Air slab-correction for Γ-ray attenuation measurements

Gamma (gamma)-ray shielding behaviour (GSB) of a material can be ascertained from its linear attenuation coefficient (mu, cm(-1)). Narrow-beam transmission geometry is required for mu-measurement. In such measurements, a thin slab of the material has to insert between point-isotropic gamma-ray source and detector assembly. The accuracy in measurements requires that sample's optical thickness (OT) remain below 0.5 mean free path (mfp). Sometimes it is very difficult to produce thin slab of sample (absorber), on the other hand for thick absorber, i.e. OT >0.5 mfp, the influence of the air displaced by it cannot be ignored during mu-measurements. Thus, for a thick sample, correction factor has been suggested which compensates the air present in the transmission geometry. The correction factor has been named as an air slab-correction (ASC). Six samples of low-Z engineering materials (cement-black, clay, red-mud, lime-stone, cement-white and plaster-of-paris) have been selected for investigating the effect of ASC on mu-measurements at three gamma-ray energies (661.66, 1173.24, 1332.50 keV). The measurements have been made using point-isotropic gamma-ray sources (Cs-137 and Co-60), NaI(Tl) detector and multi-channel-analyser coupled with a personal computer. Theoretical values of mu have been computed using a GRIC2-toolkit (standardized computer programme). Elemental compositions of the samples were measured with Wavelength Dispersive X-ray Fluorescence (WDXRF) analyser. Inter-comparison of measured and computed mu-values, suggested that the application of ASC helps in precise mu-measurement for thick samples of low-Z materials. Thus, this hitherto widely ignored ASC factor is recommended to use in similar gamma-ray measurements. (C) 2017 Elsevier B.V. All rights reserved.