Modeling and quantitative analysis of X-ray transmission and backscatter imaging aimed at security inspection

X-ray transmittance and backscatter imaging are important methods for detecting drugs and plastic explosives in the security-inspection field. In this study, we developed an analytical model based on Geant4 toolkit and verified it by measuring the energy spectrum and backscatter images. According to the model, we analyzed the imaging contrasts to detect concealed contrabands. The results show that the backscatter contrasts are significantly better than those of the transmission, especially in thinner organic materials. However, for shelters with strong absorption and scattering, the gaps become smaller. In addition, the variations in the contrasts with thickness appear to linearly increase in the transmittance imaging and nonlinearly grow until saturation in the backscatter imaging. Compared with traditional methods, our model, which is more accurate and complete, employs energetically distributed X-rays, instead of monochromatic X-rays, and involves multiple scattering effects. By using this method, we cannot only calculate and analyze the image characteristics of large amounts of contrabands in various system structures but also design and optimize instruments specially used to detect drugs and explosives.