  We present results of simulations performed with the Geant4 software code of
the effects of Galactic Cosmic Ray impacts on the photoconductor arrays of the
PACS instrument. This instrument is part of the ESA-Herschel payload, which
will be launched in late 2007 and will operate at the Lagrangian L2 point of
the Sun-Earth system. Both the Satellite plus the cryostat (the shield) and the
detector act as source of secondary events, affecting the detector performance.
Secondary event rates originated within the detector and from the shield are of
comparable intensity. The impacts deposit energy on each photoconductor pixel
but do not affect the behaviour of nearby pixels. These latter are hit with a
probability always lower than 7%. The energy deposited produces a spike which
can be hundreds times larger than the noise. We then compare our simulations
with proton irradiation tests carried out for one of the detector modules and
follow the detector behaviour under 'real' conditions.
