Development Of Position-sensitive Thermal Neutron Detector Based On SiPM Array Readout

Neutron scattering technology,as an important means to study the structure of matter,is complementary to X-ray diffraction technology.Neutron scattering technology plays an irreplaceable role in determining molecular and crystal structures in biology,condensed matter physics and polymer chemistry.The establishment of the China Spallation Neutron Source(CSNS)has laid the foundation for the development and application of neutron scattering technology.With the improvement of the new generation of neutron science devices,the performance of neutron detectors is even more challenged.Most traditional neutron scattering spectrometers use 3He gas detectors,which can achieve large area and high detection efficiency,and have a good n/γ suppression ratio.However,its position resolution is difficult to be better than 5mm and its detection efficiency is not uniform when large-area arrays are used in splicing.In recent years,scintillator detectors based on high-performance neutron-sensitive scintillators and novel photoelectric readout devices have developed rapidly.With the advantages of high detection efficiency,high position resolution,and wavelength resolution,they have achieved large-area applications in many neutron devices.Domestic engineering high-performance neutron detectors have been heavily dependent on imports for a long time,subject to the technological blockade of developed countries,and the research on high-position resolution scintillator detectors is still blank.As a new type of optical readout device,the application of SiPM in the field of neutron detection is in its infancy.And there are still no relevant reports on its large-area application in the world.It solves the problems of high power consumption,large volume,high price,uneven gain response,and difficulty in working in a strong magnetic field environment for traditional photomultipliers.Its application in the field of neutron detection will be the general trend.This paper presents a position sensitive thermal neutron detector based on SiPM array readout,which has high position resolution,small dead zone and large area splicing.The detector adopts 6LiF/Zn S as the neutron sensitive probe,the high-performance and low-cost SiPM array combined with the composite compression circuit as the optical readout,and the charge distribution method is used to achieve high position resolution in position reconstruction.Firstly,this paper designs the whole detector.The structure of position-sensitive thermal neutron detector composed of 6LiF/Zn S scintillator,BK7 photoconductor,SiPM array and compression circuit was selected as the research object.Geant4 Monte Carlo simulation was used to optimize the thick of the detector optical guide and other parameters.MTF was used to evaluate the position resolution with different thick optical guides.The results show that the detector can achieve a position resolution of about 0.34 mm when a 6LiF/Zn S scintillation screen with a 5 mm thick BK7 photoconductor is used.Finally,according to the simulation results,a detector prototype was fabricated,and experimental research was carried out on the BL20 of CSNS.The maximum count rate and position resolution of the detector are respectively studied,and the results show that the detector has a maximum count rate of about 7.5 k Hz and a position resolution of about 0.7 mm,which indicates the detector has sub millimeter position resolution.At the same time,Bragg edge imaging was studied on 316 L stainless steel samples,and energy selective imaging experiments were performed on iron and copper samples.The results show that the detector has good capacities of Bragg edge imaging and energy selective imaging,and is expected to be applied to the actual neutron spectrometer project.With the opening of China Spallation Neutron Source,China Advanced Research Reactor and Mianyang Reactor,a large number of neutron spectrometers will be built one after another.There is an urgent need for a new detection technology for 3He detectors.Therefore,the research on this new type of scintillator neutron detector can not only meet the urgent needs of my country in the field of neutron scattering experiments,but also will be of great significance to improve the level of neutron detection technology in my country.After the success of this research,mass production can be formed to provide domestic high-performance neutron detectors for many advanced neutron scattering experimental platforms in China.