G3 to G4
Ionisation by charged hadron

Total cross section, Mean free path, dE/dX table, constraint

• Geant3
  S(E,Z,Tcut): knock-on electron cross section, applicable for I < < T
  (I: mean excitation energy of the material; T: kinetic energy of the d-ray).
  dE/dX (E,Z,Tcut): Bethe-Bloch formula above 2 MeV, simple parameterisation below 2 MeV.
  reasonable behaviour below 10 keV. ---> 100 eV - 100 MeV plot
  Step limitation due to energy loss.
  

• Geant4 standard
  Adapted from Geant3
  Improved algorithm for the step limitation due to energy loss.
  Alternative: Photo Absorption Ionisation model.
  

• Geant4 low energy
  As in Geant4 standard, but improved dE/dX parameterization below 2 MeV using tables with the experimental energy loss data from 1 keV to 2 MeV and parameterisation below 1 keV .
  

Final state

• Geant3
  d-ray energy sampled according to the knock-on electron cross section.
  Final state from energy-momentum conservation.
  Fluctuation on restricted energy loss as for e-/e+ ionisation.
  

• Geant4 standard
  Adapted from Geant3
  Track incident particle up to range=0.
  Optional: produce d-ray below cutoff near bondaries.
  Alternative: Photo Absorption Ionisation model.
  

• Geant4 low energy
  As in Geant4 standard.