Highly efficient GEM-based neutron detector for China Spallation Neutron Source

Many new instruments at China Spallation Neutron Source (CSNS) require 3He-free neutron detectors with high counting rate capability to match the high neutron flux provided. The GEM(Gas Electron Multiplier)-based neutron detector is one of few detectors that can operate under direct irradiation from a neutron beam. A prototype detector was constructed using 10 GEM foils of 200 mm × 200 mm. To improve the detection efficiency, eight of the GEM foils and two cathodes were coated with enriched boron (96% 10B). To investigate its basic characteristics, several neutron beam tests were carried out at CSNS and the China Mianyang Research Reactor (CMRR). The spatial resolution of the GEM-based neutron detector was below 2.94 ± 0.01 mm (FWHM). Using monoenergetic neutrons at a wavelength of 4.9 A, the detection efficiency was 54 ± 2%, consistent with the efficiency of 52% given by a Geant4 simulation. The wavelength spectrum measured with this detector using the TOF(Time Of Flight) approach at CSNS agreed well with that measured using a 3He tube. The results show that the GEM-based neutron detector is an ideal candidate to measure the direct neutron beam. Its overall detection efficiency is close to that of conventional 3He neutron detectors.