Use of the CATIA Geometry Description with Geant4 Geometry Package used in ATLAS Cavern Background Simulation
Collaborative partners:  Stanford University;  SLAC

Reliable calculation of cavern background depends on the geometry and material descriptions in the application. There are known deficiencies in the present implementation such as in Barrel End Cap gap region, where the current model does not contain any service and support structures. The work involves developing Geant4 code for the following.

• The missing geometry volumes have to be added using CATIA for envelop dimensions.
• Internal geometry and material description not present in 3D CATIA models have to rebuilt from corresponding 2D drawings.
• The descriptions have to be simplified as appropriate to achieve reasonable computational speed without compromising the physics performance.

Geometry volumes to be addressed after the gap region will be guided by the results of data and simulation comparisons. Possibilities include:
1) Middle Services – services going along End Cap including cable trays with boxes and supports and pipes on both sides A and C
2) JM Shielding