GOALI: Resolving Outstanding Questions in Spin-Exchange Optical Pumping of 129Xe

GOALI：解决129Xe自旋交换光泵浦中的突出问题

• 批准号: 2110608
• 负责人: Brian Saam
• 金额: $ 47.95万
• 依托单位: Washington State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2110608&HistoricalAwards=false
• 关键词: GOALI; Resolving; Outstanding; Questions; Spin

General audience abstract:One of the many atomic properties discovered at the start of the first quantum revolution in the early twentieth century is spin. Spin causes some atomic particles (e.g., electrons, protons, and many atomic nuclei) to behave like spinning magnets. Much the way rotating magnets produce currents in a nearby coil (as with hydroelectric power), samples of atoms possessing spin, if the magnets are all aligned together (``polarized”), can be detected and manipulated with a nearby coil of wire. The PI uses “optical pumping,” a process involving lasers that transfers spin from light to rubidium or cesium atoms, which then collide with xenon atoms to create samples of spin-polarized xenon nuclei. The activities and goals in this project are centered on understanding and maximizing the efficiency of spin transfer to xenon nuclei. The PI’s GOALI partner, Polarean, Inc. (Durham, North Carolina), engineers and markets xenon polarizers, which can be used in magnetic resonance imaging (MRI), particularly of the human lung. MRI normally relies on the presence of water in human tissues to produce an image, but there is very little water in the gas space of the lung. Xenon gas is non-toxic and is not metabolized by the body, but the spin polarization causes the gas to “light up” on an MRI the same way that water does in other tissues. This technique has enormous potential to answer important questions about lung function and lung disease (the fourth leading cause of death in the United States) but making the technique reliable and cost-effective depends on the work done in this project to understand the physics of spin transfer. Beyond this application, spin is playing an important role in the ongoing second quantum revolution, where we now speak of “spintronics” (the spin version of electronics), and spin properties have become important in implementations of quantum computing and related technologies. Students are “hands-on” in the lab learning electronics, vacuum technology, plumbing, and even some glass blowing; they are technically well trained but also come out in possession of skills that can serve them in a host of other occupations, both in and outside of the academy. Promoting equity, diversity, and inclusion in the laboratory environment is a goal. Historically about half of the undergraduate researchers in the group have been women. This project will also both complement and benefit from a newly awarded departmental NSF-REU project. Technical audience abstract:The stable spin-1/2 isotopes 3He and 129Xe are readily hyperpolarized (HP) to levels exceeding 10% via spin-exchange optical pumping (SEOP). SEOP of 129Xe is of particular interest because it is both less well understood and likely to supersede 3He as the nucleus of choice for noble-gas MRI. Together with the GOALI partner, Polarean, the PI seeks both to address persistent yet critical physics issues in SEOP of 129Xe and to implement this knowledge in a commercial polarization device. The three main research aims are: 1) Measurement of Rb and Cs spin destruction due to Xe in the less-studied regime of low Xe partial density and low total gas density (tens of torr and below). 2) Measurement of 129Xe spin-exchange rates at low gas densities for both Rb-129Xe and Cs-129Xe in the same low-density regime as in Aim 1, where van der Waals molecules have longer lifetimes and spin-exchange times should be fast (minutes to seconds). Together, Aims 1 and 2 allow determination of the spin-exchange efficiency, the crucial figure of merit for evaluating efficient production of HP gases. The project also aims to characterize “hybrid” cells, containing both Rb and Cs, to determine whether specific vapor-pressure ratios optimize SEOP efficiency. 3) Search for direct evidence of the presence of alkali-metal nanoclusters in a SEOP polarizer, incorporate their effects into the “standard model” for hyperpolarized 129Xe production, and begin to develop strategies to eliminate them or mitigate their effects. The main experimental approach is EPR spectroscopy of the alkali-metal atoms using Faraday rotation, whereby two specific techniques have been developed: a cw “frequency locking” technique to measure the polarized 129Xe magnetic field, and a pulsed technique (analogous to pulsed NMR) to rapidly acquire the entire hyperfine spectrum.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.

