A new pad-based neutron detector for stereo coded-aperture thermal neutron imaging

A new generation of coded aperture neutron imagers is being developed at Brookhaven National Laboratory. The detector of the camera is a position-sensitive thermal neutron chamber. The new device is a ³He-filled ionization chamber, which uses only anode and cathode planes. The anode is composed of an array of individual pads. The charge is collected on each of the individual 5×5 mm² anode pads, (48×48 in total, corresponding to 24×24 cm² sensitive area) and read out by application specific integrated circuits. The new design has several advantages for the coded-aperture applications in the field, compared to the previous generation of wire-grid based neutron detectors. Among these are its rugged design, lighter weight and use of non-flammable stopping gas. The pad-based readout is event by event, thus capable for high count rates, and also to perform data analysis and imaging on an event-by-event basis. The spatial resolution of the detector can be better than the pixel size by using charge sharing between adjacent pads. In this paper we report on the development and performance of the new, prototype pad-based neutron camera, and present the first stereoscopic coded aperture images of thermalized neutron sources.