【作者】 郭立平；

【导师】 赵志祥； 成之绪；

【作者基本信息】 中国原子能科学研究院 ， 粒子物理与原子核物理， 2003， 博士

【摘要】 本论文结合当前中国先进研究堆（China Advanced Research Reactor，CARR）中子散射工程谱仪建设的迫切需要，选择国际上广泛使用的通用中子散射谱仪模拟软件MCSTAS和VITESS作为模拟研究工具，首次对若干台新建谱仪的设计方案进行了全面的模拟和优化研究，包括两条冷中子导管、中子应力衍射仪和高分辨中子粉末衍射仪，并配合冷源设计研究了导管对冷源尺寸的要求。本论文的研究结果为中子散射工程建设提供了必要的研究数据，为选择谱仪设计方案提供了基本依据。 在冷源预设计尺寸φ20cm×20cm下，从传输效率和中子流量的角度对特征波长为0.2nm和0.4nm的两条冷中子导管的多种设计方案进行了比较。研究表明，采用m=2的超镜导管较⁵⁸Ni导管或Ni导管可以提高传输效率1.3～2.7倍，并使弯导管的直视长度变短，利于防护屏蔽安排。在满足导管出口中子束的均匀化效果前提下，模拟计算出弯导管后的直导管的最佳长度。在此基础上，分别从传输效率、中子注量率、谱形、发散度、均匀性和重力影响方面，对导管性能进行了技术分析，提出了超镜导管是建设的最佳方案，并被工程设计采纳。 根据导管设计指标的需要，研究了冷源尺寸与堆内导管内壁镀膜材料的全反射临界角和导管系统出口处中子注量率的关系。结果表明，在冷中子导管使用⁵⁸Ni和m=2的超镜镀膜情况下，所需要的冷中子源直径为18cm～22cm，高度为30cm～36cm，并从导管需求的角度为合理的冷源尺寸提出了建议。 用蒙特卡罗模拟方法对中子应力衍射谱仪的设计方案进行了优化研究，提出了一系列可供参考的数据：确定了单色器的位置、尺寸、垂直聚焦单色器在不同起飞角下的聚焦曲率半径和倾角；讨论了第二准直器的尺寸和发散，以及使用第二准直器造成的强度损失；给出了在不同单色器反射面、起飞角、中子波长和第一准直器发散度的情况下样品处的中子注量率，以及多种组合情况下谱仪的分辨率曲线；对限束方孔的尺寸、距离样品远近对强度损失和测量中的影响做了深入研究。用α-Fe多晶样品的（211）晶面进行了模拟实验，得到的衍射峰半高宽以及拉应变和压应中国原子能科学研究院博士学位论文变作用下衍射峰移动的模拟结果都与解析方法的预期值符合得很好。 对高分辨粉末衍射谱仪的设计方案进行了模拟和优化研究，该谱仪主要用于材料的晶体结构和磁结构研究。通过模拟优化研究，对初步设计方案中的单色器和准直器参数作了必要的调整。研究表明，谱仪在高分辨模式和高强度模式下，样品处中子注量率分别达到8.4 x IJ和3 xlo了中子Cm一2·S一’以上，衍射峰最小半高宽分别为O，2450和0.355“，对应的△d/d分别为1.召x 10一又和2.3 xl（）“。对谱仪的主要物理性能进行了全面的分析。更多还原

【Abstract】 According to the demands of neutron scattering instruments to be built at China Advanced Research Reactor (CARR), the designs of several new instruments, i.e. two cold neutron guides (CNG), one neutron stress diffractometer and one high resolution neutron powder diffactometer (HRPD), have been simulated and optimized using Monte-Carlo simulation softwares, MCSTAS and VITESS, first. Requirement on the size of the cold neutron source (CNS) by CNGs has been also studied. The results of this thesis have provided essential data as a basis of the neutron instruments designs.At the pre-design size of the CNS 20cm 20cm, the transmission efficiency and neutron current have been campared among various design scheme of the CNGs with characteristic wavelength of 0.2nm and 0.4nm. It is shown that, by adopting supermirror guides with m=2 instead of 58Ni or natural Ni guides, the transmission efficiency could be increased by the factor of 1.3 ~ 1.7, and the length of direct sight of the curved guides could be shorten greatly, which is useful for arranging shielding. The optimal length of straight guides have been determined by calculating their uniform effect on neutron beam. The performance of the CNGs, including transmission efficiency, neutron flux, flux spectrum, divergency, uniform and gravity effect, have been analysed technically. That the scheme of supermirror guide is optimum has been given and adopted.According to the requirements of the CNG on neutron flux, critical wavelength and distance between inpile guides and the CNS, the relation between the source size and the critical angle of the coating material of the inpile guides as well as neutron flux at exit of the CNGs have been studied. It is shown that, the diameter and height of the CNS,18cm - 22cm and 30cm - 36cm respectively, is necessary, if the 58Ni coating or supermirror coating with m=2 is adopted. The reasonable size of CNS has been suggested.The neutron stress diffiractometer, wich is designed for measuring residual stress or applied stress in materials and engineering components, was simulated and optimized. The position and size of the monochromator, focusing curvature radii and tilting angles of the germanium focusing monochromator under different different take-off angle, size and divergency of the second collimator and intensity loss due to the use of it were determined. The neutron flux at different wavelength, under different reflection and take-off angle of the monochromator and divergency of the first collimator, were given. The simulation on the aperture used for limiting beam size in front of the sample showed that, smaller the size of the aperture and further the distance from the aperture to the sample, greater the loss of the intensity and more serious the spread of the beam along vertical direction at the sample position which makes the practical sampling volume greater than expected. (211) reflection of the polycrystal a-iron sample is used in the simulation experiments, and both the resulting full-width-at-half-maximum(FWHM) of the diffraction peaks and peak shifts under tensive and compressive strain are in accord with that expected from analytical methods. The instrumental resolution curves, under various combination of the first collimator and second collimator and take-off angle of the monochromator, are given.The HRPD, wich is designed for the study of crystal structure and magnetic structure of materials, was simulated and optimized. Some parameters of several components in the initial design, such as collimators and monochromator, were modified after optimization. It is shown that, under the high resolution mode and the high intensitymode, respectively, the neutron flux at the sample position can reach above 8.4 10 and 3 107 neutrons cm-2 -s-1, and the minimum FWHM of the diffaction peaks is 0.245 and0.355 and the correspondent d/d is 1.4 10-3 and 2.3 10-3 , respectively. The main performance of the diffractometer were analysed in detail.更多还原