Investigation of Gamma-Ray’s Transmission Geometries for the Measurement of Attenuation Coefficients

Abstract

Abstract For the measurement of attenuation parameters of any material for gamma (γ)-rays, the narrow-beam transmission geometry is one of the essential requirements. Linear attenuation coefficient (μ, cm−1), half value layer thickness and mean free path are some fundamental parameters used for the analysis of γ-ray attenuation behaviour of any material. The complete experimental setup used to measure these parameters is termed as γ-ray transmission geometry. The geometrical parameters such as the size of collimator aperture, thickness of sample (absorber), source to absorber (SA) distance, absorber to detector distance and source to detector distance (STD) are deciding factors for the nature of γ-ray transmission geometry. A novel geometrical parameter, scattered-to-transmission ratio (STR), has been proposed in this investigation. STR provides qualitative information of various geometrical parameters. It provides influence on the nature of transmission geometry for experimental measurements by various geometrical parameters and buildup factor. To investigate its influence, STR values have been analysed by varying sizes of collimator aperture between 3 and 12 mm and absorber thicknesses between 20 and 280 mm for fixed SA and STD. Six standard building materials (cement black, cement white, clay, red mud, lime stone and plaster of paris) have been used for the investigation. The point isotropic γ-ray sources Cs-137 (3700 M Bq) and Co-60 (370 M Bq) have been used in this study. It has been found that STR provides better information of scattered γ-rays by the material than its buildup factor (B). Additionally, CSTR (the critical value of STR) serves as an extensive parameter to distinguish between narrow-beam (good) and broad-beam (poor) γ-ray transmission geometries.