Simulation of Concept for Compact Single Volume Neutron Scatter Camera for Nuclear Safeguard Applications

A fast neutron scatter camera is sought for the purposes of localizing neutron emitting sources for nuclear safeguards and security purposes. Localization of a neutron source entails determining the general direction of a source in 3-D space rather than imaging or identifying the type of source. Fast neutron cameras which have been developed rely on multiple detector volumes and make use of neutron time of flight measurements. These designs, though effective in localizing the source direction, relies on a large amount of detection and electrical equipment thus increasing the size of the system to unwieldy dimensions for some deployment scenarios. This project seeks to develop a compact scatter camera several time smaller than systems relying on multiple detector volumes. In this design, neutrons will interact twice in the same scintillator detector volume, allowing for a more compact system. Using picosecond electrical pulse timing, the electronics employed will be able to distinguish between scintillation light pulses generated by the same neutron on separate sides of the detector volume. Knowing the approximate positions of scatters from a single neutron and the energy deposited in each scatter, one can back project a “cone of uncertainty” where possible source locations may be. The zone of overlap for all the cones generated in a set measurement time is used to generate a vector pointing toward the direction of the source. A MCNPX-Polimi model of a cube-shaped scintillator volume was developed. The localization of interaction position inside the detector volume is determined by ratios of light intensity detected at photomultiplier tubes mounted on each of the six faces of the detector. An algorithm was developed in MATLAB to localize the source in simulation space based on the interaction positions and energies deposited using light intensity data from six photomultiplier tubes. Detector efficiency, imaging resolution, and reconstruction of the source neutron energies are reported for the design.