Questions tagged [nuclear-magnetic-resonance]

For questions about Nuclear Magnetic Resonance

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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 ...
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1answer
81 views

Mathematical term for the on/off gradient functions in MRI imaging

The slice selection gradients, as well as the phase and frequency, in MRI imaging are traditionally represented by on/off box or rectangular symbols: or My question is what is the mathematical name ...
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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 ...
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is room temperature quantum (qubit) nuclear magnetic resonance possible?

I know it is possible to do room temperature NMR. Not just that but one can also use the earth's magnetic field for the nuclei to precess about. If done this way, one gets precession at about the KHz ...
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13 views

$j$-$j$ coupling interaction in Magnetic Resonance Spectroscopy

I am studying Magnetic Resonance Spectroscopy and I have some difficulties in understanding the j-j coupling interaction. What does actually happen from the physical point of view to the electronic ...
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2answers
71 views

Do protons and electrons actually precess?

I know that protons and electrons do not actually spin, although they have the property of spin. I was learning about MRI. I was introduced to the idea that you have the spin of the proton in the ...
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1answer
35 views

Why do 180 degree NMR pulses not violate Einsteins laws for absorption and emission?

So, in Laser theory I learned that a two-level laser is not possible, because it would violate Einsteins equations and the Boltzmann distribution, which in a nutshell say that I cannot cause ...
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19 views

Spin-flip of electrons in non-neutral hydrogen atoms in water and fat molecules

What is the Spin-flip of electrons in non-neutral hydrogen atoms in water and fat molecules? I know there is known spin-flip RF of electrons in neutral hydrogen atoms (hydrogen line). Thanks, Cheers
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1answer
37 views

On the origin of spin-lattice relaxation

According to P.J. Hore in the Oxford Chemistry Primer "Nuclear Magnetic Resonance" p57, 'the dipolar coupling, modulated by molecular motions, causes nuclear spins to experience time-dependent local ...
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47 views

MRI T1 contrast and k-space understanding

I have a couple of questions regarding MRI theory; I have read around but am struggling to find and answer and move on in my understanding; as such any help would be much appreciated: When designing ...
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1answer
41 views

Origin of 2π normalization factor in chemical $J$-coupling compared to the Heisenberg model

In chemistry, particularly the field of NMR spectroscopy, the interaction between two (nucleic) spins (or so I guess?) is governed by the Hamiltonian: \begin{align} \mathcal{H}=2\pi\cdot J_{ij}{\vec {...
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1answer
321 views

Spin precession for Rabi oscillations : interpretation with magnetic field in rotating frame

The model considered Consider an atom modeled by a two level system of energy $\hbar \omega$. We assume this atom is interacting with an electric field through electric-dipole interaction. The full ...
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21 views

Continuous NMR Coil arrangement and signal generation

So I am trying to understand how a signal is being produced in CW NMR and I cam across this online An it talks about how the in CW the spectrum depends only the current being induced in the x-y plane....
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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 ...
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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{...
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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?
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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 \...
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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 ...
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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 ...
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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 ...
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11 views

Is the amplitude of the RF pulse affects the NMR signal?

What i knew is that the NMR signal depends on the static magnetic field strength $ B_0 $ (by Boltzmann equation) and its gyromagnetic factor. While the NMR occurs when the RF pulse frequency match the ...
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17 views

Magnetic field measured by NMR

I'm trying to understand some old NMR papers on CrCl$_{3}$ and CrBr$_{3}$ (see [1] and [2]). They did continuous-wave, zero-field Cr$^{53}$ NMR spectroscopy on these compounds, which order either ...
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9 views

What affects spin-lattice and spin-spin relaxation times?

I'm performing NMR on common substances like mineral oil, water, and a copper sulfate solution. I know that the ions cause low spin-lattice and spin-spin relaxation times in copper sulfate solution. ...
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18 views

Data augmentation in $k$-Space

I am working on denoising data in $k$-space for MRI (magnetic reasonance imaging) using Convolutional neural networks, and I am wondering what would be some suitable data augmentation techniques ...
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18 views

Ramsey technique and spin echos

Assuming we use a laser of frequency very close to resonance, in the Ramsey technique (say for 2 level atoms) the $\pi/2$ pulse would put the Bloch vector in the equatorial plane, along the y axis, ...
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1answer
27 views

Tip angle in NMR

Tipping the magnetisation $\vec{M}$ with a $\vec{B}_1$ field for the time $\tau$, results in a tip angle of $\alpha = \omega \tau$ where $\omega$ is the frequency of the $\vec{B}_1$ field. I think I ...
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9 views

Was NMR/ESR spin flip-flop line ever measured?

Let $a$,$b$ be two unlike spins in a uniform magnetic field and RF excitation, and let $B_0$ be the magnetic field for which some transition energies of the spins coincide $E_a^{i,j}(B_0)=E_b^{k,l}(...
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9 views

Q-Populations difference using Boltzmann distribution

Question- Calculate the difference in the populations of the two nuclear spin states of $1H$ nuclei in a magnetic field of $10T$ at a temperature of $298K$ Answers to chose from (it’s a multiple ...
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1answer
88 views

Why would giving a 90 degree Radiofrequency pulse to a ZERO longitudinal magnetisation cause zero transverse magnetisation in MRI?

Let's imagine in my scenario the (a) in the picture above has no net longitudinal magnetization (therefore 0 longitudinal). Why would giving an 90° RF pulse in my scenario not cause the Protons to ...
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1answer
11 views

What is responsible for large ppm shifts in HNMR analysis of paramagnetic compounds?

In H-NMR spectra of paramagnetic metal acetylacetonate compounds M(III)(acac)3, large ppm shifts are observed. This is seen with other organometallic compounds as well. What is the origin of this ...
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41 views

Quantum Mechanical Treatment of the Spin Echo

I'm trying to find the expectation value of the spin in the $y$ direction after applying a $\pi/2$-$\pi/2$ sequence of pulses. In Slichter's Principles of Magnetic Resonance, he does a $\pi/2$-$\pi$ ...
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1answer
43 views

What is the true way to determine time parameters from semilog graph?

I have experimental nuclear magnetic resonance data that describe T2-relaxation of the nuclei in the sample of interest. The experimental points obey bi-exponential dependence: I = I1*exp(-t/T2_1) + ...
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29 views

NMR: Link between relaxation time and Chemical shift

I have been taught NMR in both my physics and chemistry high school classes. Everything lines up until they get into how we detect different chemical environments in the compound. Chemistry class: ...
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1answer
33 views

How does an magnetic resonance guided focused ultrasound (MRgFUS) machine work?

As a medical application, magnetic resonance guided focused ultrasound (MRgFUS), is new I the treatment of some parkinsonian diseases, prostate cancer, none problems, and more. However, I am not sure ...
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1answer
27 views

Amplitude of a signal from it's function

If I have the equation of a light pulse in the form $$L(ω)=\frac{1}{π}\frac{\frac{1}{2}Γ}{((ω−ω_0)^2+(\frac{1}{2}Γ)^2)}$$ where $\Gamma$ is the linewidth of the pulse and $\omega_0$ is its resonant ...
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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 ...