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

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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.