A good powerful simulation tool you should look into should really be GEANT4. It really sets the standard by which all Nuclear Physics simulation try to adhere.

A good powerful simulation tool you should look into should really be GEANT4. It really sets the standard by which all Nuclear Physics simulation try to adhere. It is not a 'toy' but more like a collection of tools you can use to simulate anything from x-ray radiation to a Photon's path inside a scintillator.