Discrimination between low atomic number materials from their characteristic scattering of X-ray radiation

There are many applications within the agricultural, food and medical sciences where it is required to detect targets that absorb X-rays in a similar way to the background material and these are therefore not easy to detect in a transmission image. Scattered X-rays provide useful additional information as they have interacted with the material in question. Furthermore, the incident and scatter angles can be defined so as to characterize a small volume element without recourse to complex computer tomography techniques. The potential of scattering techniques has been partially rc:cognized within the medical sciences but remains largely unstudied in other application areas. This paper investigates the potential of distinguishing between different low atomic number targets from their scattering characteristics with a view to applying these techniques to food and agricultural applications. An experimental and simulation study are presented. The investigations use a polychromatic X-ray source to irradiate several low atomic number samples and a small area silicon photodiode to detect the scattered radiation. This geometry is reproduced within a simulation study based on a Monte-Carlo-based program. The results of the simulation and experimental study are shown, qualitatively, to be in close agreement with each other. These studies show that the intensity of scattered radiation, over a range of scattering angles, gives a greater contrast measure between low atomic number targets than a traditional transmission image. (C) 1997 Silsoe Research Institute.