  We investigate the spatial distribution of charged particles accelerated by
non-relativistic oblique fast collisionless shocks using three-dimensional
test-particle simulations. We find that the density of low-energy particles
exhibit a localised enhancement at the shock, resembling the "spike" measured
at interplanetary shocks. In contrast to previous results based on numerical
solutions to the focused transport equation, we find a shock spike for any
magnetic obliquity, from quasi-perpendicular to parallel. We compare the
pitch-angle distribution with respect to the local magnetic field and the
momentum distribution far downstream and very near the shock within the spike;
our findings are compatible with predictions from the scatter-free shock drift
acceleration (SDA) limit in these regions. The enhancement of low-energy
particles measured by Voyager 1 at solar termination shock is comparable with
our profiles. Our simulations allow for predictions of supra-thermal protons at
interplanetary shocks within ten solar radii to be tested by Solar Probe
Mission. They also have implications for the interpretation of ions accelerated
at supernova remnant shocks.
