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Nuclear Overhauser Enhancement (NOE)01:07

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Irradiation of a spin-active nucleus causes an increase or decrease in the signal intensity of neighboring nuclei that are not necessarily chemically bonded or involved in J-coupling.  This phenomenon, called the Nuclear Overhauser Enhancement (NOE), results from through-space interactions between the nuclear spins. The NOE effect decreases with increasing internuclear distance and is generally not observed beyond 4 angstroms. In NOE, dipole-dipole interactions between neighboring...
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Atomic Nuclei: Nuclear Relaxation Processes01:23

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In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis,  the precessing magnetic moments are randomly oriented around the z-axis.
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Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

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Near absolute zero temperatures, in the presence of a magnetic field, the majority of nuclei prefer the lower energy spin-up state to the higher energy spin-down state. As temperatures increase, the energy from thermal collisions distributes the spins more equally between the two states. The Boltzmann distribution equation gives the ratio of the number of spins predicted in the spin −½ (N−) and spin +½ (N+) states.
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NMR-active nuclei have energy levels called 'spin states' that are associated with the orientations of their nuclear magnetic moments. In the absence of a magnetic field, the nuclear magnetic moments are randomly oriented, and the spin states are degenerate. When an external magnetic field is applied, the spin states have only 2 + 1 orientations available to them. A proton with = ½ has two available orientations. Similarly, for a quadrupolar nucleus with a nuclear spin value of...
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All atomic nuclei are positively charged. When they have a nonzero spin, they behave like rotating charges. As a consequence of their charge and spin, these nuclei generate a magnetic field (B). This, in turn, gives rise to a magnetic moment (μ), which is randomly oriented in the absence of an external magnetic field. When an external magnetic field (B0) is applied, the magnetic moment vectors can align with the field or against it in 2 + 1 orientations. A hydrogen nucleus, which is just a...
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The difference between the calculated and experimentally measured masses is known as the mass defect of the atom. In the case of helium-4, the mass defect indicates a “loss” in mass of 4.0331 amu – 4.0026 amu = 0.0305 amu. The loss in mass accompanying the formation of an atom from protons, neutrons, and electrons is due to the conversion of that mass into energy that is evolved as the atom forms. The nuclear binding energy is the energy produced when the atoms’ nucleons...
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零场重整器动态核极化

Seong-Joo Lee1, Kwon Kyu Yu2, Seong-Min Hwang1

  • 1Quantum Magnetic Sensing Group, Korea Research Institute of Standards and Science, Daejeon 34113, Republic of Korea.

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概括
此摘要是机器生成的。

这项研究使用Overhauser动态核极化 (O-DNP) 在接近零的磁场上演示了超极化水. 这种新方法使用循环偏振射频场显著提高了O-DNP的效率.

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科学领域:

  • 磁共振
  • 物理化学
  • 生物物理

背景情况:

  • 超频动态核极化 (O-DNP) 通常需要显著的磁场进行超极化.
  • 氧基通常用于诱导液体中的超极化.

研究的目的:

  • 用O-DNP在有效的零磁场上演示水的实验超极化.
  • 在O-DNP中研究循环偏振射频 (RF) 场的效率.

主要方法:

  • 使用直角射频线圈产生的循环极化射频场来诱导选择性和.
  • 使用电子对核光谱映射记录2nT的电子磁共振光谱.
  • 使用循环极化射频与线性极化射频对比O-DNP的效率.

主要成果:

  • 在接近零磁场时通过O-DNP实现了水的超极化.
  • 通过选择性和来规避同时出现的正极和负极的有害影响.
  • 与线性极化射频相比,循环极化射频的O-DNP效率增加了超过10倍.
  • 在低于2nT的磁场中记录了氧化基的EPR光谱.

结论:

  • 在接近零的磁场下使用O-DNP可以有效地超极化水.
  • 循环极化射频场显著提高低场的O-DNP效率.
  • 消除了对低场O-DNP的辅助技术的需求,如样本转移或现场循环.