Measurement of exposure buildup factors: The influence of scattered photons on gamma-ray attenuation coefficients

摘要

Scattered photon's influence on measured values of attenuation coefficients (μ_m, cm~2g~(-1)) for six low-Z (effective atomic number) building materials, at three photon energies has been estimated. Narrow-beam transmission geometry has been used for the measurements. Samples of commonly used engineering materials (Cements, Clay, Lime-Stone, Plaster of Paris) have been selected for the present study. Standard radioactive sources Cs~(137) and Co~(60) have been used for obtaining y-ray energies 661.66, 1173.24 and 1332.50 keV. The optical thickness (OT) of 0.5 mfp (mean free path) has been found the optimum optical thickness (OOT) for μ_m-measurement in the selected energy range (661.66-1332.50 keV). The aim of this investigation is to provide neglected information regarding subsistence of scattered photons in narrow beam geometry measurements for low-Z materials. The measurements have been performed for a wide range of sample-thickness (2-26 cm) such that their OT varies between 0.2-3.5 mfp in selected energy range. A computer program (GRIC2-toolkit) has been used for various theoretical computations required in this investigation. It has been concluded that in selected energy-range, good accuracy in μ_m-measurement of low-Z materials can be achieved by keeping their sample's OT below 0.5 mfp. The exposure buildup factors have been measured with the help of mathematical-model developed in this investigation.