First studies of electron transport along small gas gaps of novel foil radiation converters for fast-neutron detectors

TL;DR

This study investigates electron transport in narrow gas gaps of novel foil-based fast-neutron detectors, demonstrating high efficiency in electron collection and implications for detector performance in neutron detection applications.

Contribution

It provides the first systematic analysis of electron transport in small gas gaps of polymer foil converters, combining experimental measurements and simulations.

Findings

95% electron collection efficiency for 6 mm drift length

Lower efficiency (~7%) for 2.5 MeV neutrons with specific converter design

Mechanical and electrical flaws reduce efficiency in 10 mm converters

Abstract

Novel high efficiency fast-neutron detectors were suggested for fan-beam tomography applications. They combine multi-layer polymer converters in gas medium, coupled to thick gaseous electron multipliers (THGEM). In this work we discuss the results of a systematic study of the electron transport inside a narrow gap between successive converter foils, which affects the performance of the detector, both in terms of detection efficiency and localization properties. The efficiency of transporting ionization electrons was measured along a 0.6 mm wide gas gap in 6 and 10 mm wide polymer converters Computer simulations provided conceptual understanding of the observations. For a drift lengths of 6 mm electrons were efficiently transported along the narrow gas gap, with minimal diffusion-induced losses; an average collection efficiency of 95% was achieved for the ionization electrons induced by a primary electron of a few keV initial energy. The 10 mm height converter yielded considerably lower efficiency due to electrical and mechanical flaws of the converter foils. The results indicate that detection efficiencies of around 7% can be expected for 2.5 MeV neutrons with 300 foils converters, of 6 mm height, 0.4 mm thick foils and 0.6 mm gas gap.