DEVELOPMENT ON FAST NEUTRON RADIOGRAPHY SYSTEM BY USING PORTABLE NEUTRON GENERATOR

Most of the concealed explosives and hazardous materials share the similar physical characteristics with the benign materials and are consisted of almost exclusively the elements H, C, N, and O. In comparison to the conventional X-ray inspection system, the neutron radiography is more sensitive with the light elements and, therefore, is more suitable for detecting the materials composed of such elements. Due to the high installation cost, the safety concern and the immobility of the research reactors, the neutron radiography system based on a portable neutron generator is proposed. Since the neutrons generated from a portable neutron generator are mostly the fast neutrons, the system is emphasized on using the fast neutrons for the purpose of conducting the radiography. In order to suppress the influence of X-ray produced by the neutron generator, a combination of a neutron shielding material sandwiched between two identical imaging plates is used as a screen behind the exposed material. An acrylic plate was used as the neutron shielding material as it can attenuate the fast neutrons but remains essentially transparent to the X-ray. A binary XOR operation is then applied on the images obtained by the two imaging plates in order to extract the information regarding the neutron exposure. The raw images obtained confirm that the X-ray really has a large effect and that XOR operation can help enhance the effect of the neutrons. The results also confirm that the fast neutron radiography of the concealed materials composed of H, C, N and O is possible. This can then be useful for detecting the concealed explosive materials composed of such elements.