NMR at Low Temperatures

低温核磁共振

• 批准号: 8711907
• 负责人: John Waugh
• 金额: --
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing grant
• 财政年份: 1987
• 资助国家: 美国
• 起止时间: 1987-09-01 至 1995-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=8711907&HistoricalAwards=false
• 关键词: NMR; Low; Temperatures

Nuclear Magnetic Resonance (NMR) spectroscopy is uniquely important to almost every modern scientific discipline. It provides definitive structural data for simple molecules as well as complex biologically important systems. Unlike other spectroscopies, however, NMR suffers from conspicuously low sensitivity--partly because of the low energy of the (radiofrequency) photons involved, but more importantly from the small polarizations of nuclear spin systems. The Boltzmann factor appropriate to typical magnetic moments in a laboratory Zeeman field at room temperature leads to a fractional excess population in the absorbing state on the order of 0.0001 to 0.00001. The history of NMR is replete with technical advances which attack this problem by increasing the applied magnetic field, but the current state of the physics and engineering underlying magnet design offer little hope for any further large improvements in the near future. It is the goal of the research in Professor Waugh's laboratory to obtain significant improvements (10,000 to 100,000) in signal by lowering the temperature. The gains to be made are potentially remarkable: at high temperatures the polarization and hence the voltage sensitivity grow directly as 1/T, suggesting potentially unlimited gains through arbitrarily close approaches to T=O. This is a high risk research program as it is technically very difficult to operate NMR equipment in the millikelvin range. However, the payoff to all NMR justifies the effort.

核磁共振波谱学对几乎所有现代科学学科都具有独特的重要性。它为简单分子和复杂的重要生物系统提供了明确的结构数据。然而，与其他光谱学不同，核磁共振的灵敏度明显较低——部分原因是所涉及的（射频）光子能量较低，但更重要的是，核自旋系统的极化很小。适用于室温下实验室塞曼场中典型磁矩的玻尔兹曼因子导致在0.0001至0.00001量级的吸收态的分数过剩人口。核磁共振的历史充满了通过增加应用磁场来解决这个问题的技术进步，但目前的物理和工程基础磁体设计的现状在不久的将来没有任何进一步的大改进的希望。Waugh教授实验室的研究目标是通过降低温度获得显著的信号改善（1万到10万）。获得的增益可能是显著的：在高温下，极化和电压灵敏度直接增长为1/T，表明通过任意接近T=O可能获得无限增益。这是一个高风险的研究项目，因为在毫开尔文范围内操作核磁共振设备在技术上非常困难。然而，所有NMR的回报证明了这种努力是值得的。