Non destructive evaluation of selected polymers by multiple scattering of 662 keV gamma rays

In this paper, multiple scattering of 662 keV gamma photons from targets of Carbon, Aluminium, Iron, Copper and polymers (Polypropylene, Polycarbonate, Polymethyl methacrylate, Polytetraflouroethylene and Polyvinyl chloride) is studied experimentally. Backscattered photons are detected by a NaI(Tl) detector placed at an angle of 90° to the incident beam. The single scattered events are reconstructed analytically to extract multiple scattered photons from the measured spectra. We observe that the number of backscattered photons increases with an increase in target thickness, and saturates at a particular value of the target thickness. This saturation thickness decreases with increasing atomic number of the target. The saturation thickness of the multiple scattering is used to assign effective atomic number of polymers. The experimental results are compared with the results obtained by Monte Carlo N-particle simulation code.     

Experimental and simulated validation of the energy dependence of saturation thickness of multiple scattered gamma rays

Saturation thickness for multiple scattering gamma rays from multiple sources has been measured experimentally and simulated using the Monte Carlo N-Particle (MCNP) Code. Experimental measurements were performed using a collimated beam of gamma-rays from ⁵⁷Co, ²⁰³Hg, ¹³³Ba, ²²Na, ¹³⁷Cs, ⁶⁵Zn and ⁶⁰Co sources. The gamma rays were directed at rectangular aluminium targets of varying thickness. A NaI (Tl) scintillation detector placed at a backscattering angle of 180° was used to detect the scattered photons. The measured and calculated saturation thickness increases with increasing energy of incident gamma-rays. Experimental and simulated values are compared and are in good agreement.