/sci Red pill me on NMR Does nucleus really twist and roll while

File: rarest pepe.jpg (41KB, 404x306px) Image search: [Google]

41KB, 404x306px

>>8221213
>I am a chemist trying to understand Physics

well there's your first problem right there

You can only measure with complete accuracy the total angular momentum and the projection of the angular momentum on a single axis. This is called a complete set of commuting observables.

It's debateable whether or not it's "actually spinning" but it has the algebra of angular momentum, so it's just called spin regardless. You can think of it as like left and right handed polarization.

>>8221213
>Red pill me on NMR
Rotating magnetic fields cause the dipole moment of the nucleus to flip back and force at a particular frequency. This causes it to radiate when it flips to a state that is parallel to an established (static) magnetic field. In MRI machines, this static field is given a gradient so that the radiation's energy (which varies with the field) can be analyzed and the nucleus that radiated it can be located. The emission rate is only high near a chosen resonance frequency, so usually this is set so only particular nuclei resonant. Perhaps oxygen, so you can see where water is in the body.

>Does nucleus really twist and roll while precessing or it is just a figure of speech?
No it doesn't do that. Take hydrogen for example: in the reference frame of the atom, the orbital angular momentum belongs to the electron. The electron has spin and so does the proton (and neutron). The word "spin" is in retrospect a horrible choice for this phenomenon, but it's much too late. The proton has a non-spatial degree of freedom that can be completely described by two quantum numbers: the total spin, and the projection of that spin on some given axis (as the other anon mentioned). The reason why that quantum state produces a real magnetic field is a complicated question and involves calculating things in QED. Just know that it does, just as how the parameter of electric charge creates a real electric field in the reference frame of the particle.

Nothing is actually spinning. The quantum state of the electron or proton interacts with the electromagnetic(photon) field in such a way that the electron exists with a permanent magnetic dipole of a constant strength. Hence in a strong external field, you can break the symmetry associated with the orientation of the dipole and create energy gaps. External influence on the dipole changes the quantum state (the projection of the spin) and causes it to "flip" back and forth as if the whole nucleon were somehow rotating.

>>8221377
I think the whole thing is a spin off from describing certain analytical techniques that rely on vibration of the molecule to observe mass to charge ratio. When I learnt about all this in chem, they were taught hand in hand

File: back-to-pol.jpg (35KB, 490x290px) Image search: [Google]

35KB, 490x290px

>>8221213
>Red pill me
GTFO

>>8221843
Sorry for my lame humor. I know I should not try to be entertaining as English is my second language.
No offense intended tho.

>>8221250
Actually I am educated as a pharmacist and now working as a coder. There are guys in our lab always ready to answer questions but I don`t feel like asking something basic from Wikipedia. Understanding of the process is not crucial for me, I am just a number cruncher, it is mostly my curiosity

File: image007.jpg (10KB, 304x298px) Image search: [Google]

10KB, 304x298px

>>8221321
That`s my problem. I can`t get which vector projected on which axis.

>>8221377
Nice answer, anon, I appreciate.
So, spin is some categorical state of electron or other particle but nucleus is literally rolling in space?
It is true I don`t want to touch any quantum stuff, basic Physics is more than enough for me already.

>>8221213
No it's not. Spin is just a terrible name for a phenomenon that arises from the freedom of choice of quantum numbers. However, in my theoretical chemistry lecture, it seemed like you can treat the quantum spin just like the "classical" one to the most extend. Just see it as some kind of way to discretise some aspects of the rather complex QM.

>>8223192
I will senpai
I feel better knowing I am going to be fine using just simple mechanistic vector stuff.
Just not sure still about that 'projection of angular momentum on axis'. I read wiki and shit a lot but can't get this.
In my understanding vector is straight, has a direction and a scalar. But the sum of all angular vectors looks like zero. Or is it projection of precessing divergence to the axis of nucleus in the base magnetic field?
Sorry for my stupidity but I am really curious and trying to get it.