  Geant4 is a toolkit for the simulation of the passage of particles through
matter. It provides a comprehensive set of tools for geometry, tracking,
detector response, run, event and track management, visualization and user
interfaces. Geant4 also has an abundant set of physics models that handle the
diverse interactions of particles with matter across a wide energy range.
However, there are also many well-established reaction codes currently used in
the same fields where Geant4 is applied. In order to take advantage of these
codes, we began to investigate their use from within the framework of Geant4.
The first codes chosen for this investigation were the Jaeri Quantum Molecular
Dynamics (JQMD) and Jet AA Microscopic Transportation Model (JAM) codes. JQMD
is a QMD model code which is widely used to analyze various aspects of heavy
ion reactions. JAM is a hadronic cascade model code which explicitly treats all
established hadronic states, including resonances with explicit spin and
isospin, as well as their anti-particles. We successfully developed interfaces
between these codes and Geant4. These allow a user to construct a detector
using the powerful material and geometrical capabilities of Geant4, while at
the same time implementing nuclear reactions handled by the JQMD and JAM models
and the Hadronic framework of Geant4 proved its flexibility and expandability.
