Study of High-Energy Gamma-Ray Imaging Detectors for Fast Neutron Analysis

Explosives and drugs have distinctive Carbon, Hydrogen, Oxygen, and Nitrogen contents. In this thesis, we introduce the Fast Neutron Analysis (FNA) technique for explosive and drug inspection. Fast neutrons induce gamma rays (mainly by inelastic scattering) of different energy from different nuclei and the intensity of a certain energy gamma ray represents the intensity of a corresponding nucleus. By imaging the induced gamma rays of different energies by Coded Aperture Imaging (CAI) method, we obtain a mapping of elemental distribution and are therefore able to recognize hidden explosives and drugs. The processes of Neutron penetration and gamma ray production are studied using MCNP-4A code and Coded Aperture Imaging method is briefly introduced. The results have shown that FNA technique when combined with CAI method offers a solution in elemental mapping, and therefore explosive and drug inspection. Great emphasis is given in the detector performance. Energy resolution, spatial resolution, and detection efficiency have been studied in detail. A sodium iodide (Nal