A large-area two-dimensional scintillator detector with a wavelength-shifting fibre readout for a time-of-flight single-crystal neutron diffractometer

A two-dimensional scintillator-based neutron detector that has a neutron-sensitive area of 256×256 mm2 with a pixel size of 4 mm was developed. The detector was designed to be compact and modular with the smallest dead area for the SENJU time-of-flight Laue single-crystal diffractometer to be constructed in the Materials and Life Science Experimental Facility at the Japanese Proton Accelerator Research Complex. The detector employed wavelength-shifting (WLS) fibres to collect scintillation light generated in a neutron-sensitive scintillator. The 64 WLS fibres with a diameter of 1 mm were regularly spaced at a pitch of 4 mm both in the x and y directions to produce a detector with a large neutron-sensitive area and a small number of electronics channels. Two ZnS/10B2O3 scintillator screens with an optimised scintillator thickness sandwiched the cross-arranged WLS fibre arrays to ensure a high detection efficiency for thermal neutrons. The prototype detector exhibited a detector efficiency of 40±1%(mean±SD) for 1.6 Å neutrons and a 60Co gamma-ray sensitivity of 6.0±0.1×10−6, which fulfilled the required detector specifications for SENJU.