Year
2014
Abstract
The detection and identification of fissile Special Nuclear Materials (SNM) has become of great concern. This research focused on a computational design of the “Transport Simulation and Validation of a Synthetic Aperture SNM Detection System” (T-SADS System). A time phased radiation signal capture methodology yields an optimum detection window in order to capture identifying signatures from a moving SNM source passing in close proximity to the SADS. The synthetic aperture design is composed of a series of deployed neutron-photon detector array (NPDA) modules that have been evaluated and optimized. A time phased radiation signal capture procedure for each NPDA, cascading from one to the next, enables an expanded detection window with minimal background accumulation. Detailed 3-D computational transport methods were applied utilizing forward and adjoint deterministic Discrete Ordinate (Sn) transport with the PENTRAN code system coupled with Monte Carlo transport simulations using MCNP5. This paper focuses on the neutron detection capabilities of the T- SADS System, and the methodology behind the computational assessment of the T-SADS moderated neutron detection blocks. Deterministic adjoint transport calculations were performed in order to determine the importance of neutrons, efficiency, and relative to the Field of View (FOV) of the detector system. Background contributions assumed to appear from surrounding sources, cosmic background, and ground scatter were established to determine a minimum Currie-limit necessary to achieve a 95% Probability of Detection and a 5% Probability of False Alarm. Results confirmed the T-SADS system’s ability to detect neutron signatures of SNM placed in a car trunk moving at highway speeds, even under realistic neutron background considerations