Development Of Fast Neutron Detector For Atmospheric Neutron Irradiation Spectrometer

Atmospheric neutrons can induce the single event effect of electronic devices,which may lead to the failure of electronic equipment working on the earth’s surface and space environment.This will cause detriment to people’s manufacture and life,including in aviation,communication,scientific research and other aspects.By using high flux neutron beam to irradiate electronic equipment,its anti-irradiation performance and fault tolerance of single event effect can be tested quickly.In recent years,the international neutron sources have set up a special neutron irradiation beam line for these"accelerated test"research.CSNS plans to build the atmospheric neutron irradiation spectrometer,which will fill the gap of the atmospheric neutron irradiation environment in China and provide an international leading atmospheric neutron irradiation test platform for users.In order to provide normalized parameters for experiment and improve the accuracy of test,neutron spectrometer generally needs beam monitor to monitor the change of neutron flux in real time.According to the characteristics and application of the atmospheric neutron irradiation spectrometer,the beam monitor should also have two-dimensional spatial resolution.Because the GEM gas detector has high spatial resolution,high counting rate and fast time response.Therefore,it is widely used in various beam monitors.One of the beam monitors applied in CSNS spectrometer is a thermal neutron beam monitor based on boron-coated GEM detector.At present,the monitor has been running stably for three years and achieved good results.Referring to the development experience of boron-coated GEM thermal neutron monitor,GEM fast neutron detector for fast neutron beam monitoring can be developed based on nuclear fission or nuclear recoil method.In this paper,the fast neutron detector based on GEM was studied by simulation and experiment.The physical process of the detector was simulated by Geant4,and the set of structural optimization scheme suitable for fast neutron detector was obtained.The detector structural parameters such as 2 mm polyethylene fast neutron conversion layer,200μm stopping layer,4 mm working gas and gas ratio（90%Ar+10%CO₂）were determined.Under this structure,the detector has detection efficiency more than 0.2‰for 7 Me V、10Me V and 14 Me V fast neutrons,and it can ensure the sufficient energy deposition of secondary particles in the gas,good n/γsignal-to-noise ratio and good spatial resolution.In this paper,the fabrication technology of the key devices of fast neutron detector was studied,and a prototype of fast neutron detector was completed.The performance of detector was tested by neutron beam.The test results show that the detector has good fast neutron detection ability,and can carry out two-dimensional imaging detection of neutron beam profile,the spatial resolution of the detector is 3 mm,which can meet the beam monitoring requirements of atmospheric neutron irradiation spectrometer.