利用半影锥成像诊断中子源区图像的新技术研究

Neutron imaging is a key diagnostic technique in the nuclear physics and usually used to diagnose the neutron source and measure the core of nuclear reaction. The traditional aperture for neutron penumbral imaging is hollow, the fabrication precision is difficult to be satisfied; X-ray CT imaging cannot be used to detect because of the thickness. In order to reduce the difficulties of fabrication and detecting, the aperture is newly designed by Monte Carlo method. The diagnostic power of neutron penumbral cone imaging is the same as the neutron penumbral aperture imaging, but the penumbral cone can be easyly fabricated and detected. The structure of the penumbral cone is simple and can be machined by the electric spark incision technology. The shape of the penumbral cone is thin and can be detected by the X-ray CT imaging. The technique will be researched by the theory and experiment, Including designing the penumbral cone imaging system, analyzing the spatial resolution, estimating the aperture-fabrication error and misalignment, investigating the method of reconstruction in the theory; also finishing the machining and detecting of penumbral cone, and the demonstrating experiment. The project will provide a new idea of diagnosing the neutron source by penumbral cone imaging, which is the best technique way to solve the difficulty of the fabrication. This technique provides a high precision diagnostic method for neutron source, and will be availability in nuclear experiment, the implosion experiment of inertial confinement fusion and magnetic confinement fusion.

中子成像是核物理领域的关键诊断技术，常用于中子源检测、核反应芯区测量。传统的中子半影成像所用的双锥型半影孔中空，加工无法达到5μm的精度；半影孔壁厚，X射线CT成像无法穿透。本项目针对半影孔加工和检测困难的缺点，使用蒙特卡罗程序设计了诊断能力与之一样，但加工和检测相对简单的半影锥成像系统。半影锥结构简单，电火花切割技术已能加工；形状细长，X射线CT成像可以检测。本项目包括理论设计半影锥成像系统、分析系统空间分辨率、分析系统加工和瞄准要求、研究图像重建方法；完成半影锥的加工和检测，以及半影锥成像的演示性实验。本项目提出的利用半影锥成像诊断中子源区图像的概念未见公开报道，也是目前解决国内编码装置加工难题的最佳技术途径。提供的中子源区高精度诊断方法，对中子诊断技术的发展，对中子辐射源的检测，对核实验、天体物理实验室模拟、惯性约束聚变和磁约束聚变研究中的内爆物理实验诊断等研究具有重要意义。

针对半影孔加工和检测困难的缺点，本项目使用蒙特卡罗程序设计了半影锥成像系统。根据神光Ⅲ主机装置中子产额条件，确定成像系统排布参数；根据点扩展函数的尖锐性和等晕性要求，确定半影锥参数；模拟半影锥系统的分辨率，以及在不同加工精度、偏心误差、旋转误差和物距误差时，对成像质量的影响。模拟结果表明，系统分辨率能达到15μm，半影锥椭圆度的加工误差要小于0.1，瞄准的偏心误差要小于60μm，旋转误差要控制在0.35mrad以内，物距误差要控制在1mm以内。然后，根据设计结果，使用高精度磨床完成半影锥加工。检测结果表明，精度满足5μm要求，圆形度较好。最后，基于X光微点源，从实验角度验证了半影成像的原理。利用针孔成像，直接测量了微点源源区图像；给出半影孔成像、半影锥成像和环孔成像原理，以及在微点源的半影成像结果和维纳滤波重建结果。从结果可知，半影锥成像具有与半影孔成像一样的诊断能力，而环孔成像的诊断能力更好。对重建算法的比较显示：维纳滤波对噪声的容忍性较好，适当除噪能适当的提高重建效果；RL算法对噪声的容忍性不如维纳滤波好，除噪不能提高重建效果；CT重建不适用高噪声半影像。