The helicity-flip and helicity-nonflip scattering amplitudes of a Dirac particle with spin 1/2 and charge $Ze$ by a fixed magnetic monopole field are calculated. To make the Hamiltonian meaningful an infinitesimal extra magnetic moment is added to the charged particle. The sign of this extra term has measurable consequences. The differential cross section, which is independent of the sign of $Ze$, is tabulated. The helicity-flip amplitude vanishes at all angles for incoming beam helicity = +1 if $Zeg>0$, and for incoming beam helicity = -1 if $Zeg<0$.

• Received 17 November 1976

DOI:https://doi.org/10.1103/PhysRevD.15.2287