Directional Pair-Production Spectrometer Design For Airborne Stand-Off Detection of Special Nuclear Material

The purposes of this research are to experimentally and theoretically prove the concept of a directional pair-production spectrometer to detect and locate the tailings that are created when making Special Nuclear Material (SNM) at stand-off distances from a remotely piloted vehicle (RPV). A directional pair-production spectrometer uses the information garnered from the high energy gamma rays emitted by these SNM manufacturing tailings to perform pair-production spectroscopy and identify the isotope of interest. Through simultaneous operation as a Compton camera, the detection system will be able to measure rudimentary directional information from the medium energy gamma decays. The detector used for this research is constructed of four LaBr3 detectors and operated in coincidence to allow for the reduction of background. The directional efficiency of the detector in measuring the radioactive decay of a 6.7 Ci Co-60 source is validated with a Geant4 simulation. The simulation is used to predict the directional efficiency of a detector system using six detector elements and the pair-production spectrum that would be seen when measuring a higher energy gamma ray source.