Nuclear physics research has a need for fast neutron imaging of objects that are several mean-free-paths thick. For the associated particle imaging technique to work, sufficiently fast and high spatial resolution alpha-particle imaging is required. Alpha particles are generated in the fusion reaction that creates the neutron as well. By tracking the location and timestamp of these alpha particle detection events, one has information on the initial direction and creation time of that neutron. While conventional in-vacuum scintillators and air-side position-sensitive light sensors are up to the task, getting the light through the vacuum window without loss of spatial resolution remains a key challenge. This vacuum barrier must withstand high temperature vacuum bake, be made of materials compatible with welding to the neutron generator target assembly and maintain vacuum integrity for a workable neutron generator. Using fiberoptic faceplates that present a zero optical thickness approach and maintain spatial resolution is a demonstrated approach, but the component yield has been small and there is insufficient commercial interest due to the size of the current market. Initial Phase I development will demonstrate proof of concept success for the proposed application, Custom Fiber Optic plate (FOP) windows will be fabricatedutilizing a fiber packing structure in a half-hex methodology and bonded to a mating alloy flange that will closely match the FOPs coefficient of thermal expansion (CTE). Furthermore, this approach, along with developing a Hot Isostatic Pressing process to frit seal the matching CTE alloy flanges to a fiberoptic plate will help mitigate fracturing of frit seals in the final assembly. Stronger bonding from HIP fusing and closer matching CTE will allow the assembly to be welded into a stainless-steel housing and baked out at 350 C for an extended (>1 day) period without the loss of the vacuum. A successful effort to develop a hermetic glass-metal seal for a 50-mm or greater diameter fiber-optic faceplate that can withstand the rigors of neutron generator fabrication helps to advance the associated particle imaging (API) D-T neutron generator state-of-the-art. The development of portable, high-output API D-T neutron generators can make neutron imaging a viable diagnostic tool for applications that require imaging of thick, dense objects with high-Z materials for which X-ray imaging is infeasible.
