  Bohmian trajectories are considered for a particle that is free (i.e. the
potential energy is zero), except for a half-line barrier. On the barrier, both
Dirichlet and Neumann boundary conditions are considered. The half-line barrier
yields one of the simplest cases of diffraction. Using the exact time-dependent
propagator found by Schulman, the trajectories are computed numerically for
different initial Gaussian wave packets. In particular, it is found that
different boundary conditions may lead to qualitatively different sets of
trajectories. In the Dirichlet case, the particles tend to be more strongly
repelled. The case of an incoming plane wave is also considered. The
corresponding Bohmian trajectories are compared with the trajectories of an oil
drop hopping on the surface of a vibrating bath.
