Radiation attenuation by porous materials

In this thesis, silica carbur, aluminum, magnesium open cell metallic foams, a soil sample, standard Ottowa sand and a porous medium include spherical glasses in 0,5mm diameter as porous media were examined by using geometric gamma transmission technique with narrow beam. Gamma transmission technique based on a gamma-radiation emitting from the source of the photons can pass through the material with the penetrated material to be inspected which is obtained by comparing the radiation data. This method should be fast as well as the prefferred one is a non-destructive method with high accuracy. Gamma transmission technique are widely used in scientific research, industry, medicine and in agriculture. In industrial lead, aluminum, steel, such as determination of material thickness, in some imaging devices for medical gamma transmission method is used in measurements with the gamma camera underlying. In agriculture, The useful information about soil porosity and soil retention are achieved by using this method. Developing new multifunctional materials in recent years for nuclear systems has become increasingly critical owing to the high demand on better shielding in extreme environments. Radiation shielding materials and components of shielding structures should possess good mechanical properties, long-term reliability, good fabrication and joining properties with suitable thermophysical characteristics. Particular emphasis must be given to low density, high radiation tolerance and energy absorption capabilities due to new mission criteria in nuclear industries. Porous media are encountered literally in every day life, in technology, and in nature. Sand, sandstone, soil, ceramic, foam rubber, bread and lungs, are examples of porous materials encountered in practice. The extraction and filtering of underground oil , geothermal energy, insulation materials, air and spacecraft in flight and the prevention of heat during launch are the application fields of porous media. Also porous materials are used in fields such as the attenuation of the radiation shielding of nuclear waste and storage . The porous media as lightweight material can be used shielding of radiation. Studies on this subject are made by using the gamma attenuation mechanism with narrow beam geometry. The basis of this master's thesis is the investigation of structures of various porous media by using gamma transmission technique. The experimental works were performed on the existing narrow beam geometry in ITU Energy Institute 60Co gamma-ray source and gamma permeability apparatus are used. In this study, three kinds of metalic open cell foams, soil, standard sand and a porous medium that includes spherical glasses were used as porous media and the water was used for sturation of media. In order to ensure a homogeneous porosity of soil sample, soil was passed through a pre- screening process, other materials used in the experiments were placed directly plexyglass container in experimental setup. Firstly, the gamma transmission measurements were carried out with dry porous materials, then all of the materials were saturated by water and the gama transmissions from saturated materials were measured in the same experimental conditions. In all of the experiments, the measurements were done in the three vertical points of the center line of the materials. The measurements were achieved by using NaI(Tl) scintillation detector, the collimators providing the narrow beam condition and a multichannel analyser. Firstly, by inserting a 60Co radioisotope into source collimator in the system without material three successive counts were taken, so the source intensity (I0) was found. Then, respectively, three times three consecutive counts from the three different levels of silicon carbide, alumina and magnesium metalic open cell foams were counted by inserting materials between the collimators. By using this counts, the relative counts intensities were calculated and by taking into consideration material thickness the linear attenuation coefficients were found for every metalic foams. In the another part of the experiments, it is aimed to examine the porosity of these materials. To find this, saturating the materials and evaluating informations from this and experimental results with dry materials is a necessary. To make saturation operation, firstly dry materials were inserted into a plexyglass container. Then water was poured into the container slowly until water level is higher materials up level by one centimeter. With this saturated new material counts were taken by using 60Co radiation source in the narrow beam geometrical gamma transmission system. In this experiment, the prismatic SiC and alumina blocks were used. By using linear attenuation coefficients for dry and saturated materials experiment results and by inserting these informations into basic equations, the porosities were calculated for each three points of two kinds of materials. Beside the calculation of the porosities of foams, the attenuation of the different thicknesses of silicon carbide and alumina were examined against 60Co radiation source, also the narrow beam geometry gamma transmission was used with this experiment. The relative counts were calculated and shown by exponential relative counts versus thickness. The gamma transmission measurements for Samsun Province's soil sample, standard Ottawa sand and glass beads were repeated with the same experimental conditions. The attenuation of radiation and the porosities of all porous materials were found. The soil sample, the standard Ottawa sand, glass beads contain SiO2 and also SiC metalic foam has silisium. So, it was possible the comparison of these porous materials in terms of the radiation attenuation and the structure of porousity. The results revealed that all the work has been interpreted as given in comparative tables and graphs.