International Research Fellowship Program: Fundamental Studies of Spin-Exchange Optical Pumping for the Production of Large Quantities of Highly Spin-Polarized Noble Gases

Whiting Nicholas R, Carbondale IL

Investigators

Abstract

0966393 Whiting The International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad. This award will support a twenty-four-month research fellowship by Dr. Nicholas Whiting to work with Drs. Michael J. Barlow, Peter Morris, and Thomas Meersmann at the University of Nottingham in the United Kingdom and with Dr. Boyd Goodson at Southern Illinois University Carbondale in the United States. ?Hyperpolarized? (HP) noble gases can be used to enhance the magnetic resonance (MR) detection sensitivity for a host of potential and realized applications. Because the nuclear spin polarization achieved in conventional MR methods is usually on the order of ~10-5?10-6, the orders-of-magnitude higher spin polarization manifested by such HP gases can translate directly into correspondingly massive enhancements in MR detection sensitivity?thus enabling a wide range of novel experiments and approaches that would not be possible otherwise. One of the primary methods for generating HP gases is spin-exchange optical pumping (SEOP). SEOP is a two-step process where angular momentum is transferred from resonant, circularly polarized laser light to the electronic spins of an alkali metal vapor, and then subsequently transferred to the nuclear spins of a noble gas via collisions?allowing the nuclear spin polarization to accumulate over time. The fundamental physical processes underlying SEOP are surprisingly multifaceted and interdependent, and despite decades of research into the optical, atomic, and molecular physics of these processes, they have yet to be sufficiently explored; indeed, there is much that is not known or understood?particularly when SEOP is performed under key regimes and experimental conditions that are most relevant for MR applications. The objectives of the proposed research are to gain a deeper fundamental understanding of SEOP processes involving selected alkali metals and noble gases, and to apply these insights to improve SEOP for MR applications requiring large amounts of highly spin-polarized gases. The proposed research will involve SEOP using both rubidium (Rb) and cesium (Cs) as alkali metals, and xenon-129 (129Xe) and krypton-83 (83Kr) as noble gas species (with the possibility to expand to 131Xe); while Rb/129Xe SEOP has been well characterized in the past (although not under the conditions proposed in this work), studies involving Cs/129Xe as well as efforts to boost the polarization and MR applications of the quadrupolar 83Kr/131Xe isotopes are still largely in their infancy. The proposed studies of fundamental SEOP processes at the Host institution include: the dependence of the alkali metal electronic spin polarization (PRb/PCs) distribution ?map? on noble gas type and density, cell temperature, total pressure, laser flux, spectral offset, etc. using optical electron spin resonance (ESR) spectroscopy; investigations of energy-transport mechanisms within the OP cell (as a function of the same parameters) using Raman spectroscopy to measure the rovibrational temperature of nitrogen gas; and studies of the corresponding nuclear spin polarization distribution (and gas dynamics) across the OP cell via low-field 3-D MR imaging. The Nottingham apparatus?which the PI will help complete?will for the first time allow the comparison of all of these experimental observables in real time. These experiments will not only provide new knowledge concerning SEOP, but will inform the optimization of conditions for generating HP gases for MR applications?including proposed experiments that will explore the use of highly spin-polarized gases for probing porous materials and surfaces. While the proposed research is fundamental in nature, the results?to be widely disseminated in conference presentations and publications?should have a direct impact on both emerging and established applications of HP gases; such applications are manifold and vary from studies of materials to clinical human MR imaging of lung spaces and tissues. The University of Nottingham is uniquely positioned to serve as host, given its vast resources in state-of-the-art experimental instrumentation, expert personnel, and strong history in MR innovation?providing vital training and experiences, as well as establishing long-lasting international collaborations, that will positively impact the PI throughout the duration of his professional research career.