Questions tagged [nuclear-magnetic-resonance]

For questions about Nuclear Magnetic Resonance

Filter by
Sorted by
Tagged with
1
vote
0answers
21 views

Effect of a Lorentzian pulse on a non-resonant spin particle

I'm looking into rotation of a nuclear spin particle using a pulse with a Lorentzian lineshape. If the pulse has an area of $\frac{\pi}{2}$ and the nuclear spin frequency is on resonance with the ...
2
votes
2answers
191 views

Why are spins initially coherent after 90 degree pulse in NMR?

In NMR we apply a 90 degree radio frequency pulse to the sample. This causes magnetization vector to fall into transverse plane. Then the relaxation of initial phase coherence occurs. Why are the ...
4
votes
1answer
187 views

How to explain spin-spin relaxation in MRI/NMR in terms of quantum mechanics?

I noticed two approaches to explanation of MRI/NMR. The most popular classical approach exploits the notion of magnetization vector and Larmor precession. Everything then is described as oscillations ...
0
votes
1answer
42 views

Modelling a radiofrequency pulse

I'm looking into NMR at the moment and am trying to work out a way of modelling the action of a radiofrequency pulse on nuclear spins. Specifically, if I apply a pulse to rotate the spin by $\pi/2$ I ...
1
vote
1answer
512 views

Why do nuclei precess in magnetic fields?

I understand that a classical bar magnet will precess about the axis of an external magnetic field. Whilst researching NMR, I have read that nuclei with half-integer spin which are subject to an ...
1
vote
1answer
100 views

Distributive property of tensor product

I have a homework problem in nuclear magnetic resonance. After a bunch of calculations, I have arrived at the expression: $$\langle M_1(t)\rangle = {\rm tr}\left [\rho(0)\sigma_+^{(1)}\exp\left(i\frac{...
0
votes
2answers
662 views

Hyperfine Interaction Hamiltonian

I didn't had any course on hyperfine interactions and now I am having trouble in solving the Anisotropic Hyperfine Hamiltonian. The problem is of matrix dimensions that have to be considered in the ...
1
vote
0answers
52 views

magnetism in NMR spectroscopy

How do electrons reduce the effective magnetic field felt by protons? This is the explanation given to chemical shift, how does it work?
1
vote
0answers
50 views

Nonlinearities arising from linear equations

I have sources that tell me that the Bloch Equations, which describe the magnetization vector in nuclear magnetic resonance, are nonlinear. In vector form, without relaxation, they are: $$ \partial_t \...
1
vote
0answers
42 views

NMR Chemical shift and the electron distribution

We explain the position of a hydrogen environment as being downfield if it is deshielded by its proximity to an electron withdrawing group. The electrons around the nucleus protect said nucleus from ...
2
votes
1answer
50 views

How to excite high spin nuclear state from ground state?

For example, the ground state of a nuclei is $0^+$, and we can excite $1^-$ state with a circular polarized gamma photon, which has a spin angular momentum $1\hbar$. This satisfies the selection rule ...
1
vote
0answers
59 views

is alternating field really needed for NMR/ESR?

Consider a two level system - say a single spin-1/2 electron in a magnetic field. To make transition between the spin-split levels the usual advice is to apply an alternating transverse magnetic field ...
0
votes
1answer
360 views

In Nuclear Magnetic Resonance what is the Rotating Frame?

My understanding is that there's an initial precession frequency ($\omega_0$) about the direction of magnetization ($z$). Then when you excite the nucleus into the spin state with the radio frequency ...
4
votes
0answers
318 views

Good books on NMR

I need some help in finding a good book on NMR spectroscopy that focuses more on the physical aspects of the phenomenon and not so much on the chemical application. All the books I've read on that ...
1
vote
1answer
175 views

Time-domain NMR or: When is the Fourier-Transformation not appropriate?

My question has two parts: One is general and has to do with the Fourier-Transformation, one has to do with Time-Domain NMR. Both parts are interlinked, of course. I tried to find out, why people do ...
18
votes
3answers
1k views

How specifically does an MRI machine build an image from received radio waves?

Unlike the excellent Wikipedia page on ultrasound imaging, the one on MRI only explains the principle theory behind MRI - that oscillating strong magnetic fields cause water molecules to emit ...
2
votes
1answer
1k views

What is Rabi nutation in NMR?

What is the mathematical and physical significance of Rabi Nutation in terms of NMR?
1
vote
1answer
281 views

NMR rotating frame

I'm reading about a linearly polarized field (in the context of NMR). The field is given by $$ {\bf H_{lin}}=2H_1({\bf i}\cos(\omega_zt)).$$ This can be created by having a pulse field plus its ...
11
votes
1answer
509 views

Nuclear Magnetic Resonance (NMR) Conceptual Questions

Let $M$ be the magnetic moment of a system. Below are the Bloch equations, including the relaxation terms. $$\frac{\partial M_x}{\partial t}=({\bf M} \times \gamma {\bf H_0})_x-\frac{M_x}{T_2} $$ $$...
2
votes
0answers
165 views

Correlation function in relaxation in NMR

I am new in this community, I am from a chemistry background. I want to know a detailed solution of a density matrix for a singlet state using the concept of spin lattice relaxation in NMR. I will ...
15
votes
2answers
487 views

Decoherence and measurement in NMR

It seems that the Bloch equations, or a suitable generalization thereof, are enough to phenomenologically model the measurement process in NMR. Has anyone attempted a fully quantum mechanical model ...

1
2