Optimized Design and Experimental Validation of a GEM-Based Thermal Neutron Detector

The increasing demand for high-flux neutron detection, driven by next-generation neutron sources, necessitates alternatives to conventional ³He proportional counters, which are limited by space charge effects. This paper presents the development and experimental validation of a thermal neutron detector based on Gas Electron Multiplier (GEM) technology. Key detector parameters were systematically optimized using Monte Carlo simulations (Geant4, Garfield++, SRIM). An Ar/CO₂ mixture with Ar>90% was selected as the working gas, an approximately 1 μm thick ⁶LiF coating was employed as the neutron conversion coating, and the electric field settings were optimized to E_Drift≈150 V/cm, V_GEM≈400 V, and E_Induction>1.0 kV/cm. A prototype detector featuring a two-dimensional readout structure with an active area of 44 mm×44 mm was fabricated based on these optimized parameters. Preliminary performance tests conducted in a thermal neutron field demonstrated that the detector achieves measurement uniformity comparable to that of a ³He proportional counter, while providing millimeter-level geometric resolution in a single measurement. The counting rates in the “X” and “Y” directions are in good agreement with the theoretical values, laying a solid foundation for subsequent measurement applications under high-flux neutron beams.