Achievable position resolution of an alpha detector with continuous spatial response for use in associated particle imaging

Abstract

Deuterium-Tritium (D-T) neutron generators have seen increasing use as high energy neutron sources tor active, nondestructive assay in arms control, treaty verification, and nuclear and homeland security applications. The D-T reaction produces a 3.5 MeV alpha and a 14.1 MeV neutron that travel in opposite directions, which facilitates transmission and stimulated fission tomography to reconstruct images of inspection objects and closed containers to infer isotopic and geometric information. However, the accuracy of this information is controlled by image quality, which is directly dependent on the performance of the detectors used to detect the neutron and its associated alpha. This work presents improved spatial performance for an associated particle detector by using a thin sapphire window as the D-T generators optical-vacuum medium and reading a position sensitive photosensor with a continuous spatial response. Measurements of achievable position resolution were performed with a custom vacuum chamber and flange for a 2 mm thick sapphire window that mimicked the neutron generators alpha detector interface. Measurements were used to validate detailed, light transport simulations that were then used to optimize light sharing over the multi-anode PMT by parameterizing the thickness of the sapphire window. A position resolution <;0.5 mm was demonstrated, which is a factor of 3 times improvement over what has previously been demonstrated by associated particle detector designs that pixelate monolithic scintillators with a slotted light guide. This gain in position resolution showed good agreement with light transport simulations. Achievable position resolution is shown for different sapphire window thicknesses and the benefits of this designs implementation into D-T neutron generators are presented.