Apply X-Ray Fluorescence and γ-Ray Spectroscopy to Analyze Igneous and Sedimentary Environmental Samples of Al-Atawilah (Al-Baha), Saudi Arabia

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 pre-pared 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 SiO 2 and K 2 O. 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 sandstone sample).


Introduction
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 rocks have great economic uses, also, many rocks are frequently used decoratively especially crystalline igneous rocks and marble. The defining features of any rock, and thus the means by which it can be recognized and named, are a direct result of how it is formed. Igneous rocks are created when magma or lava crystallizes. Whereas Sedimentary rocks are formed by weathering and erosion of pre-formed rocks, transportation of the grains by the wind or a river system, and finally accumulation in water or on the land (Pellant & Pellant, 2014). 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). When the rocks are disintegrated by natural process, the resulting radionuclides are carried to the soil by rain and flows (Olufunmbi et al., 2016;Khan et al., 2018). Ra-226 and its daughter product effects are 98.5% of the radiological of U-238 series, the contribution of Ra-226 is often referred to instead of U-238 (Khandaker et al., 2017).
In the present study, 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. Silica (SiO 2 ) is the vast majority mineral and its proportion is the most useful criteria of rock's classification. 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.

X-Ray Fluorescence Spectroscopy
X-ray fluorescence (XRF) spectroscopy is a non-destructive instrumental technique that enables to determine the chemical composition of a sample based on  Figure 1 shows X-ray fluorescence mechanism of an atom. An X-ray primary beam irradiates the sample and excites each chemical element to produce fluorescent (or secondary) X-rays. These emitted X-rays are characteristic of the atom, that give the qualitative analysis of the element.
The energy of the emitted X-ray photon is the energy difference between the two levels (initial and final) involved in the electronic transition. The X-ray intensities of an unknown sample are compared to an appropriate standards, this provides quantitative analysis of the element. The measured sample can be of any form, powder, solid, liquid, and manufactured materials (such as wire and rod), etc. (Bertin, 1975;Kalnicky & Singhvi, 2001).

Gamma-Ray Spectroscopy
The samples have been preparing for the gamma spectrometric measurements as 2) All rocks samples were obtained at depth of 5 cm from the study region.
The collected samples were dried, pulverized and then sieved through less than 1mm-mesh size (IAEA, 1989).
3) All crushed sieved rock samples were filled into Marinelli beakers, weighed and hermetically sealed for more than one month, in order to achieve the secular equilibrium between Ra-226 and Th-232 and their progenies (Onjefu et al., 2017;Chowdhury et al., 2020).
The gamma-ray spectroscopy is a rapid and nondestructive analysis used to measure of radionuclides activity concentrations in the rock samples. The detector had resolution of 2 keV at 1332.5 keV of Co-60 and relative efficiency of 25%. The detector is placed in a cylinder heavy lead to lessen the values of radiation background. The lead shield contains an internal concentric of copper to Figure 1. X-ray fluorescence mechanism of an atom (Kalnicky & Singhvi, 2001). avoid interference X-rays by lead (Saher et al., 2013;Rosianna et al., 2020). For successful operation of HPGe detector, it is cooled to cryogenic temperature at least 12 hours before making measurements by liquid nitrogen (LN2) of −196˚C = 77˚K.
The activity concentration (A C ) was carried out using the following formula where N C is the net count area of the gamma line for the measured sample (counts/second), m is mass of the sample,  is the absolute efficiency of the spectrometer at the photo-peak energy and β is the probability of emission of the gamma ray. The activity concentration of each nuclide is estimated from the where C Ra , C Th and C K are respectively the activity concentrations of 226 Ra, 232 Th and 40 K.

Classification of the Igneous and Sedimentary Rocks Samples Based on Their Chemical Composition
Rocks are important in mapping of natural resources. Igneous rocks are encountered in geothermal environments. Igneous rocks especially very recent are  (Mibei, 2014).
The igneous and sedimentary rock samples under investigation were classified based on the chemical composition obtained from X-ray fluorescence technique.
Silica (SiO 2 ) is the vast majority mineral and its proportion is the most useful criteria of rock's classification.  2) Greywacke: has about 66.06% of silica, sample SED20.
Sedimentary rocks form up to 66% of the earth's crust. They consider the most of the rocks on the earth's surface and are mainly found on the ocean floor basins which accounts to 70% of total area of the earth. Igneous rocks form the majority of 34% (Ehlers and Blatt, 1997). Also, the igneous and sedimentary rocks are classified based on chemistry and minerals, environment of formation and how they are formed.

Activity Concentrations
The activity concentrations of the rock samples under studying were tabulated in

Absorbed Dose Rate
Absorbed dose rate values for rock samples were shown in Table 4, and the following observations can be indicated:

Conclusion
The results of chemical analysis employing X-ray fluorescence spectroscopy The findings indicate the high dose rate in the granite (rhyolite) samples and most diorite (andesite) samples, therefore it is recommended to limit their usage in building materials and other uses, while the dose rate levels were low in all Journal of Geoscience and Environment Protection gabbro (basalt) samples (except for one sample), thus they are safe to use as well as all sedimentary rocks samples reported low values of the dose rate values (except for the quartz sandstone sample). The results of this study will help to explain the distribution of natural radionuclides in different rocks types of Al-Baha region.