An experimental study of energy dependence of saturation thickness of multiply scattered gamma rays in zinc

Abstract

The present measurements have been carried out to study the energy dependence of saturation thickness of multiply scattered gamma photons from zinc targets of various thicknesses. An inverse response matrix approach has been implemented to convert the observed pulse-height distribution of a NaI (Tl) scintillation detector to a photon spectrum and hence to improve the statistical error. These results in extractions of intensity distribution of multiply scattered events originating from interactions of 662 keV photon with thick target of zinc material. The observed pulse-height distributions are a composite of singly and multiply scattered events. To evaluate the contribution of multiply scattered events only, the spectrum of singly scattered events contributing to inelastic Compton peak has been reconstructed analytically. The scattered photons have been detected by a properly shielded NaI (Tl) gamma ray detector placed at different angle to the incident beam. The saturation thickness at which the number of multiply scattered events saturates has been measured. The signal-to-noise ratio and multiple scatter fractions have been found to be decreasing with increasing target thickness. The self-absorption correction factor improves the multiply scattered photon intensity but not the saturation thickness. The same experiment has been repeated with HPGe detector at 90° scattering angle. The results obtained with NaI (Tl) and HPGe detector show the same trend. The experimental results have been found to support the Monte Carlo calculations.