Proton magnetic moment flip angle 54.7 in an external magnetic field

  1. mkj

    mkj 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. jcsd
  3. tiny-tim

    tiny-tim 26,043
    Science Advisor
    Homework Helper

    hi mkj! :smile:

    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/nmr/05-hmr-00-nmr.htm)
     
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