Development Of ~3He Tube Detector For Csns Very Small Angle Neutron Scattering Spectrometer

Due to its unique physical properties,neutron is an ideal probe for studying molecular-scale microstructure and microscopic dynamics processes,and the China Spallation Neutron Source(CSNS)is a key large scientific device in China,providing a platform for basic research and high-tech R&D in materials science,new energy,medical and pharmaceuticals,and key electronic devices.The Very Small Angle Neutron Scattering Spectrometer(VSANS)is a supplement to the Small Angle Scattering Spectrometer(SANS)for material characterization,covering three scales from 1 nm to 1000 nm.It has a wide range of applications in the structural study of soft and condensed matter,including colloids,macromolecules,and biomolecules,and has a wide range of industrial applications.The detector system is the core of the spectrometer and the focus of this paper.According to the physical design,VSANS has two modes of operation:Small-Angle-Neutron-Scattering mode and Very-Small-Angle-Neutron-Scattering mode,using ~3He tube detectors for the SANS mode and High-resolution GEM detectors for VSANS mode.This paper is based on the VSANS detector project~2,among with research team carries out the development of ~3He detector system to solve the key technical problems in the engineering construction process.In order to realize the engineering application of the detector,this paper constructs the ~3He tube model and scattering chamber model based on Geant4 simulation software,studies the detection efficiency of ~3He tube for different wavelengths of neutrons under different air pressure and the scattering of neutrons by air,and verifies the necessity of using vacuum to reduce the neutron noise and improve the quality of scattering experiments.Based on the physical simulation of the detector,a high pressure position sensitive ~3He tube with 8 mm tube diameter and 20 atm filling pressure from LND was selected,and the mechanical design of the detector was optimized together with the team;the detector,electronics,and data acquisition system were jointly tested.Developed a prototype detector,built a set of detector module batch fabrication platform,completed the fabrication of detector module,and tested the core performance of the detector at CSNS 20 beam line.The detector was scaled using a 3mm thick boron aluminum alloy with a slit width of 2 mm and a spacing of 100 mm.The resolution of the detector was 7.52 mm(±0.16 mm),which was better than the design index of 8 mm.The detector module meets all performance requirements of the VSANS.The work in this paper provides a powerful tool for VSANS system and promotes the process of independently developing the technology related to neutron detector system.