Abstract of the ThesisModeling the tagged neutron technique for the identification of Unexploded OrdnancebyYuanyuan WangMaster of ScienceinMechanical EngineeringStony Brook University2010This research is a collaboration between the Department of Mechanical Engineering at Stony Brook University (PI: Yu Zhou) and the Department of Environmental Sciences at Brookhaven National Laboratory (Collaborator: Sudeep Mitra). The ultimate goal of this research is to develop the associated particle neutron time-of-flight (APTOF)-based UXO detection and discrimination technique and construct a prototype compact and portable neutron interrogation probe that will search for UXO in a target volume, locate targets in three dimensions, and identify the major elemental constituents of each target for discrimination. This project focuses on feasibility study, mainly consisting of proof-of-concept, experimentally modeling and data analysis. An associated particle time-of-flight (APTOF) system has been developed by using the GEANT4 4.9.2.p01 toolkit.In this study, significant efforts have been made to develop a neutron interrogation UXO sensing system model based on GEANT4 simulation Toolkit (G4). This simulation includes modeling of the neutron beam, alpha beam sources and collimation, the samples, the neutron interaction within the samples, the emission of characteristic gammas, and the detection of these gammas, as well as the detection of the alpha particles. Continuous coincident neutron flux and alpha particles were generated from D-T fusion reaction model and were captured by physical and geometric condition strict detectors in G4. A fast, time-saving associated particle imaging algorithm has been developed by correlating the time and direction of alpha particles and emission of gamma rays from fast neutrons, thus making the system capable of multi-dimensional imaging, as well as sensing elements such as C, N, O, Si, Al, Ti, etc Optimized time window has also been employed due to variable soil background can severely affect the signal-to-noise ratio for elemental measurement. From the images and spectrums we can accurately reconstruct the shape, location and components of objects of interest that are hidden from view. Useful signals from an UXO buried to about 20cm in the sub-surface can be measured. Results from the simulation experiments demonstrate that GEANT4 is an effective simulation platform to develop the APTOF sensing system and to facilitate future development and optimization. In particular it can model the geometry of the system for optimum neutron reactions with nuclei in the sample, capture of gamma rays and alpha particles, as well as gamma energy deposition and 2D and 3D imaging.