The Research Of The Scintillator Neutron Detector Based On The Anger-camera Principle

The single crystal neutron diffraction spectrometer designed by Chinese spallation neutron source adopts Laue diffraction technique,uses time-of-flight to determine wavelength resolution,and has a high position sensitive neutron detector,which can detect all the diffraction points in the sample in a very short time,which provides a strong support for the study of molecular crystallography.The scintillator detector developed in the previous stage of the spallation neutron source detector group is composed of scintillator,wave-shifted optical fiber and multi-anode photomultiplier tube(Multi-anode Photomultiplier Tube,MAPMT),which can be used for large-scale neutron detection.It has 4mm × 4mm position resolution and thermal neutron detection efficiency which is better than 40% thermal neutron detection efficiency.However,as a commonly used photoelectric conversion device,MAPMT has great non-uniformity of unit gain,and is easily disturbed by electromagnetic field.At the same time,it has large volume and high-power consumption.In recent years,silicon photomultiplier tube(the Silicon Photon Multiplier tube,Si PM)has developed rapidly,it has excellent single-pulse photon resolution performance,and because it does not produce large gain fluctuation or noise like avalanche diodes,the singlephoton resolution performance is also better than other photomultiplier tubes.In addition,it also has the advantages of sturdiness,compact size and large area splicing,which makes it an ideal choice in the field of optoelectronics detection.Because of its advantages such as low working voltage,not affected by external electromagnetic environment and low cost,Si PM has become an ideal substitute in the fields of high energy physics,nuclear medical imaging,life sciences,quantum communication and lidar,providing strong support for the development of these fields.In this paper,a position-sensitive scintillator neutron detector based on Anger-Camera principle is developed.its main structure is as follows: 6Li F/Zn S(Ag)scintillation screen is used as neutron sensitive probe,and combined with silicon photomultiplier tube array and composite compression circuit,efficient optical readout and non-redundant data processing are realized.at the same time,high position resolution is achieved by charge distribution method.This paper first describes the physical design of the scintillator neutron detector of Anger-Camera,and studies the performance of the key devices of the detector,including the light yield of the scintillator of the neutron sensitive probe 6Li F/Zn S(Ag),the detection efficiency,the thickness and coupling mode of the air photoconductor,the position reconstruction ability of the Si PM array and supporting electronics,etc.By using the Monte Carlo software GEANT4,we simulate and optimize the photoconductive geometric parameters of the key devices of the detector,and introduce the modulation transfer function MTF to evaluate the position resolution of the detector.The results show that when the photoconductive thickness of the neutron detector is 5mm,the detector can achieve the best position resolution.Finally,according to the simulation results,the prototype of the neutron detector is successfully fabricated,and the neutron beam test is carried out in the BL20 neutron testing laboratory in the CSNS target station.The position resolution of the detector can be determined under the condition of different thickness and material photoconductivity,and the air photoconductor with 5mm thickness can achieve the detector position resolution of 0.6mm,while avoiding the problem of large neutron scattering cross section of traditional photoconductivity.It is found that the highest counting rate of the detector system is about 23-25 KHZ.The Bragg edge imaging capability of the detector is preliminarily studied by using316 L stainless steel samples.the results show that the detector can be used for Bragg edge transmission imaging in the future and is expected to be applied after the completion of the neutron spectrometer project.With the construction and operation of spallation neutron source,national advanced experimental reactor and Mian yang reactor in China,a large number of neutron spectrometers will be built one after another,so there is a very urgent technical demand for neutron detectors with higher detection efficiency and high position sensitivity,especially for the new detection technology that can replace 3He detectors.After successful research and design,the new scintillator neutron detector can not only meet the urgent needs of neutron scattering experiments in our country,but also greatly improve the level of neutron detection technology in our country.In addition,the batch products of the detector can provide domestic advanced scintillator neutron sensors for many advanced neutron spectrometer detection systems in China,so as to provide support for basic scientific research more effectively.