The output below is for a 100MeV Proton incident upon a volume of water (using geant4.7.0_p01, QGSP 2.8.1, packaging 2.5.1) ********************************************************************************************************* * G4Track Information: Particle = proton, Track ID = 1, Parent ID = 0 ********************************************************************************************************* Step# X(mm) Y(mm) Z(mm) KinE(MeV) dE(MeV) StepLeng TrackLeng NextVolume ProcName 0 0 0 -1e+04 100 0 0 0 physiSlice0 initStep 1 0.275 -0.0595 -9.98e+03 86.7 13.3 16.7 16.7 physiSlice0 hIoni 2 0.225 -0.309 -9.97e+03 74.7 12 13.4 30.1 physiSlice0 hIoni 3 0.218 -0.471 -9.96e+03 0 6.32 5.98 36.1 physiSlice0 ProtonInelastic :----- List of 2ndaries - #SpawnInStep= 1(Rest= 0,Along= 0,Post= 1), #SpawnTotal= 1 --------------- : 0.218 -0.471 -9.96e+03 12.8 alpha :----------------------------------------------------------------- EndOf2ndaries Info --------------- ********************************************************************************************************* * G4Track Information: Particle = alpha, Track ID = 2, Parent ID = 1 ********************************************************************************************************* Step# X(mm) Y(mm) Z(mm) KinE(MeV) dE(MeV) StepLeng TrackLeng NextVolume ProcName 0 0.218 -0.471 -9.96e+03 12.8 0 0 0 physiSlice0 initStep 1 0.216 -0.548 -9.96e+03 0 12.8 0.162 0.162 physiSlice0 hIoni When the proton undergoes an inelastic collision with the alpha, of the 74.7MeV available: 6.24MeV is deposited in the detector by the proton 12.8MeV is deposited by the alpha This leaves 55.66MeV unaccounted for. Similar events can also be seen using other physics lists (e.g LHEP, and ExN04)
What you describe is probably not a bug. The proton has interacted with an oxygen nucleus and produced an alpha. The remaining 56 MeV could easily be taken up by a combination of: 1) the nuclear binding energy of the target nucleus (could be up to 127 MeV if the nucleus was broken into fragments, but more likely about 30 MeV) 2) the Fermi momentum of the nucleons within the nucleus 3) other inelasticities which are parameterized in the models, but not calculated in detail, such as the excitation energy of the residual nucleus) In your case the residual nucleus was not tracked, so we do not know what it was.
