TABLE II.

Geant4 physics models to describe EM physics processes in Geant4 EM constructors under investigation.

Geant4	Opt0	Opt3	Opt4	Livermore	Penelope
Rayleigh scattering and photoelectric effect	Livermore				PENELOPE
Compton scattering	Standard	G4KleinNishinaModel	G4LowEPComptonModel for E < 20 MeV* Brown et al 2014 [36]	Livermore for E <1 GeV*	PENELOPE for E < 1 GeV*
Gamma conversion	Standard	Standard	PENELOPE for E < 20 MeV Standard for E > 20 MeV	G4BetheHeitler,5DModel for E < 1 GeV, Standard for E > 1 GeV Bernard et al 2013 [37]	PENELOPE for E< 1 GeV, Standard for E > 1 GeV
e− and e+ ionisation	Standard	Standard	Livermore for e− for E < 100 keV, PENELOPE for e+ for E < 100 keV, Standard for E > 100 keV	Livermore for E < 100 keV Standard for E > 100 keV	PENELOPE
e− and e+ bremsstrahlung	Standard	G4SeltzerBergerModel for E < 1 GeV, G4eBremsstrahlungRelModel for E > 1 GeV			PENELOPE
e+ annihilation	Standard				PENELOPE
e− and e+ multiple scattering	Urban model for E < 100 MeV (Ivanchenko et al 2010 [39]), Wentzel model for E > 100 MeV	Urban model	Goudsmit-Saunderson model (Incerti et al 2018a [38]) for E < 100 MeV Wentzel model for E > 100 MeV
Coulomb scattering	on	off	on
Bremsstrahlung angular distribution	ModifiedTsai	2BS			PENELOPE

^*:G4KleinNishinaModel for higher energies. Geant4 10.5 is considered. For details on the models the reader should refer to the Geant4 Physics Reference Manual [28].