  The full-energy-peak efficiency of HPGe detectors at $\gamma$-ray energies
around 10 MeV is not easily accessible with experimental methods. Monte-Carlo
simulations with Geant4 can provide these efficiencies. G4Horus is a
ready-to-use Geant4 application for the HORUS HPGe-detector array. Users can
configure the modular parts to match their experiment with minimal knowledge of
the simulation software and limited time commitment. In our case, knowing and
implementing the geometry with high precision is the biggest challenge. To
implement the different target chambers, we transform the existing CAD models
to Geant4 geometry with CADMesh. We also found a large discrepancy between
experimental and simulated efficiency for some older HPGe detectors, which
could be remedied by introducing a large dead region around the inner core.
This project is open source and available from
https://github.com/janmayer/G4Horus We invite everyone to adapt the project or
adopt parts of the code for other projects.
