Energy measurement and application on material discrimination in muon tomography
Energy measurement and application on material discrimination in muon tomography
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DOI：
10.1109/nssmic.2015.7581957
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发表时间：
2015-10
期刊：
影响因子：
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通讯作者：
Z. Luo;Xuewu Wang;Z. Zeng;Yi Wang;M. Zeng;Jianping Cheng;H. Yi
中科院分区：
文献类型：
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作者：
Z. Luo;Xuewu Wang;Z. Zeng;Yi Wang;M. Zeng;Jianping Cheng;H. Yi
宇宙射线介子层析成像技术是近年来发展起来的一种基于散射理论的方法，由于其对高Z物质的敏感性，可以应用于核物质鉴别。建立了多种不同探测器的介子层析成像系统，如漂移管[2]、Gem[3]、RPC [4]/MRPC[5]、闪烁带[6]和漂移室[7]。由于μ介子能量在物质散射密度重建中的重要性，至少有两种已知尺寸和原子序数的平板上的μ介子谱仪和轨道探测器被用来估计每个出口μ介子[8]的动量，这可能会增加μ介子层析成像系统的复杂性和成本。除了这种介子谱仪之外，还可以采用飞行时间法（TOF）来获取能量。清华大学研制的TUMUTY (Tsinghua University Cube for Cargo Inspection)[5]所采用的MRPC探测器具有良好的空间分辨率和时间分辨率，激发了用TOF法[9]测量μ介子能量的思想。利用6层MRPC探测器获得的μ子轨迹和飞行时间，可以检测到每个μ子的能量。然而，由于μ介子的传播速度几乎与光一样快，用TOF或μ介子光谱仪的方法很难获得高精度的μ介子能量。幸运的是，精确的μ子能量在μ子断层扫描[10]中是不必要的。本文研究了介子能量对材料分辨的影响，初步模拟结果表明，低能介子对散射角分布的影响比高能介子更显著。μ子能量段采用了多层TOF方法，在我们的模拟中，通过该方法获得的低能μ子使得所关注材料之间的均方根差变得更大，从而更容易区分不同的材料。
Cosmic ray muon tomography is a developing method based on scattering theory which can be applied in nuclear material discrimination because of its sensitivity to high Z material in recent years[1]. Various muon tomography systems with different kinds of detectors have been set up, such as drift tube [2], Gem [3], RPC [4]/MRPC [5], scintillator strip [6] and drift chamber [7]. Because of the importance of muon energy in material scattering density reconstruction, muon spectrometer of at least two slabs whose size and atom number are known and track detectors has been constructed to provide an estimate of the momentum of each exit muon [8], which may increase the complexity and costs of muon tomography system. In addition to this kind of muon spectrometer, Time of Flight (TOF) method can also be applied to obtain energy. The MRPC detectors employed in TUMUTY (Tsinghua University Cube for Cargo Inspection) [5], developed by Tsinghua University, have both good spatial resolution and time resolution, motivating the thought of muon energy measurement with TOF method [9]. With the muon track and time of flight obtained from 6-layer MRPC detectors, the energy of each muon can be detected. However, as muon travels almost as fast as light, it is not easy to get the muon energy with high accuracy by TOF or muon spectrometer method. Fortunately, accurate muon energy is not necessary in muon tomography [10]. In this paper, the influence of muon energy on material discrimination has been studied and preliminary simulation results indicate that muons with low-energy have more significant influence on the distribution of scattering angles than high energy. Multilayer TOF method has been employed for muon energy segment and the RMS difference between materials of interest becomes larger with the low-energy muons acquired via this method in our simulation, making it easier to distinguish different materials.