Monte Carlo Simulation for Dual-energy X-ray Inspection System and Electron-beam Energy Determination

Abstract

This thesis presents a Monte-carlo simulation related to the accelerator: (i) developing a detecting algorithm in the cargo inspection system using dual-energy X-rays

(ii) designing a device for determining electron-beam energy using the charge-deposition distribution.First, we propose a method to identify materials in a dual energy X-ray (DeX) inspection system. This method identifies materials by combining information on the relative proportions T of high-energy and low energy X-rays transmitted through the material, and the ratio R of the attenuation coefficient of the material when high-energy x-rays are used to the material when low energy x-rays are used. In the Monte Carlo N-Particle Transport Code (MCNPX) simulations using the same geometry as in the real container inspection system, this T vs. R method successfully identified tissue-equivalent plastic and several metals. In further simulations, the single-shot mode of operating the accelerator distinguished materials better than did the dual-shot system.Second, a method for determining electron-beam energy is presented. Electron energy is one of the principal parameters influencing the charge-deposition distribution (CDD) within a material penetrated by electron beams. The CDDs of electrons with energies from 5 to 60 MeV passing through aluminum absorbers were calculated using the MCNPX code, and experiments were performed at the Pohang Accelerator Laboratory (PAL) for electron beams of 50, 55, and 60 MeV passing through aluminum absorbers consisting of 4 plates separated by air gaps. To develop a useful device for measuring the electron beam energy, the most probable charge-deposition depth, xm, and the maximum charge deposition, ym, were determined from both the MCNPX and the experimental CDDs.