This study aims to evaluate the specific activity levels in soil and shore-sediment samples due to natural radionuclides; ²³⁸U, ²³²Th and ⁴⁰K, and man-made ¹³⁷Cs of Al–Nigella site, Marsa Matrouh government, Egypt. Soil and shore sediment sample selection, preparation, energy and efficiency calibration, Minimum Detectable Activity (MDA) of the HPGe detector was carried out according to the standard approaches. The activity concentrations of the samples ranged from 3.16 ± 0.04 to 36.28 ± 0.83 Bq kg⁻¹ for ²³⁸U series, 0.582 ± 0.01 to 33.35 ± 0.62 Bq kg⁻¹ for ²³²Th series and 7.38 ± 0.18 to 477.64 ± 8.12 Bq kg⁻¹ for ⁴⁰K and 0.088 ± 0.002 to 3.98 ± 0.09 Bq kg⁻¹ for the artificial ¹³⁷Cs. The Radiological contour maps for Al–Nigella were drawn using Surfer_13 software and the hazards index was estimated according to the results of the radioactivity measurements and their levels. All results obtained are within the permissible world average values and compared with the activity concentrations in different countries. The values of the calculated air absorbed gamma dose rate D, Annual effective dose E, Radium equivalent (Ra_eq), External hazard index (H_ex) and Gamma index (Iγ) are below the average international recommended limits as reported by UNSCEAR 2008.

Wadi El Reddah has radiation exposure due to the presence of different types of complexed rocks along with a huge sector of Hammamat sedimentary rocks, monzongranites of Gabal El Reddah, perthitic leucogranites of Gabal Gattar, as well as swarms of post-granitic dykes. The studied sediments show wide variation in their uranium, thorium, radium (eU), and potassium (K, %) contents. The U content ranges from 5 to 51 ppm with an average of 17.33 ppm; the Th content, from 16 to 141 pp with an average of 32.47 ppm. Ra (eU) varies from 5 to 26 ppm with an average of 9.56 ppm, and the potassium content ranges from 2.19 to 4.41% with an average of 3.19%. The absorbed dose rate (D), annual effective dose equivalent (AEDE), radium equivalent activity (Ra_eq), external (H_ex) and internal (H_in) hazard indices, and the activity gamma index (I_γ) caused by gamma-emitting natural radionuclides were determined from the obtained values of the ²³⁸U, ²³²Th, and ⁴⁰K content. Most of the studied samples were out of range with respect to the universal standards.

Abu Garadi area is mainly represented by metasediments, alkali feldspar granites and stream sediments. The granitic mass described different degrees of hydrothermal alterations like albitization, greisenisation, hematitisation, silicification and koalinitisation which are mostly restricted to the faults. Uranium mineralisation in these granitic rocks is mainly controlled by the sheared granite parts. Various radionuclides from uranium decay series such as (²³⁸U, ²³⁴U, ²³⁵U, ²³⁰Th, ²²⁶Ra) and ⁴⁰K in the altered granite of Abu Garadi area that located in central Eastern Desert, Egypt are used to localise uranium accumulation sites in this pluton. Uranium and Thorium contents indicate that these altered granites have high thorium and high uranium granites. Th/U ratios vary between 0.81 and 5.79 with an average of 2.64, which suggests the presence of these samples in the transitional oxidation-reduction zone as evidenced by Th/U ratios>2 and reduction zone as suggested by Th/U ratios<2, respectively. ²³⁸U/²³⁵U, ²³⁴U/²³⁵U, ²³⁴U/²³⁸U, ²³⁰Th/²³⁸U, and ²²⁶Ra/²³⁰Th activity ratios confirm that most samples of Abu Garadi altered granite lie in the U-accumulations zone. All investigated samples clarify that uranium-series disequilibrium is a technique to trace the recent migration of uranium in these altered granites by the characterisation of the oxidation-reduction boundary.

The shielding characteristics of natural bentonite can be enhanced based on calcination and ball-milling processes for protection against gamma radiation. The calcination process increases the content of the oxide, which enhances the mass attenuation coefficient; however, the elimination of water and organic matter from bentonite clay structures increases the particle size, where large particle size has a negative effect on this mass attenuation coefficient. Therefore, the calcinated bentonite has been ball-milled to reduce the particle size and improve the attenuation properties of natural bentonite. Furthermore, the calcination process occurs at 700°C for 2 h because dehydration is completed above 500°C while dehydroxylation is observed at 700°C. Therefore, the shielding parameters have been determined for calcinated, ball-milled, pressed bentonite clay samples according to different gamma-ray energies (662, 1173, and 1332 keV), where the experimental setup is based on narrow beam transmission techniques with two sources (¹³⁷Cs and ⁶⁰Co). In addition, the particle size of bentonite clay has been characterized using X-ray diffraction patterns depending on two different methods: dynamic light scattering and Williamson-Hall size analyses. This study shows that the calcinated, ball-milled bentonite pressed at 150 bar has the highest linear and mass attenuation coefficients of μ = 0.13 cm⁻¹ and μ_m = 0.082 cm²/gm, respectively. Moreover, the experimental and theoretical investigation of the mass attenuation coefficient is in good agreement.

Gabal Abu Garadi area is covered by metasediments, alkali feldspar granites and stream sediments. Geochemically, silicification, desilicification, sericitisation, fluoritisation and Na-metasomatism are the main alteration features of alkali feldspar granites. The activity concentration of ²³⁸U in alkali feldspar granites ranged between 1.7 ± 0.1 Bq g⁻¹ and 3.9 ± 0.3 Bq g⁻¹; between 1.7 ± 0.2 Bq g⁻¹ and 9.4 ± 1.4 Bq g⁻¹ for ²³⁴U and between 0.012 ± 0.0002 Bq g⁻¹ and 0.09 ± 0.0001 Bq g⁻¹ for ²³⁵U. The activity concentration of ²²⁸Th ranges between 1.3 ± 0.1 Bq g⁻¹ and 3.6 ± 0.8 Bq g⁻¹; between 1.5 ± 0.2 Bq g⁻¹ and 2.7 ± 0.7 Bq g⁻¹ for ²³⁰Th and between 1.8 ± 0.3 Bq g⁻¹ and 4.1 ± 0.4 Bq g⁻¹ for ²³²Th. The variability in Chemical Index of Alteration (CIA) with U, Th, ²³⁰Th/²³⁸U and ²³⁰Th/²³⁴U for the studied altered granite indicates that U and Th concentrations increased with increasing alteration especially in the silicified and desilicified samples. Changes in U, Th, ²³⁰Th/²³⁸U and ²³⁰Th/²³⁴U suggest the role of alteration processes in uranium and thorium mobilisation though thorium is geochemically less mobile or immobile. Thorium mobilisation could be controlled by adsorption in the alteration products of Abu Garadi granites such as clay minerals, manganese and iron oxides. In contrast, ²³⁰Th/²³⁸U and²³⁰Th/²³⁴U decreased with increasing CIA values suggesting uranium accumulation. ²³⁴U/²³⁸U ratios were in equilibrium in most samples; this might suggest the effect of severe chemical weathering or alteration processes that leads to the leachability of the two radionuclides (²³⁴U, ²³⁸U) with the same ratio probably during kaolinisation processes. In contrast, ²³⁰Th/²³⁸U and²³⁰Th/²³⁴U>1 were in disequilibrium, suggesting the changes in the physicochemical conditions accompanying the different alteration processes.