EAGER: Collaborative Research: Positron annihilation spectroscopy of Earth materials: A combined materials characterization approach

我们对地球及其历史的了解在很大程度上取决于我们对构成地球大部分的物质的理解。地球物质的实验室测量（例如，岩石、矿物和岩浆）与对地球的直接观测和数值模型一起使用，以帮助建立我们今天所拥有的丰富而复杂的地球及其内部运作的视图。在这个项目中，研究人员试图通过开发一种称为正电子湮没光谱的非常高分辨率的材料表征技术，进一步了解几种相关地球材料的原子尺度物理特性。这项技术的好处是，它允许在原子水平上直接研究结晶固体，这是地球科学中使用的其他常规方法所不能做到的。该项目旨在建立一个新的正电子湮没寿命谱仪，测试和校准仪器，并表征几种重要的地球材料，包括金属，氧化物和硅酸盐矿物中的原子尺度缺陷种群。这项工作将涉及核物理学家与材料表征和地球科学领域专家之间的跨学科合作。该项目还将支持两名女教师，本科课程的开发，并在文科学院先进的学生研究。了解晶体固体中的缺陷对于我们对地球材料的一般理解很重要，因为它们与晶体内的原子迁移率（扩散），晶体的成核和新相的形成以及电和热传递特性有关。当晶体结构中包含大量缺陷时，其可显著影响晶体的输运性质。自然系统中的许多晶体可能已经暴露于缺陷产生事件，包括辐射损伤和变形。为了准确地将实验确定的扩散参数应用于自然系统，对缺陷和扩散之间的关系的透彻理解是至关重要的。通常缺乏对天然和合成地球材料中缺陷数量的直接测量。正电子湮没光谱是一种非破坏性的技术，用于在亚纳米到原子尺度上表征材料中的缺陷和空隙。几十年来，该技术已在材料科学和核材料界广泛使用，以检查缺陷特性和辐射损伤对合成和工业材料的影响，但尚未在地球科学界普及。该项目的目标是开发一种方法，通过使用正电子湮没光谱法直接测量各种地球相关材料中的缺陷，进一步研究扩散和缺陷数量之间的关系。该项目还将为本科生的教育和研究培训做出贡献，并为矿物物理、核物理、材料科学和地球化学之间的跨学科工作提供机会。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Our knowledge of the Earth and its history strongly depends on our understanding of the materials that make up the bulk of the planet. Laboratory measurements of Earth materials (e.g., rocks, minerals, and magmas) are used in conjuction with direct observations of the planet and numerical models to help build the rich and complex view of the Earth and its inner workings that we have today. In this project, the investigators seek to further our understanding of the atomic-scale physical properties of several relevant Earth materials through the development of a very high resolution materials characterization technique called positron annihilation spectroscopy. The benefit of this technique is that it allows for direct investigation of crystalline solids at an atomic level, which is not routinely done with other conventional methods used in the geosciences. This project aims to build a new positron annihilation lifetime spectroscopy apparatus, test and calibrate the instrument, and characterize the atomic scale defect populations in several important Earth materials including metals, oxides, and silicate minerals. The undertaking will involve interdisciplinary collaborations between nuclear physicists and experts in the area of materials characterization and geoscience. The project will also support two female faculty, undergraduate curriculum development, and advanced student research at a liberal arts college. Understanding defects in crystalline solids is important for our general understanding of Earth materials because of their relationship to atomic mobility (diffusion) within crystals, nucleation of crystals and formation of new phases as well as electrical and heat transfer properties. When a significant population of defects are included in the crystal structure, it may affect transport properties of the crystal significantly. Many crystals in natural systems may have been exposed to defect creating events including radiation damage and deformation. To accurately apply experimentally determined diffusion parameters to natural systems, a thorough understanding of the relationship between defects and diffusion is crucial. Direct measurements of defect populations in natural and synthetic Earth materials is generally lacking. Positron annihilation spectroscopy is a non-destructive technique used to characterize defects and voids in materials at a sub nm to atomic scale. The technique has been used extensively in the materials science and nuclear materials communities for decades to examine defect properties and the effects of radiation damage on synthetic and industrial materials, but has not yet gained popularity in the Earth sciences community. The goal of this project is to develop a methodology that will enable further investigation into the relationship between diffusion and defect populations by direct measurement of defects in a variety of Earth relevant materials using positron annihilation spectroscopy. The project will also contribute to the education and research training of undergraduate students and provide opportunities for interdisciplinary work between mineral physics, nuclear physics, materials science, and geochemistry.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.