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

[09663993]怀特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至24个月的研究。该计划的奖励为联合研究提供了机会，并利用独特或互补的设施、专业知识和国外的实验条件。该奖项将支持尼古拉斯·怀廷博士与尼古拉斯·怀廷博士一起进行为期24个月的研究。英国诺丁汉大学的Michael J. Barlow， Peter Morris和Thomas Meersmann，以及美国卡本代尔南伊利诺伊大学的Boyd Goodson博士。（HP）惰性气体可用于提高磁共振（MR）检测灵敏度，具有许多潜在和已实现的应用。因为在传统的磁共振方法中获得的核自旋极化通常在~10-5？10-6，这种高压气体所表现出的更高的自旋极化数量级可以直接转化为相应的MR探测灵敏度的大幅提高。这样就可以进行各种各样的新颖实验和方法，否则这些实验和方法是不可能实现的。产生高压气体的主要方法之一是自旋交换光泵浦（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稀有气体的核自旋。允许原子核自旋极化随时间累积。令人惊讶的是，SEOP背后的基本物理过程是多方面和相互依存的，尽管对这些过程的光学、原子和分子物理学进行了数十年的研究，但它们尚未得到充分的探索；的确，有很多东西是不知道或不理解的。特别是当SEOP在与MR应用最相关的关键制度和实验条件下进行时。拟议研究的目标是对涉及选定碱金属和稀有气体的SEOP过程有更深入的基本了解，并应用这些见解来改进需要大量高自旋极化气体的MR应用的SEOP。拟议的研究将涉及SEOP，使用铷（Rb）和铯（Cs）作为碱金属，氙-129 （129Xe）和氪-83 （83Kr）作为惰性气体（有可能扩展到131Xe）；虽然Rb/129Xe SEOP在过去已经得到了很好的表征（尽管不是在本工作提出的条件下），但涉及Cs/129Xe的研究以及提高四极性83Kr/131Xe同位素的极化和MR应用的努力仍在很大程度上处于起步阶段。主办机构提出的基本SEOP过程的研究包括：碱金属电子自旋极化（PRb/PCs）分布图的依赖性；利用电子自旋共振（ESR）光谱学对惰性气体类型和密度、电池温度、总压、激光通量、光谱偏移等进行研究；利用拉曼光谱测量氮气的旋转振动温度，研究OP细胞内的能量传输机制（作为相同参数的函数）；并通过低场三维磁共振成像研究OP细胞中相应的核自旋极化分布（和气体动力学）。诺丁汉的仪器？PI将帮助完成哪些？将首次允许实时比较所有这些实验观测值。这些实验不仅将提供有关SEOP的新知识，而且将为MR应用产生高压气体的条件优化提供信息。包括提出的实验，将探索使用高自旋极化气体探测多孔材料和表面。虽然拟议的研究本质上是基础性的，但结果呢？在会议报告和出版物中广泛传播？应对高压气体的新出现和已确立的应用产生直接影响；这些应用是多方面的，从材料研究到肺空间和组织的临床人类磁共振成像。诺丁汉大学凭借其在最先进的实验仪器、专家人员和MR创新方面的悠久历史方面的巨大资源，在担任东道主方面处于独特的地位。提供重要的培训和经验，以及建立长期的国际合作，这将在他的专业研究生涯中对PI产生积极影响。

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.