Orbital gyromagnetic factor

The gyromagnetic factor is twice as large as that appearing in the relation between the electron orbital angular momentum L and the associated magnetic dipole moment ... 

The values for the atomic saturation magnetization at the absolute zero, ferromagnetic metals iron, cobalt, and nickel are 2.22, 1.71, and 0.61 Bohr magnetons per atom, respectively.9 These numbers are the average numbers of unpaired electron spins in the metals (the approximation of the g factor to 2 found in gyromagnetic experiments shows that the orbital moment is nearly completely quenched, as in complex ions containing the transition elements). 

Since in nuclear physics the mutual orientation of the angular and magnetic moments can be both parallel or antiparallel, the gyromagnetic ratio can also be positive (parallel orientation of these two vectors) and negative (antiparallel orientation as for orbital electron state). Therefore, the nuclear g-factor (g ) (in units e/2 jp) can have both positive and negative signs. They cannot be calculated but are defined from experiment only. Therefore, one can see that the sign is historically casual. For proton gp is +5.5851, for neutron gj,=-1.9103. 

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