Some Geant4 physics models require cross section data files. The locations of these datasets is specified by environment variables.
G4LEVELGAMMADATA G4RADIOACTIVEDATA NeutronHPCrossSections G4LEDATA G4ELASTICDATA
The datasets can be obtained from the Geant4 downloads area.
Here is an example bash script for setting up these environment variables, assuming that the data files were downloaded and unpacked to the (fake) directory /path/to/data.
#!/bin/sh G4DATA=/path/to/data/ export G4LEVELGAMMADATA=$G4DATA/PhotonEvaporation2.0 export G4RADIOACTIVEDATA=$G4DATA/RadioactiveDecay3.1 export NeutronHPCrossSections=$G4DATA/G4NDL3.10 export G4LEDATA=$G4DATA/G4EMLOW4.1 export G4ELASTICDATA=$G4DATA/G4ELASTIC1.1