Investigation of gamma-ray shielding by double layered enclosures

Abstract

Risk of exposure to ionizing radiations is present during handling, transportation, storing and dumping of radioactive wastage. This risk necessitates the development of gamma-ray shielding enclosures with high attenuating efficiency and cost effective. Thus, to minimize such exposures from the radioactive wastage, it should be encapsulated in such enclosures before dumping. Lead (Pb) being high-Z material has been used in the construction of such enclosures. But, due to certain limitations of Pb, the new design of the radiation shielding enclosure has been introduced. In this design, the use of Pb has been reduced by using its combination with certain low-Z building materials. The basic idea behind the design is that the shielding enclosures should be constructed from the combination of both, low and high-Z materials in the form of double-layered-compound-slabs. This is due to dissimilar gamma-ray shielding behaviours (GSB) of low and high-Z materials. The enclosure made from two different materials in the form of layers, is termed as the double layered gamma-ray shielding enclosure (DLGSE). The GSB of DLGSEs made from the combination of Pb and selected samples of standard materials (Aluminium, Clay, Lime stone and NBS concrete) have been investigated in the thickness range (4.5–8.0 mfp) for γ-ray energy range (0.5–3.0 MeV). The objective of present work is to find the material for making of better DLGSE than Pb itself. Various energy and thickness dependent parameters such as: double-layered exposure buildup-factors, double-layered energy absorption buildup-factors, attenuation coefficients, effective atomic number, effective electron number per unit mass and the half value layer thickness have been analyzed during the investigation. Previously self-designed BUF-toolkit has been upgraded to DLBUF-toolkit. It is concluded that for broad beam geometry, the DLGSE in orientation, LZFHZ, 4LS-xPb for energies 0.5–1.0 MeV and 4Al-xPb for energies 2.0–3.0 MeV offers better GSB than Pb itself and its combination with other chosen materials. But, for narrow beam geometry the 4LS-xPb has been proved to provide the best GSB for the chosen range of thickness and energy. Thus, 4LS-xPb is recommended to replace the homogeneous gamma-ray shielding enclosure made from Pb.