Performance optimization of scintillator neutron detectors for EMD in CSNS

Chinese Spallation Neutron Source (CSNS) has successfully produced its first neutron beam in 28th August 2017. It has been running steadily from March, 2018. According to the construction plan, the engineering materials diffractometer (EMD) will be installed between 2019–2023. This instrument requires the neutron detectors with the cover area near 3 m² in two 90° neutron diffraction angle positions, the neutron detecting efficiency is better than 40%@1 Å, and the spatial resolution is better than 4 mm×200 mm in horizontal and vertical directions respectively. We have developed a one-dimensional position-sensitive neutron detector based on the oblique ⁶LiF/ZnS(Ag) scintillators, wavelength shifting fibers, and SiPMs (silicon photomultipliers) readout. The inhomogeneity of the neutron detection efficiency between each pixel and each detector module, which caused by the inconsistency of the wave-length shifting fibers in collecting scintillation photons, needs to be mitigated before the installation. A performance optimization experiment of the detector modules was carried out on the BL20 (beam line 20) of CSNS. Using water sample, the neutron beam with Φ5 mm exit hole was dispersed related evenly into the forward space. According to the neutron counts of each pixel of the detector module, the readout electronics threshold of each pixel is adjusted. Compared with the unadjusted detector module, the inhomogeneity of the detection efficiency for the adjusted one has been improved from 69% to 90%. The test result of the diffraction peak of the standard sample Si showed that the adjusted detector module works well.