  Particle induced X-ray emission (PIXE) is an important physical effect that
is not yet adequately modelled in Geant4. This paper provides a critical
analysis of the problem domain associated with PIXE simulation and describes a
set of software developments to improve PIXE simulation with Geant4. The
capabilities of the developed software prototype are illustrated and applied to
a study of the passive shielding of the X-ray detectors of the German eROSITA
telescope on the upcoming Russian Spectrum-X-Gamma space mission.
