  The Dirac equation in $\mathbb{R}^{1,3}$ with potential Z/r is a relativistic
field equation modeling the hydrogen atom. We analyze the singularity structure
of the propagator for this equation, showing that the singularities of the
Schwartz kernel of the propagator are along an expanding spherical wave away
from rays that miss the potential singularity at the origin, but also may
include an additional spherical wave of diffracted singularities emanating from
the origin. This diffracted wavefront is 1-0 derivatives smoother than the main
singularities and is a conormal singularity.
