Particle tracking in sophisticated CAD models for simulation purposes

The transfer of physics detector models from computer aided design systems to physics simulation packages like GEANT suffers from certain limitations. In addition, GEANT is not able to perform particle tracking in CAD models. We describe an application which is able to perform particle tracking in boundary models constructed in CAD systems. The transfer file format used is the new international standard, STEP. The design and implementation of the application was carried out using object-oriented techniques. It will be integrated in the future object-oriented version of GEANT.