NMR, Nuclear & Electron magnetic moments

In summary, the conversation revolves around the understanding of Nuclear Magnetic Resonance (NMR) and its relationship with the magnetic moments of electrons and nuclei. The speaker is having trouble differentiating between the influence of these two moments on NMR and is seeking clarification. They also mention the role of magnetism in NMR experiments and the difference in magnetic dipole moments between electrons and nucleons. The solution is suggested to lie in the fact that NMR pulse routines only act on nuclear moments due to the significantly different Larmor frequencies of electrons and protons, as well as the faster decay of electronic moments due to thermal interactions. The relative strength of the NMR signal from substances with different hydrogen densities also supports this idea.
  • #1
Quattro
9
0
I have got myself very confused. I am trying to understand Nuclear Magnetic Resonance but am running into issues.

The basic idea of NMR, resonant excitations between Zeeman split nuclear energy states, I understand. The semi-classical picture of precessing moments also makes some sense to me.

I think basically I am having trouble distinguishing between the influence of the nuclear and electron magnetic moments on NMR. In a recent course on magnetism, we were taught all about para/dia/ferromagnetism etc. The basic conclusion I now make is that magnetism is related to the moment of the electron itself, or due to its orbit, NOT the nucleus. But that is where I get lost. If magnetism is defined as the alignment of electronic or atomic moments, where do nuclear moments fit in? Aren't NMR experiments supposed to manipulate NUCLEAR moments?

I’m finding it hard to explain exactly what I’m having trouble with, but if anyone can see what I’m grasping at, or has an idea of a possible mistake in my understanding, please post. Maybe this will help me to explain what I think further.

Thanks in advance
 
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  • #2
Ok, quick after thought.

Does the solution lie in the fact that although the magnetising field acts on both moments, subsequent NMR pulse routines etc, are at frequencies so as to only act on the nuclear moments? The magnetic dipole moments of nucleons and electrons are significantly different...
 
  • #3
Quattro said:
Does the solution lie in the fact that although the magnetising field acts on both moments, subsequent NMR pulse routines etc, are at frequencies so as to only act on the nuclear moments?
That would be part of my guess. The Larmor frequency of the electron should, naively, be on the order of 1000 times greater than the Larmor frequency of the proton.

I would also suggest that, since electrons are on the outside of the atom, they interact with other electrons more readily, whereas the nuclei are much more isolated from each other. So, probably the electronic moments decay more rapidly due to their thermal interactions with each other, and the lasting signal that is picked up is that from the longer decay of the protons. This notion is further supported by the relative strength of the signal from water compared to substances with less hydrogen density.
 

Related to NMR, Nuclear & Electron magnetic moments

1. What is NMR?

NMR stands for Nuclear Magnetic Resonance. It is a technique used in chemistry and physics to study the chemical and physical properties of atoms and molecules.

2. How does NMR work?

NMR relies on the principle of resonance, where certain atomic nuclei have a property called spin, which causes them to behave like tiny magnets. In an NMR experiment, a sample is placed in a strong magnetic field and then bombarded with radio waves. The nuclei in the sample absorb energy from the radio waves, causing them to resonate at a specific frequency. By measuring this resonance, we can gather information about the structure and properties of the sample.

3. What are nuclear and electron magnetic moments?

Nuclear and electron magnetic moments are physical quantities that describe the magnetic properties of atomic nuclei and electrons, respectively. They are a measure of how strongly a nucleus or electron interacts with a magnetic field.

4. What are some applications of NMR?

NMR has a wide range of applications in chemistry, physics, and biochemistry. It is commonly used in structural determination of molecules, identifying chemical compounds, and studying molecular dynamics. NMR is also used in medical imaging techniques such as MRI (Magnetic Resonance Imaging).

5. What is the difference between NMR and MRI?

NMR and MRI are both based on the same principles of nuclear magnetic resonance. However, NMR is used to study the properties of molecules in a laboratory setting, while MRI is used for medical imaging purposes. Additionally, MRI uses much stronger magnetic fields and more complex techniques to create detailed images of tissues and organs in the body.

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