Larmor frequency definition

Larmor frequencies are typically of 500 MHz for a proton immersed in a static magnetic field of amplitude 5 = 12 T, a very strong, but nowadays current magnetic field. In the same magnetic field, the Larmor frequency of a fluorine nucleus F is a bit smaller, that of a carbon atom that represents more than 99% of all C-atoms in natural conditions has no spin and is consequently not directly seen in NMR) is four times smaller and that of a N about 0.07 that of the proton. This first approximation consequently allows us to define various ranges of radiofrequencies to be used to induce transitions between spin levels of a definite nucleus, H, F, N, N, etc. 

In the current loop definition the magnetic moment, fi, is defined as the product of the electric current I with the area A that the current loop encloses. Within the Bohr atomic model, the electric I current is determined by the number Z and the Larmor frequency (to = eRjlm) of the electrons orbiting around the nuclei. 

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