Position-dependent neutron detection efficiency loss in 3He gas proportional counters
P. N. Peplowski, Zachary W. Yokley, Madison Liebel, Shuo Cheng, R. C. Elphic, Shannon Fogwell Hoogerheide, D. J. Lawrence, J. S. Nico
Abstract
The position-dependent neutron detection response of a 3He gas proportional counter (GPC) was characterized using a collimated (3-mm-wide), monoenergetic (0.05 eV) neutron beam. For neutrons incident on the GPC near the ends of the active region, the neutron capture peak broadens and the position shifts to lower pulse-height channels. This “edge effect” is due to lower gas gain within the decreasing electric field near the end of the active volume. For simple peak-region-summing analyses, the consequence is a loss of events that is equivalent to a 13% reduction in the active area of our GPC. Summing over all events above the triton wall-effect feature significantly reduces this efficiency loss. Whole-sensor illumination measurements simulated with Geant4 required a correction for the edge effect to accurately reproduce the shape and amplitude of the measurements. Once these corrections were applied, the Geant4 models reproduce the whole-sensor count rates to within 10%.