基于Triple GEM结构的高探测效率快中子成像谱仪研究

At present, the measurement of fast neutron based on MPGD (Micro-pattern Gas Detector) structure has some weaknesses, such as low accuracy and efficiency. This project is proposed to carry out a fundamental research on the spectrometer detection principle and techniques of fast neutron based on a novel multi-layers polyethylene converter structure. The Triple GEM detector, which has some excellent performances and couples with the multi-layers polyethylene fast neutron converter module processed by 3D printing technology, will be used in this project. In theory, the optimal design parameters of the fast neutron detection spectrometer and the fast neuron unfolding spectrum algorithm which applicable to the micro-pattern gas detector will be investigated. In experiment, the preliminary construction of the fast neutron detection based on the multi-layers converter structure，the effect of the distribution of fast neutron energy spectra on the unfolding spectral accuracy together with the function of detection efficiency and also the influence of the metallized polyethylene conversion structure on fast neutron imaging will be studied. The 3D printing technology will be employed in the Micro-pattern Gas Detector to hopefully decrease the effect of internal electric field distortion caused the conversion layer surface roughness. Furthermore, the data readout with multi-channels pixel based on PXI bus, requirements of the neutron beam monitoring and industrial inspection applications，such as rapid diagnostic, can be responded. Therefore, this project is expected to use a simple and relatively efficient fast neutron detection scheme to improve detection efficiency and gain the purpose of fast neutron imaging. As a consequence, this project provides both theory basis and technology foundation for a fast neutron imaging spectral instrument which has a reliable performance.

针对基于微模式气体探测器结构的快中子测量准确性和效率不高的基本现状，本项目拟开展一种新型多层聚乙烯转化结构的快中子探测谱仪原理与技术的基础研究。提出将3D打印技术加工的多层聚乙烯模块耦合至性能优越的Triple GEM结构，理论上优化设计快中子探测谱仪参数，研究适用于气体探测器的快中子解谱方法。实验上初步搭建基于多层转化结构的快中子探测谱仪、探究快中子源能谱分布对解谱精度和探测效率的响应曲线，以及开展能量筛选层对快中子成像影响研究。本项目将3D打印技术引入到微模式气体探测器中，有望减小转化层表面不平整造成的探测器内部电场畸变的影响；同时采用基于PXI总线的多路像素读出方式，响应中子束流监测和工业探伤等应用快速诊断的需求。本项目通过采用一套相对简单而且高效的快中子探测方案，达到提高快中子探测效率并获得快中子成像的目的，为下一步研发一种性能可靠的新型快中子成像谱仪打下良好的理论与技术基础。

中子探测器在束流监测、无损探伤、国防和安检等领域应用十分广泛。当前基于微结构气体探测器的快中子成像且具有高探测效率的研究是领域热点。本项目基于气体电子倍增器，在其漂移极耦合了堆栈式聚乙烯薄片作为快中子转化结构，实现了在有限的10cm内使聚乙烯层数提高到了100余层；并利用ANSYS和Garfield数值仿真包对转化层表面静电场、电子在窄小气隙内的输运进行了计算；通过GEANT4对影响快中子探测效率等因素进行了系统研究，量化了转化层的厚度、层数、形状和能量筛选层金属成分的影响；完成了适用于气体探测器的快中子解谱研究；掌握了多层转化结构的设计加工、搭建测试等技术。该成果为中子无损检测提供了一种技术选择，对工业探伤和国防安检都具有重大意义。