快中子敏感硅微通道板的模拟与设计

Simulation and design of fast neutron sensitivity silicon microchannel plate

兰州大学研制的快中子成像探测器由聚乙烯转换器、铅玻璃微通道板和电荷耦合器件(Charge Coupled Device,CCD)相机组成,为了进一步提高探测器的空间分辨率,计划用硅微通道板(Silicon Microchannel Plate,Si-MCP)作为像探测器中的转换器和倍增器件。采用蒙特卡罗模拟工具包Geant4,建立Si-MCP的模拟模型,并模拟Si-MCP对14 MeV快中子的转换效率和空间分辨率随板厚、倾角、孔径、壁厚的变化规律。通过分析模拟结果,对Si-MCP的几何结构进行优化,最终确定Si-MCP的几何参数。模拟结果显示:转换效率主要随板厚的增加而增加,倾角方向的空间分辨率主要受到板厚和孔道倾斜角度的影响。当Si-MCP的板厚为1 mm,通道倾角为2°,孔径设置为10μm,壁厚设置为10μm时,Si-MCP对14 MeV快中子的转换效率为0.15%,倾角方向的空间分辨率为43μm。采用V型叠加的双层Si-MCP探测系统,对14 MeV快中子的转换效率为0.31%,倾角方向的空间分辨率为43μm。模拟结果将作为设计快中子像探测器中的Si-MCP的参考依据。

[Background]A fast neutron image detector developed by Lanzhou University is composed of polyethylene converter,lead glass microchannel plate and charge coupled device(CCD)camera.In order to further improve the spatial resolution of the detector,a silicon microchannel plate(Si-MCP)is proposed as both converter and multiplier.[Purpose]This study aims to improve the conversion efficiency and spatial resolution of Si-MCP by simulation design.[Methods]First of all,Monte Carlo code Geant4 was employed to build the simulation model of a Si-MCP and neutron source.Then,the conversion efficiency and the spatial resolution of the Si-MCP for 14 MeV fast neutrons in various geometrical configurations were simulated.Finally,geometric structure of Si MCP was optimized,and the geometric parameters of Si MCP were determined by analyzing the simulation results.[Results]The simulation results indicate that the conversion efficiency of the Si-MCP increases with its thickness.The spatial resolution mainly depends on the thickness and bias angle of the plate.When the plate thickness is 1 mm,the micropore diameter is 10μm,the wall thickness is 10μm,and the bias angle is 2°,a conversion efficiency of 0.15%with a spatial resolution of 43μm can be achieved.Double layer Si MCP detection system with V-type superposition structure can be adopted to achieve 0.31%conversion efficiency for 14 MeV fast neutrons.[Conclusions]The calculation results can provide reference for the design of the Si-MCP in fast neutron image detector.