【作者】 周日峰；

【导师】 陈伟民；

【作者基本信息】 重庆大学 ， 光学工程， 2011， 博士

【摘要】 工业计算机层析成像技术(Industrial Computed Tomography,简称工业CT)能直观、清晰、准确地检测被测物体断面内部的结构组成、密度变化以及缺陷的性质、位置及大小,被人们喻为最佳、最具发展前景的无损检测技术之一。高能工业CT采用电子直线加速器为X射线源,具有穿透力更强、检测精度更高、扫描速度更快等特点,满足了航空航天、国防军工以及交通运输(如高速铁路等)、钢铁冶金、地质、石油等行业的大型构件和大型装备的特殊的无损检测需求,是保障这些特殊产品的质量与安全必不可少的重要手段,因而具有巨大的社会价值和应用价值。探测器是高能工业CT系统的关键部件,对保证高能工业CT的检测效率、空间分辨率与密度分辨率等关键性能至关重要。然而,由于目前常用的闪烁体探测器存在抗辐射能力差、探测器窜扰大、环境条件要求高、制备复杂价格昂贵、电子学噪声大动态范围受限制等缺点,在很大程度上还不能完全满足高能工业CT的使用要求。气体电离室探测器具有抗辐射能力强、性能稳定可靠、成本低廉、暗电流小动态范围大等优点,但也存在探测效率低和体积大这两大致命缺陷,严重影响高能工业CT的检测效率及分辨率等关键指标。到目前为此,探测器仍是制约高能工业CT技术进一步发展的主要技术瓶颈之一,也是限制这一先进无损检测技术普及和推广的重要原因之一。由于闪烁体探测器受工作原理及材料性能等限制,其性能很难有大幅度的提高。气体电离室探测器除了探测效率低和体积大两大缺点外,具有许多闪烁探测器难已比拟的优点,有很大的发展空间和潜能。为攻克气体电离室探测效率低、体积大这两大难题,由国家自然科学基金项目和重庆市科技攻关项目资助,深入研究和探讨了高能X射线辐射探测理论、气体电子倍增(GEM)机理等相关理论,提出了高能工业CT新型气固混合型电子倍增辐射探测器方案,并搭建了实验测试平台,为新型气体电离室探测器的实际应用奠定了理论和实验基础。主要工作如下:(1)通过分析高能X射线工业CT目前发展遇到的问题和技术瓶颈,结合我国高能工业CT目前的发展状况,全面地比较、分析和总结了高能工业CT目前常用探测器的优点和不足,提出本论文总体研究思路和研究工作要点。(2)通过对电子直线加速器高能脉冲X射线辐射探测理论和气体电子倍增(GEM)机理等相关理论的深入研究和探讨,结合高能工业CT的特殊结构,创新性地提出了新型气固混合型电子倍增辐射探测器方案。通过创新性地采用薄高密度金属片作为光电转换体来提高气体电离室探测器效率,用GEM(电子倍增器)来减小气室体积的全新的气固混和型探测器结构方式,解决了传统气体电离室探测器探测效率低、体积大这两大难题,为高能X射线工业CT提供性能优良、价格低廉的探测器开拓了新的途径。(3)建立基于GEM电子倍增原理的高能工业CT气固混合型电子倍增辐射探测器物理模型,用理论分析和计算机仿真相结合的方法,对探测器方案的可行性进行了理论分析和论证。(4)根据理论计算和仿真结果,试制了探测器样品,并设计了相关的观察和测试实验。在现有高能工业CT实验研究平台的基础上,搭建了探测器实验平台,并完成了相关的实验测试。实验中用示波器直观地观测到了探测器单元输出模拟信号的波形、幅值大小,测量了探测器输出信号强度与输入的X射线强度变化,表明探测器不仅具备把X射线粒子转换为电信号的基本功能,而且其输出信号强度与X射线强度存在良好的线性关系,证明了探测器方案的可行性。通过实验,也发现了探测器存在诸多问题和不足,为进一步提高探测器性能和最终实现产品化、实用化奠定了基础。最后,总结了全文研究工作和创新之处,指出了论文的不足和近期有待进一步研究的问题。更多还原

【Abstract】 Industrial Computed Tomography(ICT), compared to conventional radiogram technology, produces accurate images of the internal features of objects, as well as information about the defect’s property and position . ICT technology is considered one of the best nondestructive testing methods. The high energy X-ray Industrial Computed Tomography (HECT) system with an electron linear accelerator is developed to image cross-sections of large scale and high density materials. Owing to strong radiation penetrability as well as high spatial resolution and fast scanning speed, HECT is broadly applicable to various fields as an important tool for nondestructive testing (NDT) and nondestructive evaluation(NDE), such as automobile engine, high speed railroad casting and solid fuel rocket motors and so on .The detection system is the key parts of HECT because the high spatial resolution, rapid inspects efficiency, flexible scan mode and low price of HECT are determined by the detection system. However, nowadays, the level of the detection technology is not satisfied the requests of the development of HECT. The scintillator detectors which are most commonly used have many shortcomings such as poor radiation resistance, great cross-talk, high environment condition, costliness, narrow dynamic range and so on. The gaseous detectors have many merits such as low cross-talk and wide dynamic range, but some serious defects are their low detection efficiency and big volume. In certain extent, the shortcoming of the detector is the most reason which restricts the development of HECT technology and holds back the broadly applicable to some fields. Currently, the study of the detection technology of HECT became an important part of HECT research work.Due to the restriction of the detection principle and the material performance the improvement of scintillator detectors is very hard. However, the gaseous detectors have great development space if we can conquer the two shortcomings, the low detection efficiency and the big volume. In this dissertation, supported by National Natural Science Foundation of China and by Tackling Key Problems of Science and Technology of ChongQing, the principle of the high energy X-ray detection and the mechanism of gaseous detector and gas electron multiplier (GEM) are studied, and a new type of solid-conversion gaseous detector was investigated. Some valuable results have been obtained. The main work is provided as follows: ①By analyzing the problems which have been meet in the development of the HECT, and by analyzing the disadvantages of the HECT detectors which have been widely used currently, we put forward key points in this dissertation.②A new type solid-conversion gaseous detector for HECT has been proposed based on the profound analysis of the theory about the pulse X-ray and the GEM. In this detector, a tungsten slab is employed as a radiation conversion medium, and makes the GEM as electron amplifier to resolve the contravention of the size and the detection efficiency of the gas detector.③The feasibility of the solid-conversion gaseous detector is analyzed and demonstrated by the model based on the GEM with theory analysis methods and computer simulation methods.④The sample of the solid-conversion gaseous detector has been designed and produced according to the results of computer simulation and the theoretical calculation . In addition, we set up a trial platform and contrive some experimental schemes. In the experiment, the analog signals waves of the detector unit were shown in distinctly, and the experiments proved that the output of the detector is proportion to the intensity of the incident X-ray. The results of the experiments show that the schemes of gas-solid electron multiplier detector of high energy x-ray industrial CT are reasonable.At last, this thesis reviews the whole research work, summing up innovations as well as shortcomings in it, some important issues are expected to be perfected and lucubrated in the near future.更多还原