MRI: Development of an Intense Positron Annihilation Spectrometry System for Nanophase Characterization

MRI：开发用于纳米相表征的强正电子湮没光谱测量系统

• 批准号: 0521270
• 负责人: Ayman Hawari
• 金额: $ 99.96万
• 依托单位: North Carolina State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-09-01 至 2009-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0521270&HistoricalAwards=false
• 关键词: MRI; Development; Intense; Positron; Annihilation

North Carolina State University (NCSU), Oak Ridge National Laboratory (ORNL), and the University of Michigan (UM) have formed a collaboration to develop an intense positron (antimatter electrons) facility at the PULSTAR reactor on the campus of NCSU. Positrons are the antiparticles of electrons and when injected into normal matter they "annihilate" with electrons-that is they both disappear with all of their combined mass being converted into a pulse of electromagnetic radiation according to Einstein's famous formula E=mc2. Positron annihilation is emerging as an ideal probe of advanced materials being developed as part of the nation's Nanotechnology Initiative. Many new applications of nanotechnology involve understanding and manipulating the atomic-scale microstructure of voids within a material. However, fundamental understanding of the role of voids in enhancing or degrading materials properties is often hampered by the inadequacy of traditional techniques (such as electron microscopes) to characterize such voids at the true nanometer scale. Positrons in matter seek out and directly probe such open structures. In the new facility called (NC)3, the North Carolina National Center for Nanophase Characterization, positrons produced near the core of the NCSU nuclear reactor will be piped out to several target stations where students, faculty, and industrial collaborators from around the world can monitor the annihilation process in newly developed materials. By vastly enhancing the access of researchers to an intense, focused beam of antimatter positrons next-generation materials research will benefit from a new way to "see" the structure inside them. The center's research impact is highly leveraged through many applications in science and engineering with broad societal impacts including miniaturized and faster computing, higher strength and longer lasting materials, cleaner energy production, and corrosion- and radiation-resistant coatings.North Carolina State University (NCSU), Oak Ridge National Laboratory (ORNL), and The University of Michigan (UM) have formed a collaboration to develop an intense positron beam facility and associated spectrometers at the PULSTAR reactor on the campus of NCSU. Positrons are emerging as an ideal probe of matter on the nanoscale. The positively charged positron, with its affinity for open structures in matter, has been gaining an important role as a probe of nanostructure and in understanding the role of engineered nanovoids on macroscopic properties. This is mainly due to the increased ability to tailor the macroscopic properties of a material by fine-tuning and engineering its microstructure. The intense positron beam will be created in a converter by pair-production using fission gamma rays produced in the reactor core and by (n,?) reactions in a cadmium cladding surrounding the converter assembly. The positron beam will drive two complementary positron/positronium spectrometers: First, a "next generation" positronium PALS spectrometer (Ps-PALS), with a 1-mm diameter beam, that is capable of performing high accuracy lifetime studies on nanoporus thin films and patterned microelectronic devices, and second, a time-bunched positron PALS spectrometer (e+-PALS) that will be directed for studying annihilation in metals and semiconductors. Ultimately, our goal is to establish (NC)3, the North Carolina National Center for Nanophase Characterization. The core apparatus of (NC)3 is the intense positron beam-line at the PULSTAR reactor, complemented by existing PULSTAR and NCSU systems for neutron scattering, and electron microscopy. The positron beam facility will have applicability in fields such as materials science and engineering, bioscience/biomedical engineering, chemical engineering, electrical engineering, environmental science and engineering, physics and chemistry to name a few. Its main technical focus will be on three aspects of nanophase materials: (a) engineered nanoporosity for improved material properties, (b) the role of nanovoid/defect coalescence in the degradation of materials properties, and (c) interface effects between phases. The development of this facility on a university campus in the United States represents a major research and educational opportunity. The positron facility will also be integrated into the PULSTAR on-line educational network.

北卡罗来纳州州立大学（NCSU）、橡树岭国家实验室（ORNL）和密歇根大学（UM）已经合作，在NCSU校园内的PULSTAR反应堆上开发一个强正电子（反物质电子）设施。 正电子是电子的反粒子，当注入正常物质时，它们与电子“湮灭”-也就是说，它们都消失了，所有的组合质量都被转换成电磁辐射脉冲，根据爱因斯坦的著名公式E= mc 2。 正电子湮没是作为国家纳米技术计划的一部分开发的先进材料的理想探针。 纳米技术的许多新应用涉及理解和操纵材料中空隙的原子尺度微观结构。 然而，从根本上理解空隙在增强或降低材料性能中的作用往往受到传统技术（如电子显微镜）在真正的纳米尺度上表征这种空隙的不足的阻碍。物质中的正电子寻找并直接探测这种开放结构。 在名为（NC）3的新设施中，北卡罗来纳州国家纳米相表征中心，NCSU核反应堆核心附近产生的正电子将被输送到几个目标站，来自世界各地的学生，教师和工业合作者可以监测新开发材料的湮灭过程。 通过极大地提高研究人员获得强烈的、聚焦的反物质正电子束的能力，下一代材料的研究将受益于一种“看到”它们内部结构的新方法。该中心的研究影响通过科学和工程领域的许多应用得到高度利用，这些应用具有广泛的社会影响，包括小型化和更快的计算、更高强度和更持久的材料、更清洁的能源生产以及耐腐蚀和耐辐射的涂层。北卡罗来纳州州立大学（NCSU）、橡树岭国家实验室（ORNL）、和密歇根大学（UM）已经形成了一个合作，在NCSU校园的PULSTAR反应堆开发一个强正电子束设施和相关的光谱仪。 正电子正在成为纳米尺度上物质的理想探针。 带正电荷的正电子由于其对物质中开放结构的亲和力，作为纳米结构的探针以及在理解工程化纳米空隙对宏观性质的作用方面已经获得了重要的作用。 这主要是由于通过微调和设计其微观结构来定制材料的宏观特性的能力增加。 强烈的正电子束将在转换器中产生，通过使用反应堆堆芯中产生的裂变伽马射线和（n，？）在围绕转换器组件的镉包层中发生反应。 正电子束将驱动两个互补的正电子/正电子素光谱仪：第一，“下一代”正电子素帕尔斯光谱仪（Ps-帕尔斯），具有1毫米直径的光束，能够对纳米多孔薄膜和图案化微电子器件进行高精度寿命研究，第二，时间聚束正电子帕尔斯光谱仪（e+-帕尔斯），将直接用于研究金属和半导体中的湮灭。 最终，我们的目标是建立（NC）3，北卡罗来纳州国家中心的纳米相表征。 （NC）3的核心设备是PULSTAR反应堆的强正电子束线，由现有的PULSTAR和NCSU中子散射系统和电子显微镜补充。 正电子束设施将适用于材料科学和工程、生物科学/生物医学工程、化学工程、电气工程、环境科学和工程、物理和化学等领域。 其主要技术重点将放在纳米材料的三个方面：（a）用于改善材料性能的工程纳米孔隙率，（B）纳米空隙/缺陷聚结在材料性能退化中的作用，以及（c）相之间的界面效应。 在美国的一所大学校园里开发这种设施是一个重要的研究和教育机会。 正电子设施也将并入PULSTAR在线教育网络。