The very small-angle neutron scattering (VSANS) spectrometer is currently being constructed at the China spallation neutron source (CSNS). The neutron detector plays a key role in meeting the detection requirements of the spectrometer.

This study aims to achieve accurate measurement of neutron diffraction in the small angle scattering mode which requires the position resolution of the neutron detector to be ≤2 mm, and the detection efficiency to be ≥60%@0.4 nm.

A large-area position-sensitive neutron scintillator detector mainly composed of ⁶LiF/ZnS(Ag) scintillation screen, wavelength shift fiber (WLSF), and a silicon photomultiplier (SiPM) was designed and developed to achieve high efficiency and high-resolution real-time detection of thermal neutrons. The optical transmission performance of the 0.5-mm-diameter wavelength shift fiber was investigated in detail. The gain and the thermal noise characteristics of various SiPMs were examined. Finally, a 300 mm×300 mm engineering prototype of the detector was developed and tested by experiments. The detection efficiency was calculated with comparison of the incident neutron counts of the stander ³He tube whilst the detector's position resolution was tested using a boron-doped aluminum plate with a narrow slit bearing the label 'CSNS'.

The neutron beam test results show that the position resolution of the detector is 1.2 mm×1.2 mm and that the neutron detection efficiency is (61.8±0.2)%@0.4 nm.

The high-resolution neutron scintillator detector developed in this study satisfies the engineering design target, and meets the neutron scintillator detector meets the neutron diffraction measurement needs for the VSANS spectrometer of the CSNS.