【作者】 宋仔峰；

【导师】 沈激；

【作者基本信息】 中国科学技术大学 ， 粒子物理与原子核物理， 2010， 硕士

【摘要】 中子具有强穿透性、紧邻元素分辨和非破坏性等特点,可以用来研究物质的微观结构。中子与物质相互作用的截面与其动量成反比,因此,具有较低能量的热中子成为科学研究和新材料研发的重要工具。随着可以提供高通量热中子束的新一代中子源在世界各地相继兴建,大面积的位置灵敏热中子探测器成为一个重要的研究课题。本文主要介绍热中子位置灵敏探测器的一种设计方案。方案基于热中子与硼-10的核反应10B（n,α）7Li,采用10B固体靶物质,探测出射粒子α和产物粒子7Li,采用基于Pads阵列的读出方式,利用重心读出的方法获得中子位置信息。我们采用蒙特卡罗模拟软件Geant4模拟中子与10B反应及α粒子在靶内的分布,给出单层硼靶材的最佳厚度,热中子探测器效率;模拟出射离子的输运过程,给出热中子探测的本征位置分辨能力;模拟出射离子在工作气体里的能量沉积分布及射程,给出探测器的最佳空间结构。根据模拟结果并考虑到使探测器空间结构最小化、工作气体的提供及读出电子学的连接,利用AutoCAD机械设计工具设计出探测器的整体框架和零部件。由气体探测器对工作气体的要求,选择了Ar+CO₂作为探测器的工作气体。由Garfield模拟不同气体混合的倍增结果,给出了气体的混合比例。并建立了一套这样的工作气体的供应系统。根据读出位置分辨的要求及考虑到读出电子学的复杂程度,利用Protel设计了基于Pads阵列读出方式的收集板。利用电磁场模拟软件Maxwell+Garfield模拟了THGEM的最佳空间结构,及实现倍增需要的传输场强和漂移场强的大小,并在此基础上利用Protel设计了供实验测试用的THGEM和给探测器各部件提供电压的分压板。完成了探测器正常工作所需要的供气系统和高压供电系统的建立。对中子转换体硼膜的制备进行了研究,采用粉末冶金法制备了用于PLD实验的硼靶材。根据热中子转换体需要的衬底条件,选择了镀铝的聚酰亚胺薄膜作为衬底。提出了利用PLD法制备硼膜的实验方案,并对制备的硼膜进行了分析。由实验结果可见,制备的硼薄膜表面光滑、无裂痕,可作为热中子转换体,但样品表面硼含量偏低,薄膜厚度还不理想,因此该制备方法还有待进一步提高。实验方面,仅进行了初步的部分实验。完成了探测器高压实验和THGEM漏电流的实验,对利用5.9keV的γ射线测试其能谱的实验还在进行当中。更多还原

【Abstract】 Neutrons can be used to study the material’s microstructure with the features of strong penetrating, distinguishable between close elements, and non-destructive. The reaction cross section of neutron with matter is inversely proportional to its momentum. Therefore, thermal neutrons with lower energy become an important tool for scientific research and new materials’ development. As a series of new generation neutron sources around the world have been built to provide high-flux thermal neutron beams, large-area position-sensitive thermal neutron detectors have become an important research subject.In this paper, a solution of position-sensitive thermal neutron detector is given. The basic principle of designing model is based on the nuclear reaction of thermal neutrons with boron-10: 10B （n,α） 7Li. By using of 10B as the converter material, it is to detect emittedαparticles and the product particles 7Li. The neutrons’position information is given by using of the charge center of gravity readout method and the electronic readout system is based on Pads array.We use Monte Carlo simulation software Geant4 to simulate the process of the neutrons’reaction with 10 B and the result ofα-particle distribution within the target. The best thickness of single boron target and the detection efficiency of thermal neutron detector are given; The transportation process of the emitted ions is simulated and the intrinsic position resolution of thermal neutron detection is given; The range and energy deposition distribution of the emitted ions in the working gas are simulated to give the best spatial structure of the detector.According to the simulation results and taking into account of minimizing the spatial structure of the detector and the supply of working gas and the connections of the readout electronics, the overall framework of the detectors and components are designed by the mechanical design tools of AutoCAD.On the request of working gas for the gas detector, Ar+CO₂ are selected as the working gas of the detector. According to the Garfield simulating the multiplied results of several combinations of the mixed gas, the proportion of the gas mixture is given. And such a working gas supply system is established.According to the requirements of the position resolution and take into account of the complexity of the electronic readout system, the charge collection plate is designed based on the Pads array readout mode by the tool of Protel.The best spatial structure of THGEM is given by the electromagnetic field simulation software of Maxwell and Garfield. The strength of the transmission field and that of drift field which are needed to achieve electron multiplication are also given. And based on the above results, the THGEM for experimental testing and the voltage distribution board which can provide different voltage to the components of the detector are designed by the tool of Protel. The establishment of gas supply system and the high-voltage power supply system is completed.We study the method of preparing the thermal neutron convertor boron film. Powder metallurgy is used to prepare the boron target for the PLD experiments. According to substrate conditions of the thermal neutron converter, the aluminized polyimide film is selected as this substrate. The experimental scheme of preparing boron films by PLD is proposed and the morphology and the composition of these prepared boron films are analyzed. From the results, we can see that the surface of the prepared boron film is smooth, without cracks. It can be used as thermal neutron converter, but the content of boron on the sample surface is relatively low, and the film thickness is not ideal, so the preparation method needs to be improved.Experimentally, only a preliminary part of the experiment is carried out. The high-voltage testing experiment and the leakage current of THGEM measuring experiment are completed; The experiment to measure the energy spectrum of 5.9keVγ-ray is still in progress.更多还原