I have just started studying MRI physics and was reading F.Bloch’s paper on Nuclear Induction.
In page 463, it is mentioned,
To obtain this variation does not require the solution of the Schroedinger equation. It is enough to remember the general fact that the quantum-mechanical expectation value of any quantity follows in its time dependence exactly the classical equations of motion and that the magnetic and angular momenta of each nucleus are parallel to each other.
The parallelity between the magnetic moment $\mu$ and the angular momentum a for each nucleus implies $\mu = \gamma a$
Are the magnetic and angular momenta of the proton always parallel to each other?
Why is this so?