DETERMINATION OF GAMMA-RAY RELAXATION LENGTHS FOR DISK COLLIMATED BEAM AND INFINITE-PLANE MONODIRECTIONAL SOURCES IN DIFFERENT CONCRETE SHIELDS

This work is concerned with a comparative study of the distribution and attenuation of total and secondary doses of gamma-rays in ordinary, ilmenite and ilmenite-limonite concrete shields. The data were obtained using a direct, cadmium filtered and boron carbide filtered beam of reactor neutrons. All measurements were performed using a (LiF)-Li-7 Teflon TLD dosimeter. The results showed that ilmenite concrete is a much better attenuator for gamma-rays. The effect of the build-up factor is more pronounced in ordinary and ilmenite-limonite concretes than in ilmenite concrete. A group of curves were constructed which give directly the shape and thickness of each concrete required to attenuate the intensity of total gamma-doses for a bare reactor beam to specific values. The thickness of ilmenite concrete necessary to decrease the total gamma-dose at a certain value is 58 and 67\%, respectively, of the thickness required when the shield is made from ordinary and ilmenite limonite concrete, respectively. In addition, the relaxation lengths of gamma-rays in ordinary, ilmenite and ilmenite-limonite concretes were calculated using infinite plane monodirectional sources and disc collimated beam.