  Context. The primary energy release in solar flares is almost certainly due
to magnetic reconnection, making this a strong candidate as a mechanism for
particle acceleration. While particle acceleration in 2D geometries has been
widely studied, investigations in 3D are a recent development. Two main classes
of reconnection regimes at a 3D magnetic null point have been identified: fan
and spine reconnection Aims. Here we investigate particle trajectories and
acceleration during reconnection at a 3D null point, using a test particle
numerical code, and compare the efficiency of the fan and spine regimes in
generating an energetic particle population. Methods. We calculated the time
evolution of the energy spectra. We discuss the geometry of particle escape
from the two configurations and characterise the trapped and escaped
populations. Results. We find that fan reconnection is less efficent than spine
reconnection in providing seed particles to the region of strong electric field
where acceleration is possible. The establishment of a steady-state spectrum
requires approximately double the time in fan reconnection. The steady-state
energy spectrum at intermediate energies (protons 1 keV to 0.1 MeV) is
comparable in the fan and spine regimes. While in spine reconnection particle
escape takes place in two symmetric jets along the spine, in fan reconnection
no jets are produced and particles escape in the fan plane, in a ribbon-like
structure.
