A Gd-based gaseous electron multiplier detector for neutron scattering applications

The optimum configuration of a Gaseous Electron Multiplier (GEM) neutron detector using a CsI–Gd–Kapton–Gd–CsI neutron converter is investigated using Monte-Carlo simulations. Neutrons absorbed in the converter produce secondary electrons that are emitted from the CsI layers. The detector can be assembled from multiple modules where each module consists of the neutron converter, several cascaded GEMs and anode pickup plates on both sides. Position sensitive anodes and localization electronics are then used to detect, timestamp and record the resulting signal. For a single GEM module, the performance can be assessed by estimating the secondary electron (SE) leakage from the converter sandwich. The simulations show that the optimum for a single module, double-sided detector would have a neutron converter composed of 0.1 μm CsI on top of 3 μm Gd plated on each side of a 7.5 μm thick Kapton foil. This detector would have a SE yield of approximately 0.6 SE/neutron and neutron absorption of 60%. Significant enhancements of the SE yield can be obtained for detectors composed of multiple modules with thinner Gd converters. The multi-module design allows for enhanced SE leakage from each converter while maintaining the high neutron absorption efficiency of thicker converters and dividing the detector count rate among multiple sets of decoding electronics.