proton magnetic moment flip angle 54.7 in an external magnetic fieldby mkj Tags: angle, field, flip, magnetic, magnetic moment, moment, precession, proton 

#1
Nov2713, 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 



#2
Nov2713, 04:21 PM

Sci Advisor
HW Helper
Thanks
P: 26,167

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 P_{z} is quantised, and (for a spinhalf particle) must be P/√3 so the angle between P and z must be cos^{1}1/√3, = 54.74° (see eg http://www.chem.wisc.edu/areas/reich...hmr00nmr.htm) 


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