Effect of low-Z absorber's thickness on gamma-ray shielding parameters

摘要

Gamma ray shielding behaviour of any material can be studied by various interaction parameters such as total mass attenuation coefficient (μ_m); half value layer (HVL); tenth value layer (TVL); effective atomic number (Z_(eff)), electron density (N_(el)), effective atomic weight (A_(eff)) and buildup factor. For gamma rays, the accurate measurements of μ_m (cm~2g~(-1)) theoretically require perfect narrow beam irradiation geometry. However, the practical geometries used for the experimental investigations deviate from perfect-narrowness thereby the multiple scattered photons cause systematic errors in the measured values of μ_m. Present investigation is an attempt to find the optimum value of absorber thickness (low-Z) for which these errors are insignificant and acceptable. Both experimental and theoretical calculations have been performed to investigate the effect of absorber's thickness on μ_m of six low-Z (10 ＜ Z_(eff) ＜ 14) construction materials (cement-black; cement-white; clay; red-mud; lime-stone and plaster of paris) at gamma-ray energies 661.66 keV, 1173.24 keV and 1332.50 keV. A computer program (GRIC2-toolkit) was designed for theoretical evaluation of shielding parameters of any material. Good agreement of theoretical and measured values of μ_m was observed for all absorbers with thickness ≤ 0.5 mean free paths, thus considered it as optimum thickness for low-Z materials in the selected energy range. White cement was found to possess maximum shielding effectiveness for the selected gamma rays.