Position Sensitive Alpha Detector for an Associate Particle Imaging System

Associated Particle Imaging (API) is a nuclear technique that allows for the nondestructive determination of 3D isotopic distributions. The technique is based on the detection of the alpha particles associated with the neutron emitted in the deuterium-tritium (DT) fusion reaction, which provides information regarding the direction and time of the emitted 14 MeV neutron. Inelastic neutron scattering leads to characteristic gamma-ray emission from certain isotopes, for example C-12, that can be correlated with the neutron interaction location. An API system consisting of a sealed-type neutron generator, gamma detectors, and a position-sensitive alpha detector is under development for the nondestructive quantification of carbon distribution in soils. This paper describes the design of the alpha detector, detector response simulations, and first experimental results. The alpha detector consists of a Yttrium Aluminum Perovskite (YAP) scintillator mounted on the inside of a neutron generator tube. The scintillation light propagates through a sapphire window to a position-sensitive photomultiplier tube mounted on the outside. The 16x16 output signals are connected through a resistive network for a 4-corner readout. The four readout channels are amplified, filtered, and then digitized for the calculation of the alpha position. First test results demonstrate that an excellent alpha position resolution, better than the 1 mm FWHM required by the application, can be achieved with this detector design.