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Proton magnetic moment flip angle 54.7 in an external magnetic field

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mkj
#1
Nov27-13, 03:39 PM
P: 5
i am reading about MRI. i have seen several in several textbooks that the angle between the direction of the proton magnetic moment μ and the direction of the external magnetic field is 54.7
how did they find that theoretical or experimental
if theoretical how can we calculate that
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tiny-tim
#2
Nov27-13, 04:21 PM
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P: 26,148
hi mkj!

loosely speaking, the angular momentum P is fixed

if there's no magnetic field, there's no problem the "spin axis" can be in any direction

if there is a magnetic field in the z direction, the component Pz is quantised, and (for a spin-half particle) must be P/√3

so the angle between P and z must be cos-11/√3, = 54.74

(see eg http://www.chem.wisc.edu/areas/reich...hmr-00-nmr.htm)


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