TOTAL AND SECONDARY GAMMA DOSES IN ILMENITE-LIMONITE CONCRETE BIOLOGICAL SHIELDS

The attenuation and distribution of total gamma ray doses in a bulk shield of ilmenite-limonite concrete of density 2.9 g cm-3 have been measured. Direct, cadmium filtered and B4C filtered collimated reactor beam emitted from one of the horizontal channels of the ET-RR-1 reactor have been utilized in the present work. The distribution of the secondary gamma ray doses generated from the interaction of reactor neutrons of definite energy ranges has also been obtained for ilmenite-limonite concrete. The gamma doses were measured using 7LiF Teflon disc TL dosimeters. A semiempirical formula was derived to calculate total gamma dose distributions for bare, cadmium filtered and B4C filtered reactor beams at different thickness along the beam axis in ordinary concrete, with density 2.3 g cm-3, using the corresponding measured value in ilmenite-limonite concrete. Good agreement has been achieved between the values of the total gamma doses and those calculated using the derived empirical formula. Isodose curves were constructed for both the total gamma-ray doses and the secondary gamma-ray doses for ilmenite-limonite concrete shields together with the corresponding values for ordinary concrete shields. For comparison, ilmenite-limonite concrete is better than ordinary concrete for the attenuation of gamma-rays especially at deep penetration. The thickness of ilmenite-limonite concrete required to attenuate the total gamma dose intensity to a certain factor is approximately 94\% of the thickness when the shield is made of ordinary concrete. This ratio is somewhat different for secondary gamma doses as it is produced from neutrons with definite energy ranges.