Investigation of Time and Position Resolved Alpha Transducers for Multi-Modal Imaging with a D-T Neutron Generator

Deuterium-Tritium (D-T) neutron generators have been used as an active interrogation source for associated particle imaging (API) techniques. The D-T reaction yields a 14.1 MeV neutron and a 3.5 MeV alpha (or assoicated) particle, projected nearly back-to-back. The kinetics of the reaction allow the direction and initial time of the neutron to be determined utilizing position sensitive detectors for both the alpha and neutron. This information facilitates multi-modal fast neutron imaging of inspection objects and closed containers to infer the geometry within them and the presence of special nuclear material (SNM). Since position and time of interaction of the alpha and neutron within their respective detection media are required to form these images, improved certainty in the direction and timestamp of the both provides improved imaging performance.

This dissertation presents work performed to understand performance limits of a first-generation design associated particle detector (APD) for a specific prototype imaging system developed by the Nuclear Materials Detection and Characterization Group at Oak Ridge National Laboratory. The performance of the first-generation design was first studied through measurements, analytical timing models, and detailed Monte-Carlo timing simulations. Implications on the influence of certain factors on next generations designs were taken from this study. Clear pathways for improved detector performance were identified through the engineering and implementation of new light interfaces and new detector technology. With these improvements in place, three next-generation prototype APD designs were developed with excellent timing performance and optimum trade-offs in position resolution.