新型快中子望远镜关键技术研究

Fission neutron detectors have been regarded as important equipment for special nuclear material (SNM) inspection. The key issue for effectively identifying of SNM has been regarded as detector sensitivity to fission neutrons in field scenario. We propose a novel fast neutron telescope prototype detector with capabilities of fast neutron imaging and energy measurement for 1-10MeV neutrons. The imaging concept bases on neutron-proton elastic scattering resulting in rejection of the majority of background neutron events. Therefore, the sensitive area of detector to background neutrons can be reduced significantly. Moreover, the microstructure detector concept integrates micro scintillator bars with micro silicon photomultipliers (SiPMs) so as to improve the fill factor of neutron sensitive materials in the detective volume. As a result, detection efficiency for fission neutrons can be increased. This design aims for solving the contradiction between reduction of sensitive area to background neutrons and increase efficiency for fission neutrons. In addition, increase of the overall detector sensitivity has been expected. Investigation will be made for improvements of neutron energy resolution, neutron scattering angle resolution, neutron detection efficiency and neutron/gamma identification.

用于裂变中子探测的中子探测器是特殊核材料监测的重要设备。提高中子探测器的灵敏度是实现特殊核材料快速、高效识别的关键因素。本项目提出的快中子望远镜是兼具中子能量测量及中子源成像能力的新型中子探测器，探测能区1-10MeV。探测器设计方案采用快中子-质子弹性散射成像方法，有效排除掉大部分环境本底中子事例，降低了探测器对背景中子的灵敏面积；采用微结构探测器设计思想，将微型闪烁体探测单元与微型硅光电倍增管相结合，显著提高了中子灵敏材料在探测器有效探测空间内的填充比例，提高了中子探测效率。设计方案解决了国际同类型探测器方案中降低背景中子灵敏面积与提高信号中子探测效率不能同时兼顾的缺点，有利于提高中子探测器的灵敏度。拟解决的关键技术问题包括：中子能量分辨、中子散射角分辨、中子探测效率及中子/伽玛粒子鉴别效率的优化方法。

快中子成像探测装置按照成像原理可分为编码成像（时间编码、孔径编码）及中子散射成像两类。本项目研究的新型快中子望远镜是基于中子散射成像原理的快中子成像探测器，具有全向视场中子成像和中子能谱测量的功能，可应用于特殊核材料检查、中子源成像等领域。此类探测器研究重点在于提高成像角分辨和中子探测效率。本项目设计制作了探测器单元模型，对探测单元基础性能指标之一核反冲质子位置分辨指标开展了优化研究，模型实验结果表明：对于1.63-2.60MeV核反冲质子探测单元位置分辨达到5.48mm，对于4.82-5.50MeV核反冲质子位置分辨达到4.60mm，相比以前文献报道的厘米量级位置分辨有所提高。探测器单元对核反冲质子的探测阈能为1.18MeV。探测器单元位置分辨指标的提高将有助于改善探测器中子成像角分辨，进而提高中子探测灵敏度。