present in the selected samples. The X-ray analysis showed that there are considerable concentrations of some strategic elements such as Fe, Al, Zr and Ti have been observed. The mean activity concentrations of 226Ra, 232Th and 40K were found to be 65.58±1.38, 82.93±0.93 and 976.40± 6.11 Bq kg-1 respectively. These values exceed the maximum international limits. The mean values of radium equivalent, external hazard index, internal hazard index and radiation level index are estimated and found to be 259.35 Bq kg-1, 0.70, 0.88, and 0.96 respectively. The mean values of the absorbed dose rate, annual effective dose equivalent, annual gonadal dose equivalent and the excess lifetime cancer risk are calculated and found to be 121.10 nGy h-1, 0.15 mSv y-1, 0.86 mSv y-1 and 0.52 × 10-3 receptively. Also, the mean values of radon exhalation rate (areal and mass) were found to be 4.20±0.010Bq m-2 h-1 and 120±0.29×10-3Bq kg-1 h-1respectively. Furthermore, the calculated values of the effective radium content lie in the range from 3.85±0.021to 76.65±0.095Bq kg-1 with a mean value of 15.57±0.039Bq kg-1 whilethe results of emanation power lie in the range from 0.09±0.017 to 0.33±0.030 with a mean value of 0.15±0.024. Based on these data, the obtained values can be considered as a baseline for drawing a radiological map of Taiz region in Yemen and for any future studies. .