The main goal of this work is to find natural rock materials that can be used as effective gamma rays shielding at minimal cost, reliability and wide applications. It must be at particular weight and volume (lighter and more protection). Natural bentonite clay can be used as shelters from nuclear waste because of its large availability and low cost. Bentonite clay was used in two forms naturally as it is from its ores and in ground phase. Natural bentonite was cut into cylindrical pellets at different thicknesses; also, the other form pressed into cylindrical pellets with different thicknesses and different pressing pressures (50, 100 and 150 bar). The different samples are coated with polyvinyl alcohol polymer to prevent nuclear waste leakage through porosity of clay. Chemical analysis and density are measured for all samples. Bentonite clay was found naturally in nanometer scale because it is formed from volcanic ash deposits. The nanoparticle size was determined by dynamic light scattering and Williamson-Hall size analysis using XRD patterns and the help of X-powder program. The particle size of natural bentonite was found to be 59.79 nm. The microstructure was characterized by scanning electron microscope and transmission electron microscopy. The linear and mass attenuation coefficients of nano-structured bentonite clay (natural and pressed) were determined at 662 keV energy of 137 Cs; at 1173 and 1332 keV energies of 60 Co, gamma ray sources were determined by using NaI(Tl) scintillation detector. The experimental results showed that the ground bentonite pressed at 150 bar gave the highest linear and mass attenuation coefficients than other samples. The theoretical and the experimental calculations of mass attenuation coefficient were found to be in a good agreement.

The studied area at Wadi Nugrus, Southeastern Desert, Egypt, is located between lat. 24˚41'00'' and 24˚41'35''N and long. 34˚36'47'' and 34˚37'09''E. The rock types are represented by layered metagabbros, biotite schists, gneisses, granodiorites, and Muscovite granites. The muscovite granite of Wadi Nugrus, is small exposure in size (~5.0 km 2), emplaced along NW-SE trend, with about 0.5-4.5 Km in length and 100-250 m in width and intruding the biotite schists. The studied muscovite granite is composed mainly of plagioclases, potash feldspars, quartz, biotite and muscovite. The recorded minerals assemblage can be classified into secondary U-minerals (uranophane and meta-autunite), U-bearing minerals (uranothorite and columbite) and accessory minerals (zircon, flourite, allanite, zinnwaldite and hematite). The U/eU is more unity where, the measured chemical uranium is higher than the measured equivalent uranium in the most analyzed samples especially in trenches, which reflect disequilibrium state. The activity concentrations range from 251.72 to 1096.2 Bq•kg −1 for 232 Th, from 494 to 2593.5 Bq•kg −1 for 226 Ra, and from 1314.6 to 1846.7 Bq•kg −1 for 40 K. The obtained radiological data show that the average internal and external hazard indices are 9.11 and 5.78, respectively which are more than unity and highly exceeding the permissible limits (International Commission on Radiation Protection, ICRP). The internal and external hazards are mainly due to 226 Ra nuclei while the absorbed dose rate (nGy/h) is related to 232 Th nuclei. The contributions of the three nuclei in the total absorbed dose rates and internal and external hazardous, for 226 Ra, it contributes by 72% in H in , 57% in H ex and 55% of D R , for 232 Th it contributes by 24% in H in , 37% in H ex and 36.9% of D R , while for 40 K it contributes by 4.1% in H in , 6.4% in H ex and 8.1% of D R .

This Radiation shielding capability in terms of mass and linear attenuation coefficients, half value layer, tenth value layer, and mean free path haven been evaluated for natural bentonite coated with polyvinyl alcohol polymer (PVA) using Monte Carlo simulation (MCNPX) and XCOM program. All data were determined at gamma photons energies 662, 1173 and 1332 keV emitted from point sources of 137 Cs and 60 Co, respectively, and compared with calculated experimental data. XCOM results of mass attenuation coefficients showed better agreement with experimental data in comparison with MCNPX code. The relative deviations between experimental and theoretical mass attenuation coefficients are 4.3, 2.5 and 1.25 % at 662, 1173 and 1332 (keV) while deviation between simulated and experimental mass attenuation coefficients are -3.1, -10.96 and -10.35 % at the same energies, respectively. The relative deviation between simulated shielding factors HVL, TVL and MFPwith experimental data exhibit the same behavior as mass attenuation coefficient and having average relative deviations percentage equal to 2.5, 13.4 and 13.8 % at the studied energies, respectively.

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Calcination process is a method used for gamma rays mass attenuation coefficient enhancement of natural bentonite clay nano-particles. This process eliminates water and organic matter from bentonite clay structure which have low mass attenuation coefficient values. There are two opposite effects on mass attenuation coefficient values; oxides content increases after calcination process which enhances mass attenuation coefficient values and particle size of calcinated bentonite increases which decreases mass attenuation coefficient values. In order to enhance mass attenuation coefficient value for natural bentonite, a physical ball milling must introduced after calcination process that decreases particle size. Calcination process is done at 700 ̊C for two hours because dehydration is completed above 500 ˚C while dehydroxylation observed at 700 ˚C. Mass attenuation coefficients are measured for calcinated and ball milled bentonite clay at different energies (662, 1173 and 1332 keV) and different pressing pressures (50, 100 and 150 bar). Narrow beam transmission technique and two different sources (Cs-137 and Co-60) are used for mass attenuation coefficient measurements, also particle size are measured by two different methods dynamic light scattering and Williamson-Hall size analyses using XRD patterns. All samples are coated by polyvinyl alcohol polymer.