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

我们对地球及其历史的认识在很大程度上取决于我们对构成地球主体的物质的了解。对地球物质（如岩石、矿物和岩浆）的实验室测量与对地球的直接观测和数值模型相结合，有助于建立我们今天所拥有的关于地球及其内部运作的丰富而复杂的观点。在这个项目中，研究人员试图通过开发一种非常高分辨率的材料表征技术，即正电子湮灭光谱，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完成的。本项目旨在建立一种新的正电子湮灭寿命谱仪，并对该仪器进行测试和校准，对几种重要的地球材料（包括金属、氧化物和硅酸盐矿物）中的原子尺度缺陷族进行表征。这项工作将涉及核物理学家与材料表征和地球科学领域的专家之间的跨学科合作。该项目还将支持两名女教师、本科课程开发和一所文理学院的高级学生研究。了解结晶固体中的缺陷对于我们对地球材料的总体理解是很重要的，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传热特性之间的关系。当晶体结构中包含大量缺陷时，可能会显著影响晶体的输运性质。自然系统中的许多晶体可能暴露于产生缺陷的事件，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，透彻理解缺陷和扩散之间的关系至关重要。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在亚纳米到原子尺度上表征材料缺陷和空隙的非破坏性技术。几十年来，该技术已广泛应用于材料科学和核材料界，用于检测合成材料和工业材料的缺陷特性和辐射损伤的影响，但尚未在地球科学界得到普及。该项目的目标是开发一种方法，通过使用正电子湮灭光谱直接测量各种地球相关材料中的缺陷，从而进一步研究扩散与缺陷种群之间的关系。该项目还将有助于本科生的教育和研究训练，并为矿物物理学、核物理学、材料科学和地球化学之间的跨学科工作提供机会。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识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.