DEVELOPING LOW-COST, HIGH-PERFORMANCE METHODS AND INSTRUMENTATION FOR HYPERPOLARIZATION OF 129XE AND 131XE FOR NEXT-GENERATION BIOMEDICAL AND NUCLEAR PHYSICS APPLICATIONS

Author

Abdulbasit Tobi Gafar, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2024

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Goodson, Boyd

Abstract

This dissertation is organized into eight chapters, each focusing on different aspects of Nuclear Magnetic Resonance (NMR) and Spin Exchange Optical Pumping (SEOP), with an emphasis on enhancing nuclear spin polarization and the development of advanced hyperpolarization systems. Chapter 1 introduces NMR, tracing its history and explaining key concepts like nuclear spin, magnetic moment, and fundamental interactions such as the Zeeman effect and chemical shift. The chapter emphasizes NMR's significance in fields like chemistry, physics, biology, and medicine. Chapter 2 explores techniques to enhance nuclear spin polarization, crucial for improving NMR sensitivity. A key concept is hyperpolarization—the creation of high nuclear spin polarization that is well above the weak polarization normally attained at thermal equilibrium conditions. This chapter briefly covers brute-force methods and non-equilibrium approaches like Dynamic Nuclear Polarization (DNP), Parahydrogen-Induced Polarization (PHIP), Signal Amplification by Reversible Exchange (SABRE), and Spin-Exchange Optical Pumping (SEOP), each with distinct advantages, challenges, and applications.Chapter 3 delves into SEOP, given its central role underlying the work in this dissertation. This chapter details SEOP’s historical development, theoretical background, and key mechanisms underlying optical pumping and spin-exchange collisions. It also discusses the practical importance of various experimental aspects, including cell temperature and alkali metal vapor density, as well as emphasizing the role of nuclear spin relaxation in optimizing NMR and MRI applications. Chapters 4 and 5 provide key background information concerning relevant technologies underlying SEOP. First, Chapter 4 examines laser light sources essential for SEOP, focusing on high-power laser diode arrays (LDAs). It also compares various accompanying laser technologies, highlighting Volume Holographic Gratings (VHGs) as an efficient solution for spectrally narrowing LDA output, which is crucial for improving the efficiency of SEOP. Chapter 5 then shifts focus to clinical-scale stopped-flow xenon-129 hyperpolarizers, covering both first- and second-generation developments of this technology. The first-generation design achieved near-unity polarization and demonstrated some automation but encountered challenges in complexity and temperature regulation. The second-generation design improved systems integration, performance, and robustness, making significant strides in clinical applicability. Building from these developments, Chapter 6 details the development of a third-generation stopped-flow xenon hyperpolarizer designed to overcome the limitations of previous designs. Innovations include a compact, mobile structure, an advanced solenoid electromagnet for improved magnetic field homogeneity, and an aluminum heating jacket for precise control over SEOP cell temperature. These enhancements support hyperpolarized 129Xe production for clinical applications such as lung imaging. The chapter also discusses the construction process, operational principles, and SEOP studies conducted to maximize the hyperpolarizer's efficiency and output. Chapter 7 explores the hyperpolarization of a different isotope of xenon—131Xe (a stable quadrupolar isotope)—for neutron-science applications. Following efforts achieving record levels of bulk production of HP 131Xe (albeit still at relatively small scales), this effort moves to scaling up the process in order to investigate the creation of HP 131Xe targets within aluminosilicate (GE180) cells in support of neutron optics experiments investigating time-reversal symmetry violations. As a result of this work, it was possible to create and ship such cell targets for neutron beam experiments in Jülich, Germany. Finally, Chapter 8 presents initial efforts concerning the development of a next-generation modular laser system for SEOP in clinical and fundamental physics applications. Addressing limitations in current laser systems, the new design emphasizes modularity, cost-effectiveness, and improved SEOP efficiency, with preliminary results demonstrating significant advancements and promising enhancements in laser performance, laying the groundwork for future developments.