Position-dependent neutron detection efficiency loss in 3He gas proportional counters

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Accelerators, spectrometers, detectors and associated equipment, 2020-12, Vol.982, p.164574, Article 164574
• Main Authors: Peplowski, Patrick N., Yokley, Zachary W., Liebel, Madison, Cheng, Shuo, Elphic, Richard C., Hoogerheide, Shannon F., Lawrence, David J., Nico, Jeffrey S.
• Format: Article
• Language: English
• Subjects: 3He gas proportional counter; Neutron detection; Neutron efficiency
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/j.nima.2020.164574

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%.