The spin magnetic moment of a charged, spin-1/2 particle that does not possess any internal structure (a Dirac particle) is given by μ μ = g e 2 m S , where μ is the spin magnetic moment of the particle, g is the g -factor of the particle, e is the elementary charge, m is the mass of the particle, and S is the spin angular momentum of the particle (with magnitude ħ /2 for Dirac particles).