Studying the effect of the scanned objects’ location on material discrimination in a dual-energy cargo inspection system

Abstract

Dual-energy X-ray radiography is an important inspection technology in imaging large cargos for finding illegal materials. A useful aspect of dual-energy X-ray radiography is the possibility of discriminating and identifying materials with different atomic numbers which can be obtained by imaging large cargos at two different X-ray energies (normally above 3 MeV). The performance of both single and dual-energy radiography depends on many factors such as beam energy and filtration, radiation dose, scanned object size, the content of the object, etc. One of the parameters that can affect the quality of the material discrimination is the location of the scanned objects (different heights from the ground). It is due to the fact that the generated X-ray beams from the Linac are angle dependent and therefore, energy spectrums vary at different angles. In this work, our main goal was to find equations for material discrimination curves as a function of height for graphite, aluminum, steel, and lead materials. After obtaining simulated and experimental curves for a range of heights, we searched for best-fitting polynomial equations and finally the best equation for each material was obtained. Our results showed that there is a good agreement between the simulated and experimental curves compared to those obtained from the fitted equations. According to obtained results, material discrimination curves can be obtained for a range of heights using the fitted equations without performing any further simulation and experimental processes. This can be very helpful in reducing calibration time and increasing calibration accuracy in inspection systems.