Study On Fast Neutrons Spectroscopy Based On Micro-pattern Gas Detector

The neutron energy spectrum is a unique characteristic of the neutron source and can be used to identify the source term.Obtaining accurate neutron energy spectrum plays an important role in research fields such as nuclear reactors,radiation protection,and nuclear physics.Since neutrons are uncharged and cannot be directly measured,this article focuses on neutron spectrum detection and simulation,unfolding the neutron spectrum program,and neutron detection experiment.The work on neutron spectrum is mainly divided into the following three Part:1.This work uses high-density polyethylene as the neutron conversion material,and uses MCNPX and Geant4 software to simulate the polyethylene conversion structure.(1)Simulating the thickness of a single layer of polyethylene,the detection efficiency will increase as the thickness of the polyethylene increases first and then become saturated.The thickness of the polyethylene corresponding to this saturated state is the maximum value of the neutron source.Excellent thickness.(2)The single-layer detection efficiency is low.In order to improve the detection efficiency,the multi-layer polyethylene structure is explored.The optimal thickness polyethylene and 500?m air gap are used as a unit.When the conversion unit reaches 200 layers,the detection efficiency is better than that of a single layer.Increase 5 times when layering.Therefore,the multilayer polyethylene conversion structure can effectively improve the detection efficiency.(3)Since the interaction between neutrons and polyethylene will reduce energy,the decreasing structure is more conducive to improving the efficiency and accuracy of neutron detection.Therefore,the simulation is carried out for two different decreasing structures,the first one: decreasing according to the accuracy of the existing 3D printing technology of 100?m.The second type: Use energy cutoff to find the number of layers that reduce the energy of 1Me V under the optimal thickness.By comparison,the detection efficiency of the second structure is 20% higher than that of the first one.2.Using Matlab software,two kinds of the neutron spectrum unfolding program,GRAVEL and MLEM were written,the response matrix and recoil proton spectrum of the two structures were extracted,and unfolding the neutron spectrum program was used to solve the incident neutron spectrum.The resolution of the two structures is about0.6% higher than that of the first structure.The MLEM algorithm is about0.4% better than the GRAVEL algorithm.At the same time,the relationship between the energy resolution of the gas detector and the resolution accuracy is studied.The results show that when the energy resolution of the microstructure gas detector is better than 30%,the resolution accuracy of the fast neutron can meet the actual application requirements.3.Simulation: It is proved that the micro-pattern gas detector can be applied to fast neutron detection,and can use the inversion algorithm to realize the energy spectrum reconstruction of the incident neutron source.In terms of experiment: Build the Triple GEM detector system and make the polyethylene conversion structure,and test the Triple GEM detector system.The modeling and unfolding spectrum algorithm in this article provides a new method for the future application of the micro-pattern gas detector fast neutron detection system to the unknown fast neutron source to reconstruct the energy spectrum to achieve the purpose of identifying the source item.