  We examine the spatial distribution of electrons generated by a fixed energy
point source in uniform, parallel electric and magnetic fields. This problem is
simple enough to permit analytic quantum and semiclassical solution, and it
harbors a rich set of features which find their interpretation in the unusual
and interesting properties of the classical motion of the electrons: For
instance, the number of interfering trajectories can be adjusted in this
system, and the turning surfaces of classical motion contain a complex array of
singularities. We perform a comprehensive analysis of both the semiclassical
approximation and the quantum solution, and we make predictions that should
serve as a guide for future photodetachment experiments.
