Geant4 Version: 11.03
Operating System: Debian 12.0
Hello everyone,
I wanted to ask if there is way to add radioactive decays to the properties of a material defined in the detector construction. If not is there a way to start the particle gun only inside a specific volume?
Thank you for your help.
No, this isn’t how it’s done in Geant4. Materials aren’t “particles” – they form the static, unchanging universe that particles travel through 
Your second question has it right: you create a G4Ions particle of your radioisotope, and let Geant4 do the decay.
If you use G4GeneralParticleSource (/gps/... commands) instead of plain G4ParticleGun, there is an option to confine the source to a specific volume.
Thank you very much. You were a great help!