A prototype, high-efficiency, position sensitive neutron detector for the proposed neutron spin rotation experiment at the SNS

We are developing a position sensitive ($\sim$ 1 cm resolution) neutron detector with nearly 100\% efficiency for use at the high flux ($> 5 \times 10^{10}$ neutrons/sec) pulsed beam at the Oak Ridge Spallation Neutron Source (SNS). The prototype detector is important for transmission experiments such as the proposed parity-violating neutron spin rotation in hydrogen measurement. The detector concept integrates the segmented $^3$He ionization chamber designed for the preliminary spin-rotation in helium experiment\footnote{S.D. Penn {\em et al.}, Nucl. Instr. and Meth. {\bf 457} 332 (2001)} and the position sensitive, charged particle collection technology currently being developed at ORNL for low-efficiency beam-transmission monitors for the SNS\footnote{C.L. Britton et al., IEEE Trans. Nucl. Sci., 51, 1016 (2004).}. Neutron absorption on $^3$He produces $^1$H and $^3$H that pass through a wire grid producing an $e^-$ shower detected in current mode by wire strips mounted on a substrate. For 100\% efficiency, regions are created with a series of high-voltage plates, grids, and wire strips each strategically located along the beam axis. Analysis over several regions with alternating wire strip orientation provides a two-dimensional beam profile. We will present our prototype model and test results.