在世纪初第一次量子革命开始时发现的许多原子性质之一是自旋。自旋导致一些原子粒子（例如，电子、质子和许多原子核）的行为就像旋转的磁铁。 就像旋转的磁铁在附近的线圈中产生电流一样（就像水力发电一样），如果磁铁都排列在一起（“极化”），就可以用附近的线圈检测和操纵具有自旋的原子样本。PI使用“光泵浦”，这是一个涉及激光的过程，它将光的自旋转移到铷或铯原子上，然后与氙原子碰撞，产生自旋极化的氙原子核样品。 这个计画的活动和目标是集中在了解和最大化自旋转移到氙原子核的效率。PI的GOALI合作伙伴Polarean，Inc.（达勒姆，北卡罗来纳州），设计和销售氙偏振器，其可用于磁共振成像（MRI），特别是人肺的磁共振成像。MRI通常依赖于人体组织中存在的水来产生图像，但肺的气体空间中几乎没有水。氙气是无毒的，不会被身体代谢，但自旋极化会导致气体在MRI上“发光”，就像水在其他组织中一样。 这项技术具有巨大的潜力来回答有关肺功能和肺部疾病（美国第四大死因）的重要问题，但使该技术可靠且具有成本效益取决于该项目所做的工作，以了解自旋转移的物理学。除了这个应用，自旋在正在进行的第二次量子革命中发挥着重要作用，我们现在所说的“自旋电子学”（电子学的自旋版本），自旋性质在量子计算和相关技术的实现中变得重要。学生在实验室学习电子，真空技术，管道，甚至一些玻璃吹制“动手”;他们在技术上训练有素，但也掌握了可以在学院内外的许多其他职业中为他们服务的技能。促进实验室环境的公平、多样性和包容性是一个目标。从历史上看，该小组中约有一半的本科研究人员是女性。该项目还将补充和受益于新授予的部门NSF-REU项目。技术观众摘要：稳定的自旋1/2同位素3 He和129 He通过自旋交换光泵浦（SEOP）很容易超极化（HP）到超过10%的水平。129 He的SEOP特别令人感兴趣，因为它既不太好理解，也可能取代3 He作为惰性气体MRI的选择核。与GOALI合作伙伴Polarean一起，PI寻求解决129 ° SEOP中持续存在但关键的物理问题，并在商业偏振设备中实现这些知识。主要的研究目标有三个：1）在研究较少的低氘分密度和低总气体密度（几十氘以下）区域测量由于氘的Rb和Cs自旋破坏。2)在与目标1相同的低密度状态下，测量Rb-129 He和Cs-129 He在低气体密度下的129 He自旋交换率，其中货车德瓦耳斯分子具有较长的寿命，自旋交换时间应该很快（分钟到秒）。目标1和2一起允许确定自旋交换效率，这是评估HP气体的有效生产的关键品质因数。该项目还旨在表征含有Rb和Cs的“混合”电池，以确定特定的蒸汽压力比是否优化SEOP效率。3)寻找碱金属纳米团簇在SEOP偏振器中存在的直接证据，将它们的影响纳入超极化129氘生产的“标准模型”，并开始开发消除它们或减轻它们影响的策略。主要的实验方法是使用法拉第旋转的碱金属原子的EPR光谱，由此开发了两种特定的技术：测量极化129 Ω磁场的CW“频率锁定”技术，和脉冲技术（类似于脉冲NMR）该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的学术价值和更广泛的影响审查标准。

项目成果

Collisional electron paramagnetic resonance frequency shifts in Cs-Rb-Xe mixtures

Cs-Rb-Xe 混合物中的碰撞电子顺磁共振频移

• DOI: 10.1103/physreva.106.012801
• 发表时间: 2022
• 期刊: Physical Review A
• 影响因子: 2.9
• 作者: Zou, S.;Morin, D. J.;Weaver, C.;Armanfard, Z.;Muschell, J.;Nahlawi, A. I.;Saam, B.
• 通讯作者: Saam, B.