Photon attenuation characteristics of radiation shielding materials

In the design and construction of installation housing high intensity radiation sources and other radiation generating equipment, a variety of shielding materials are used to minimise exposure to individual. Among the materials, lead is best known for radiation shielding characteristics due to their high density and atomic number. Commercial and barium enriched cement, apart from better compressive strength, smoother surface finish and high abrasion resistance, offers adequate shielding to gamma radiations. Although photon attenuation data are available in literature, it is necessary to test these commercially available material experimentally for their radiation shielding efficiency before putting them in to regular use. In the present work, attenuation characteristics of lead. commercial cement and barium enriched cement supplied by a manufacturing firm have been studied for photons of 662 and 1250keV from Cs-137 and Co-60. The radiographic sources of Cs-137 and Co-60 of radioactive strength of 260 and 30 mCi respectively were utilised in the present investigation. Experimental measurements were done with gamma radiography survey meter MR 4500A placed at a distance of 2 meters from the source. Attenuation coefficients for photons in commercial cement, barite and lead were determined experimentally through photon transmission measurements performed under broad beam counting geometry. The absorbers used were in form of thin sheets of lead, commercial cements and barite of uniform thicknesses. These thin sheets were weighed accurately on an analytical balance and from their measured area, thicknesses proportional to area density in gram.cm-2 were determined. The average thickness of each absorber varied from a few milligram to several gram per cm-2. Higher thicknesses were obtained by stacking the absorbers with each other. Each absorber of specified thickness was interposed between the source and detector such that the primary beam is incident normally on its surface. The thickness of the absorber was increased in steps by adding absorbers as indicated earlier. From the transmitted (I) and the incident photon intensity (I0), for a thickness 'x' of the absorber, the photon attenuation coefficient μm is calculated by the following expression: μ=ln(l0/l)X. The values of photon attenuation coefficients thus are obtained. The overall uncertainty of the measured values was estimated to be around 5% and had the following components: the counting statistics for I and I0 measurements and thickness uniformity of the absorbers. However, as the data for commercial cement and barite are not available, no comparison have been made with the theoretical values. Thus the derived values of attenuation coefficients of the tested materials can be utilised in compilation of shielding thicknesses for any radiation facilities where these materials are to be used. (author)