Nano-structured natural bentonite clay coated by polyvinyl alcohol polymer for gamma rays attenuation

AbstractThe 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 (۵۰, ۱۰۰ and ۱۵۰ 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 ۵۹.۷۹ 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 ۶۶۲ keV energy of ۱۳۷Cs; at ۱۱۷۳ and ۱۳۳۲ keV energies of ۶۰Co, gamma ray sources were determined by using NaI(Tl) scintillation detector. The experimental results showed that the ground bentonite pressed at ۱۵۰ 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.

Keywords:

Bentonite clay , Polyvinyl alcohol , Nanosize bentonite , Gamma rays attenuation