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

国际研究奖学金计划使美国科学家和工程师能够在国外进行9到24个月的研究。该计划的奖项提供了联合研究的机会，并利用国外独特或互补的设施、专业知识和实验条件。该奖项将支持尼古拉斯·怀廷博士与英国诺丁汉大学的迈克尔·J·巴洛、彼得·莫里斯和托马斯·米尔斯曼博士以及美国南伊利诺伊大学卡本代尔的博伊德·古德森博士合作，为期24个月的研究奖学金。(HP)稀有气体可用于提高磁共振(MR)检测灵敏度，用于许多潜在和已实现的应用。由于常规磁共振方法获得的核自旋极化通常在~10-5？10-6数量级，这种高压气体表现出的高数量级的自旋极化可以直接转化为相应的MR检测灵敏度的显著增强，从而使许多新的实验和方法成为可能，否则是不可能的。产生高压气体的主要方法之一是自旋交换光学泵浦(SEOP)。SEOP是一个两步过程，角动量从共振的圆偏振激光转移到碱金属蒸气的电子自旋，然后通过碰撞转移到惰性气体的核自旋--允许核自旋极化随着时间积累。SEOP背后的基本物理过程令人惊讶地是多方面的和相互依赖的，尽管对这些过程的光学、原子和分子物理进行了数十年的研究，但它们还没有得到充分的探索；确实，有许多不知道或不了解的东西--特别是当SEOP是在与MR应用最相关的关键制度和实验条件下进行的时候。拟议研究的目标是对涉及特定碱金属和稀有气体的SEOP过程有更深层次的基本了解，并将这些见解应用于需要大量高度自旋极化气体的MR应用中。拟议的研究将涉及使用Rb(Rb)和Cs(Cs)作为碱金属的SeOP，以及作为惰性气体物种的氙气-129(129Xe)和氪-83(83Kr)；虽然Rb/129Xe Seop过去已经得到了很好的表征(尽管不是在本工作建议的条件下)，但涉及Cs/129Xe的研究以及促进四极83Kr/131Xe同位素的极化和MR应用的努力在很大程度上仍处于初级阶段。建议在宿主机构进行的基本SEOP过程的研究包括：碱金属电子自旋极化(PRB/PCS)分布的依赖关系、MAP？利用光学电子自旋共振(ESR)光谱研究了惰性气体的类型和密度、晶胞温度、总压、激光通量、光谱偏移量等；利用拉曼光谱测量氮气的振转温度，研究了OP池内的能量传输机制(作为相同参数的函数)；以及通过低场三维MR成像研究了OP池中相应的核自旋极化分布(和气体动力学)。诺丁汉仪器--PI将帮助完成--将首次允许实时比较所有这些实验观测数据。这些实验不仅将提供有关SEOP的新知识，还将为产生用于磁共振应用的高压气体的条件优化提供信息-包括拟议的实验，将探索使用高度自旋极化的气体来探测多孔材料和表面。虽然拟议的研究本质上是基础性的，但其结果--将在会议演示文稿和出版物中广泛传播--应该对高压气体的新兴和既定应用产生直接影响；这种应用是多种多样的，从材料研究到临床人类肺部空间和组织的磁共振成像。诺丁汉大学作为东道主是独一无二的，因为它在最先进的实验仪器、专家人员和MR创新方面拥有丰富的资源，提供重要的培训和经验，以及建立长期的国际合作，这将在PI的整个专业研究生涯中产生积极的影响。

0966393WhitingThe 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.