Assessment of behavior for aluminum-boron carbide composite materials agaisnt radiation, investigation by XCOM software program, suggestion of a new hybrid composite radiation shielding material

This doctorate thesis aimed to assess how aluminum-boron-carbide composite material to be used for shielding different types of ionizing radiation behaves and to suggest a new material for this purpose. Ionizing radiation sources are widely used in various industrial, medical, agricultural and research fields. Depending on its purpose of use, radiation may be of various types and at various energy levels. One of the most important methods to protect people working involve radiation and the public from radiation is to shield the source of radiation or the workplace where it is used. Since radiation's interaction with a material depends on its type and energy level, there are various materials used for shielding. Such fields as nuclear reactor and aerospace may cause exposure to various types of radiation at the same time. Providing efficient shielding by means of a single material in such multiple radiation areas is useful for decreasing the volume of the shielding material and lowering the costs of shielding. Although lead is the widest used radiation shield material, it causes toxic effects harmful to human health. Furthermore, RoHS Directive passed by the E.U. restricts the use of lead in various fields, and it is planned to impose an all-out ban of lead in the future. In this context, this doctorate thesis suggests a material which can be an alternative to lead and be efficient in shielding various types of radiation. Experimental works were performed on aluminum-boron carbide (Al-B4C) material for the original purpose of this doctorate thesis. The material in question contained B4C compound in four different volume ratios (5%, 10%, 15%, 20%) and in five different particle sizes (average 3 µm, average 53µm, 75 to 150 µm, 150 to 250 µm, average 500 µm). Shielding behaviors of all these types of the material against gamma, neutron and beta radiations were examined. In other words, the effect of the particle sizes of B4C compounds on shielding behavior and experiments conducted with gamma, neutron and beta radiations are original contents of this doctorate thesis. Results obtained from aluminum-boron-carbide (Al-B4C) material were used for working on aluminum-boron carbide-tungsten carbide material and examining its shielding behavior under gamma, neutron and beta radiations. This choice of material is an original content of this doctorate thesis. Three different radioisotope sources emitting gamma radiation at different energy levels were used. Experiments with gamma radiation were performed by Am-241 at low energy level (60 keV), by Co-60 at high energy level (two peaks at 1.17 and 1.33 MeV, average 1.25 MeV), and by Cs-137 at medium energy level (662 keV). Experiments with neutron radiation were conducted by using the Pu-Be neutron source within Howitzer. Average energy of the neutrons emitted by this source was approximately 4 MeV. The radioisotope source used for the experiments with beta radiation was Sr/Y-90. Maximum beta energy emitted by the said radioactive source was 2.28 MeV. Transmission technique was employed for these experimental works on gamma and beta radiations to find linear attenuation and mass attenuation coefficients and on neutron radiations to find macroscopic effect cross-section values, for each type of material. The values in question were used for calculating half-value thickness (HVT) of each type of material depending on the type of radiation applied. Furthermore, theoretical calculations were made by using the internationally recognized XCOM software to calculate theoretical gamma mass attenuation coefficients. These theoretical gamma mass attenuation coefficients calculated for the composite materials were compared with the theoretical values calculated by XCOM software. Results of the experiments conducted on gamma sources indicate that as the size of particles of B4C compound within Al-B4C compound increases, radiation absorbance of the composite material decreases. As energy level of gamma radiation increases, the effect of particle size decreases. However, as volume ratio content of B4C within the composite material increases, gamma radiation absorbance of the composite material decreases. The decrease in question is higher for gamma radiation at low energy level, and lower for gamma radiation at high energy level. Experiments conducted on Al-B4C-WC hybrid composite material indicate that as the amount of WC in the material increases, its absorbance of gamma radiation increases. Furthermore, the theoretical mass attenuation coefficients calculated by XCOM software program for gamma radiation are similar to the experimental theoretical mass attenuation coefficients found. Most of the differences between these two sets of coefficients are below 3%, all of them are below 6%. Experiments conducted on neutron radiation for Al-B4C composite compound indicate that as volume ratio and particle size of B4C compound of the said composite material increases, its absorbance of neutrons increases. As B4C and WC ratios as volume ratios in Al-B4C-WC hybrid composite material increase, its absorbance of neutrons increases. Experiments conducted on beta radiation indicate that as volume ratio of B4C compound within Al-B4C composite material increases, its absorbance of beta radiation increases. Furthermore, as volume ratios of B4C and WC compounds within Al-B4C-WC hybrid composite material increase, its absorbance of beta radiation increases. The mass attenuation coefficients found for the composite materials by experiments were compared with the mass attenuation coefficients found for pure aluminum. If WC compound is added at certain ratios in Al-B4C composite materials, the shielding effect of the said materials against different types of radiation increases, and their density increases too. Density of material is an important subject in space, aeronautical and nano technologies. Therefore the amount of WC added in such compound must be limited. This doctorate thesis arrives at the original finding that the results of the experiments performed for this study indicate that hybrid composite materials produced by adding WC by 5% to 10% in Al-B4C composite material can be used as an efficient shielding material against fields of mixed radiations.