  Simulating the irradiation of planetary atmospheres by cosmic ray particles
requires, among others, the ability to understand and to quantify the
interactions of charged particles with planetary magnetic fields. Here we
present a process that is very often ignored in such studies; the dispersion
and focusing of cosmic ray trajectories in magnetospheres. The calculations
were performed using our new code CosmicTransmutation, which has been developed
to study cosmogenic nuclide production in meteoroids and planetary atmospheres
and which includes the computation of the irradiation spectrum on top of the
atmosphere. Here we discuss effects caused by dispersion and focusing of cosmic
ray particle trajectories.
