【作者】 叶瑾；

【导师】 程建平；

【作者基本信息】 清华大学 ， 核科学与技术， 2009， 博士

【摘要】 利用宇宙线对重核物质进行成像的技术是一种新型重核物质检测技术。本课题利用宇宙线μ子作为粒子射线源,采用新型高位置分辨阻性板室(Resistive Plate Chamber,简称RPC)气体探测器系统,研制成功了可实现宇宙线重核成像的系统,获得了具有较好分辨率的20cm×10cm×15cm铅块的宇宙线辐射成像实验结果。首先开展了利用宇宙线μ子对高Z物质成像的可行性研究。利用蒙特卡罗模拟工具Geant4模拟了μ子与不同原子序数物质的相互作用,分析μ子经过多次库仑散射后的散射角分布与物质原子序数的关系。通过对散射角分布的分析,提出了μ子径迹探测器亚毫米级的位置分辨要求,以及系统原型设计方案。PoCA算法(Point of Closest Approach algorithm)是一种利用μ子多次库仑散射角分布与物质原子序数的对应关系而建立的宇宙线辐射成像算法。本论文软件实现了PoCA成像算法,利用该算法对蒙特卡罗模拟实验数据进行图像重建,并研究了散射角测量误差对重建图像的分辨率的影响。阻性板室探测器探测效率能达到95%以上,可大面积使用、成本低、制造工艺相对简单,可作为μ子径迹探测器。理论研究了感应电荷在阻性膜上的扩散过程。从理论和实验两方面分别分析了信号采集时间窗口以及阻性膜的面电阻率大小对电荷扩散的影响。研制了具有亚毫米级位置分辨能力的一维信号读出RPC、二维信号读出RPC、大面积二维信号读出的高位置分辨RPC探测器。探测器的位置分辨能力、探测效率等重要指标达到国际同类探测器的领先水平。搭建了灵敏探测体积为40cm×40cm×80cm的宇宙线辐射成像系统,具有80%的探测效率。对系统中各探测器的空间定位方法进行了实验研究并确定了系统位置修正方法。对20cm×10cm×15cm的铅块进行了宇宙线辐射测量并重建图像,获得了分辨率较好的宇宙线辐射成像实验结果。本课题对宇宙线辐射成像技术中的高位置分辨探测器、成像算法等几项关键技术进行了深入研究,得到了高水平的研究结果。建立了利用宇宙线对重核物质的空间分布进行检测的原理性系统,取得了较好的宇宙线对重核材料的成像结果。更多还原

【Abstract】 Radiography of high Z material with cosmic ray muon is a novel technology for heavy nuclear material detection. Using cosmic ray muon as particle source and a novel resistive plate chamber with high position resolution as muon tracking detector, a system is successfully developed to realize high Z material radiography with cosmic ray. The system achieved good experimental result on radiography of 20cm×10cm×15cm lead cube with cosmic ray.The possibility of radiography of high Z material with cosmic ray has been firstly discussed. Basing on the Monte-Carlo calculations for muon interaction with matters, the Multiple Coulomb scattering (MCS) is studied. MCS represents an information source that is almost as sensitive to material Z as energy loss. Materials with different Z can be discriminated by MCS angle distribution with cosmic ray muon. The research on scattering angle distribution shows that less than a millimeter position resolution and high efficiency is required for muon detector due to low muon rate on sea level.In this article, it has been introduced the principle of imaging of heavy nuclear material distribution with cosmic-ray muon. The method has been described in details for the judgment of existence of heavy nuclear materials in scanned space and the imaging algorithm of its distribution. This imaging method has some advantages for heavy nuclear material monitor when comparing with traditional X-ray imaging method. Our own endeavor for application of this new imaging method has also been given.Point of Closet Approach algorithm ( PoCA ) is formalism of cosmic ray muon radiography using MCS as information source. It is an extending of traditional tomographic methods for different z materials discrimination. A process based on PoCA algorithm is developed and tested with simulation data derived from Monte-Carlo calculation. Some random signal simulated real data error is added to simulation data for the research on resolution of imaging reconstruction result.RPC has been used widely for high energy charged particle detection, especially for muon detection in large scale spectrometer in the domain of high energy physics due to its superior time resolution, high efficiency above 95%, moderate position resolution, simple manufacture and more important low cost. The charge dispersion of induced signal on resistive plane affects position resolution. The influence of surface resistivity of high voltage provider which is usually carbon film and the selection of integrated FADC time window on the dispersion of induced charge is studied by theoretical calculation and experimental results. A new kind of resistive plate chamber with less than 1mm statistical position resolution is developed and then extended to large area with 2D readout structure. The position resolution and efficiency factors have been level ahead of the world in the same field.Finally, the system of radiography with cosmic ray muon is established. It has a 40cm×40cm×80cm effective detecting field and the efficiency is up to 80% . A research on muon tacking reconstruction and calibration for groups of detector displacements is carried out. The result of radiography of 20cm×10cm×15cm lead cube has high qualities in reconstructed image.This dissertation is to set up a radiography system with cosmic ray and get good reconstruction results of high Z material. Meanwhile, the main technology on high position resolution detector and radiography algorithm is developed.更多还原