Effect of detector collimator and sample thickness on 0.662 MeV multiply Compton-scattered gamma rays

The simultaneous effect of detector collimator and sample thickness on 0.662 MeV multiply Compton-scattered gamma photons was studied experimentally. An intense collimated beam, obtained from 6-Ci 137Cs source, is allowed to impinge on cylindrical aluminium samples of varying diameter and the scattered photons are detected by a 51 mm×51 mm NaI(Tl) scintillation detector placed at 90° to the incident beam. The full energy peak corresponding to singly scattered events is reconstructed analytically. The thickness at which the multiply scattered events saturate is determined for different detector collimators. The parameters like signal-to-noise ratio and multiply scatter fraction (MSF) have also been deduced and support the work carried out by Shengli et al. [2000. EGS4 simulation of Compton scattering for nondestructive testing. KEK proceedings 200-20, Tsukuba, Japan, pp. 216–223] and Barnea et al. [1995. A study of multiple scattering background in Compton scatter imaging. NDT & E International 28, 155–162] based upon Monte Carlo calculations.