【作者】 赵力；

【导师】 张子平； 王贻芳；

【作者基本信息】 中国科学技术大学 ， 粒子物理与原子核物理， 2006， 博士

【摘要】 本论文首先简要地介绍了粒子物理和粒子探测器的历史和现状。随着现代计算机技术和电子学的发展，高能物理对粒子探测器的性能要求越来越高，能否发现新的粒子和物理现象取决于大型探测器的整体性能。北京正负电子对撞机(Beijing Electron Positron Collider，BEPC)由直线加速器、束流运输线、储存环和北京谱仪(Beijing Spectrometer，简称BES)组成，是我国进行高能物理实验的一个很重要的大型仪器，凭借它使我国在国际高能物理研究中占有一席之地。虽然过去曾取得一些重大成果，但现在该探测器已经老化了，并且随着国际高能物理的快速发展，它已很难继续保持在τ-粲能区物理研究的领先地位。因而，现在正需要在过去成功运行的基础上对BEPC／BESⅡ进行升级改造，大幅度提高其性能，从而继续取得国际高水平的物理成果。然而，大型探测器整体性能的好坏取决于每个子探测器的好坏，只有将每个子探测器设计好并精确地安装，升级改造工程才可能圆满完成。 本论文的核心主要是对塑料闪烁体型飞行时间计数器(Time of Flight，TOF)的研究。该探测器是正在建造中的BESⅢ一子探测器，它鉴别动量小于1 GeV／c的带电粒子K／π的能力是很强的，同时它也提供快触发和事例定时信息。由于其技术较成熟，这种探测器应用相当广泛。然而，为了使BESⅢ的TOF探测器的性能达到或超过国际先进水平，必须对该探测器进行详细的研究和测试。 作为TOF计数器的两个重要组成部分—闪烁体和倍增管，它们的性能是相当关键的。经过仔细调研并参考其他探测器，挑出了三种快闪烁体：BC-408，BC-404和EJ-200。实验研究显示它们发射谱的峰位分别是425nm，407nm和426nm，且发射谱的形状和峰位在闪烁体被辐射源大剂量辐照后依然不变；它们的相对光产额会随辐照剂量的增加而减小；在弱辐照后，100小时内没有观察到明显的光产额恢复效应；BC-408和EJ-200在发射峰处的透过率为70％左右，BC-404的略低。因而对于估计的在BEPCⅡ上每年将受到的10Gy剂量来说，这些闪烁体都没有问题，但优先考虑闪烁体BC-408和EJ-200。考虑到闪烁体的尺寸和发射谱，谱仪的有限内部空间以及倍增管的性能参数，选择了Hamamatsu公司生产的较短倍增管R5924，测试表明其抗磁性和时间性能满足要求。 我们对由塑料闪烁体和倍增管组成的单根TOF计数器进行了束流试验和模拟，束流试验的读出电子学是由NIM(Nuclear Instrument Module)／CAMAC插件和机箱组成的。长条形闪烁体的测试实验是利用了高能所提供的干净次级粒子束流，然而为了获得其准确的时间分辨率，参考时间起点的时间晃动必须尽可能地小。为此，设计了几种薄快闪烁体+快倍增管的组合方案，其中最小的时间晃动可达44±2ps。铝膜包装的，长2.3m宽6cm而不同厚度的塑料闪烁体BC-408的实验结果表明5cm厚的闪烁体搭配倍增管R5924表现出最佳性能，而不是6cm厚的闪烁体，模拟结果显示其主要原因是倍增管的有效接受面积限制了收集到的光电子数目。而由不同的反射材料包装的EJ-200的实验结果显示反射材料的反射率增大其时间性能不会一直变好，模拟显示被反射回来的大量光子会破坏脉冲前沿，从而抑制了时间性能的提高。 最后，由闪烁体、倍增管、快前放、18m差分电缆，以及由VME机箱和9U模块板构成的读出电子学组成了完整的TOF系统，并进行了束流试验，结果表明在闪烁体中间位置的包括电子学晃动在内的时间分辨率为：70±2ps(质子)，更多还原

【Abstract】 This paper begins with a brief introduction of the past and current status of particle physics and particle detector. The performance of the particle detector becomes more and more important for high energy physics as the modern technology of computer and electronics grows; the discovery potential of new particles and physical phenomena is determined by the whole performance of the huge detector. The Beijing Electron Positron Collider (BEPC), composed of the linear accelerator, the transportation line, the storage ring and the Beijing Spectrometer (BES), is a most important machine for high energy experiment in our country, and makes us have a seat in the international community of high energy physics research. Although it had great achievements in the past years, but now as the detector became aged it is hard for it to continuously play a leading role in the tau-charm physics study to meet the requirement of rapid development in high energy physics. Hence, it is the right time to upgrade BEPC machine and BESII detector, to make its performance be greatly improved based on its past successful operation, and then the high-class physics results in the world would be obtained continually. However, the whole performance of the huge machine depends on its each sub-detectors; the upgrade project would be completed successfully only if all its sub-detectors are better designed and precisely installed.This dissertation is mainly focused on the study of Time-of-Flight (TOF) counter system made of plastic scintillator. As a sub-detector of BESIII currently under construction, TOF system is powerful for charged particle identification (PID) of K/π with a momentum less than 1 GeV/c. At the same time it can also provide the fast trigger and event timing information. This kind of detectors is widely used because of its mature technology. However, in order to make the performance of BESIII TOF counter close to or exceed the international advanced level, some detailed studies and beam tests have to be done.The properties of the scintillator and photomultiplier, the two important part of TOF counter, are very pivotal. Through detailed investigation and referring to other detectors, three kinds of scintillators, BC-408, BC-404 and EJ-200, are selected. The peak position of their emission spectrum is at 425 nm, 407 nm and 426 nm respectively from experimental study, this peak position and shape of the spectrum remains unchanged even after being irradiated by strong irradiation resource; the relative light yield of all the samples decreases when the radiation dose increases; no evidence of recovery of light yield is observed within 100 hours after weak irradiation; the transmittance of BC-408 and EJ-200 is about 70%, and that of BC-404 is just little lower. Hence, all of them can be used for the TOF counter since the estimated dose rate at BEPCII is 10 Gy per year, but BC-408 and EJ-200 are preferred. Considering the size and emission spectrum of scintillator, the limited detector inner space, and the parameter of PMT, the shorter PMT R5924 made by Hamamatsu Company is chosed. The test results show that the diamagnetism and time performance of PMT R5924 meets our goals.The beam test and Monte Carlo simulation of a single TOF counter composed of更多还原