G3 to G4
Ionisation by e-/e+

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

• Geant3
  S(E,Z,Tcut): Moller (e-) or Bhabha (e+) formulae.
  dE/dX (E,Z,Tcut): Berger-Seltzer formula with Sternheimer density correction.
  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
  Subshell cross sections from EEDL data set.
  energy limits: 250 eV - 100 GeV
  

Final state

• Geant3
  Sample the d-ray energy from Moller or Bhabha differential cross section.
  Final state from energy-momentum conservation.
  Fluctuation on restricted energy loss from a L. Urban model.
  

• 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
  Sample the d-ray energy from parameterised formulae, where the coefficients are obtained from EEDL d-ray spectrum data fitting.
  Final state from energy-momentum conservation.
  Fluorescence from EADL transition probabilities.