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提出了一种由聚乙烯(Polyethylene,PE)转换器、微通道板(Microchannel Plate,MCP)电子增强器和CCD(Charge-Coupled Device)相机组成的快中子照相像探测器新方案。采用Geant4软件模拟研究了14.5 Me V快中子入射在PE转换器上的出射质子产额、能谱随PE厚度的变化规律,确定了PE转换器的厚度范围和转换效率等重要参数。模拟结果显示,PE转换器的厚度应该选择在2.5 mm左右,此时的转换效率约为0.37%。采用Geant4软件模拟了14.5 Me V快中子入射在PE转换器的质子输运和质子在MCP中电子的产生和倍增过程,给出了MCP输出的电子束斑图像。模拟结果显示,由PE和MCP组成的转换器系统能将入射的快中子转换成电子束斑点阵信息,各电子束斑之间的界限清晰,单孔电子束斑直径略大于MCP孔径,即电子束斑点阵像素可以达到MCP孔径量级。
A new fast neutron imaging detector consisting of polyethylene (PE) converter, Microchannel Plate (MCP) electronic intensifier and CCD (Charge-Coupled Device) camera is proposed. The proton yield of 14.5 Me V fast neutron incident on the PE converter was simulated by Geant4 software. The energy spectrum of the PE converter was determined by the variation law of the PE thickness. The parameters such as the thickness range and the conversion efficiency of the PE converter were determined. The simulation results show that the thickness of the PE converter should be about 2.5 mm, and the conversion efficiency at this time is about 0.37%. Geant4 software was used to simulate the proton transport of 14.5 MeV fast neutron incident on the PE converter and the generation and multiplication of protons in the MCP. The electron beam spot image of the MCP output was given. The simulation results show that the converter system consisting of PE and MCP can convert incident fast neutrons into electron beam spot array information. The boundary between electron beam spots is clear. The diameter of single hole electron beam spot is slightly larger than the MCP aperture, that is, Electron beam spot array pixels can reach the order of MCP aperture.