Abstract
Igneous and sedimentary rocks contain an amount of natural radioactivity (NORM). U-238, Th-232 and their decay products, and K-40 are important sources of gamma-radiation. Knowledge of the radionuclide content of rocks is necessary to estimate the exposure of the population to the radiation. Many types of rocks are used in building and industries, thus the radiation detection is important, it provides a baseline map of levels of the radioactivity in the study region. The purpose of this study is to evaluate the activity concentrations of the natural radionuclides (U-238 (Ra-226), Th-232 and K-40) and the fallout nuclide (Cs-137) (if found) in thirty samples of igneous and sedimentary rocks of Al-Atawilah (Al-Baha). The samples were collected and prepared during 2018/2019, and analyzed with a good experimental instrument (High energy resolution γ-ray spectroscopy with HPGe detector), also these rock samples were analyzed with X-ray fluorescence to subdivided these rocks based on the major oxides proportions contained of each sample. The mean activity concentrations of naturally radionuclides were found in the igneous rock samples varied depending on the type of the igneous rock. For sedimentary rock samples, the activity concentrations were found high for quartz sandstone sample, which may be due to its high proportion of SiO2 and K2O. The estimated mean values of absorbed dose rate are within the permissible limit value. The findings indicate high dose level values in granite (rhyolite) and most of diorite (andesite) igneous rock samples while gabbro (basalt) igneous rock samples (except for one sample) record low levels of dose rate. All sedimentary rock samples have low dose rate (except for the quartz sand-stone sample).
Highlights
Many of the planets in the Solar System are mainly consist of rocks
The radionuclides activity concentrations of Ra-226, Th-232 and K-40 were determined in rock samples by Gamma-ray spectroscopy system includes hyper-purity germanium (HPGe) detector, and to estimate the doses originate from the existence of the natural radionuclides in the classified rocks
Occurring radionuclides were determined for eighteen igneous rock samples and twelve sedimentary rock samples using hyper-purity germanium (HPGe) detector
Summary
Many of the planets in the Solar System are mainly consist of rocks. Rocks are composed of minerals, both of them are the fundamental of the Earth’s crust structure. The content and the percentage of minerals contained in the rocks are studied by X-Ray Fluorescence (XRF). XRF reports chemical composition to indicate the content and the percentage of element dominate the rock samples and to classify them (Jamaluddin et al, 2018). The distribution of naturally occurring radionuclides depends on the type and origin of rocks and the processes which concentrated them (Bezuidenhout, 2019). Natural radionuclides are over a wide present in environment of the Earth, which is arranged geological formations in Earth’s crust (rocks, soil, water plants and air). The X-ray fluorescence analytical technique was used to analyze igneous and sedimentary rock samples from Al-Atawilah (north of Al-Baha region), and to classify them based on the chemical composition, which is one of the main characteristics of the rocks. The radionuclides activity concentrations of Ra-226, Th-232 and K-40 were determined in rock samples by Gamma-ray spectroscopy system includes hyper-purity germanium (HPGe) detector, and to estimate the doses originate from the existence of the natural radionuclides in the classified rocks
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