提高基于Bulk-Micromegas结构的快中子探测器探测效率和位置分辨的方法的研究

In this proposal, we will concentrate our research work into two aspects: (1) the simulation of three types of polypropylene-based fast neutron (mainly study 14 MeV neutrons) converters and (2) the R&D (Research and Development) of Bulk-Micromegas fast neutron detector based on these converters. .Research work(1):.(A) With Maxwell program, simulates the electric potential and field in the detector, especially in the regions of the fast neutron converters. Here, three polypropylene-based converters with different structures are proposed.Two of them consist of the parallel polypropylene pillars which are perpendicular and 45-degree to the drift cathodes respectively. The third type has the micro-channel sturcture. (B) And then passes the electric field to Garfield program. With this program, the transportation efficiency of electrons in these converters will be simulated. By changing the geometrical parameters of the converters and the electric potentials of the detector's electrodes, the designs of convertors and the configurations of electrodes' potential for best transportation efficiency will be obtained. (C) Furthermore, with Geant4 program, builds the model of detectors with different converters, and simulates their detection efficiency for fast neutrons. By repeating and optimizing the processes of (A), (B), and (C), the designs of converters for best performance of neutron detection will be obtained..Research work(2):.Using the three types of polypropylene converters, designs and develops two types of fast neutron detectors with the sensitive area of 21.6×24.0mm2 and 96.0×96.0mm2 respectively. With the different pressures of the working gas, fast neutron convertors, and electric potential configurations of drift cathodes, the spatial resolution and detection efficiency for 14 MeV neutrons will be studied. With these experiments, the optimized parameters of detectors will be obtained for the best spatial resolution and fast neutron detection efficiency. In addition, the images of different samples, such as lead, polyethylene, boron-loaded polyethylene, and bullets, will be taken by these detectors..In conclusion, two Bulk-Micromegas fast neutron detectors will de developed and studied in details within the scope of this proposal. By optimizing the parameters which can potentially influence to their performances, the fast neutron detectors with the spatial resolution of not-larger-than (better than) 400 microns and the detection efficiency of 1-5%, both parameters for 14 MeV neutrons, will be achieved.

项目主要研究内容:（1）利用Maxwell、Garfield和Geant4程序模拟并优化三种快中子转换膜（与漂移电极垂直的平行聚丙烯柱子阵列、与漂移电极成45度夹角的平行聚丙烯柱子阵列和多孔聚丙烯转换膜）的快中子转换效率和电子传输效率，给出最大转换效率和电子传输效率所对应的转换膜结构参数和探测器的电压配置；（2）设计并制作基于这些转换膜的两种不同灵敏区面积（21.6×24.0mm2和96.0×96.0mm2）和不同读出电极单元形状的Bulk-Micromegas快中子探测器。研究其位置分辨和探测效率随工作气体的不同气压，内部漂移电场以及不同转换膜的结构参数的变化关系，并对不同样品（铅、聚乙烯、掺硼聚乙烯和子弹）进行快中子成像实验。研制出两种不同灵敏区面积和不同读出电极形状的Bulk-Micromegas快中子探测器，其对于14MeV快中子的位置分辨优于400微米，探测效率1-5%。

大面积、高计数率以及耐辐照的中子束流监测探测器在中子应用技术，如成像技术，中有着重要的应用。项目的主要研究内容为：1）利用Maxwell、Garfield和Geant4程序模拟并优化三种快中子转换膜的快中子转换效率，给出最大转换效率和电子传输效率所对应的转换膜结构参数和探测器的电压配置；2）设计并制作基于这些转换膜的两种不同灵敏区面积（21.6×24.0mm2 和96.0×96.0mm2）和不同读出电极单元形状的Bulk-Micromegas 快中子探测器。研究其位置分辨和探测效率随工作气体的不同气压，内部漂移电场以及不同转换膜的结构参数的变化关系，并对不同样品进行快中子成像实验。研制出两种不同灵敏区面积和不同读出电极形状的Bulk-Micromegas 快中子探测器，其对于14MeV 快中子的位置分辨优于400 微米，探测效率1-5%。在具体的研究过程中，研究团队开发出一套基于Maxwell、Garfield和Geant4软件包并能够完整模拟和优化集中不同的快中子转换结构。改软件包可以用于快中子转换结构的设计和优化，从而辅助该类型探测器的设计和性能的优化。除此，还成功地研制出大面积（20X20cm2）二维延迟线读出的Bulk-Micromegas二位快中子成像探测器，模拟和成像实验表明，通过改变转换层的结构和厚度，其探测效率可以在0.1%到5%范围内可调。该探测器的研制成功可以用于快中子成像束流终端的中子束流刨面监测和高强中子束流通量的测量。