# Maximum energy transferred to secondary electrons

_Geant4 Version:_11.1.1
_Operating System:_Ubuntu 22.04.3 LTS

I am simulating electrons in sub-keV regime impinging with microparticle. Now I met two questions with which I would like to ask for help:

1. Max. transfer energy to secondaries: I plot the energy transfered to secondaries by ionization. It demonstrates that only half of the primary electron energy could transfer to secondaries. Also I find the corresponding code as follows:
``````           fEnergyTransfered += energy;
if (energy<fEtransfMin) fEtransfMin = energy;
if (energy>fEtransfMax) fEtransfMax = energy;
``````

Why max Etrans is only half of incident energy?

1. In EMLivermore constructor, MSC method Goudsmit-Saunderson can be available: Emin= 0 eV Emax= 100 MeV Nbins=120 100 eV - 100 MeV. Although it sets Emin=0 eV, bin begins with 100 eV. Could I set cut range to 10 eV? If not, please explain the reason.

Hello,

In the case of identical particle (e- scattering on e-) one cannot distinguish final state and projectile, so max energy transfer should be 0.5E (E is primary energy). The same would be if proton is scattered off proton.

In the case of models per energy interval it is needed to understand that there are two different things: applicability interval of a model, emin and emax of the dEdx and cross section table. Applicability of models for Geant4 EM physics should be defined in a way that for each value of energy (even for zero) one and only one model should be defined. The tables for dEdx or cross section are pre-computed independently on model applicability. Because most of these tables have logarithmic scale they cannot start from energy zero. In EM physics they started from 1 keV (standard physics) and (10 or 100) eV for low-energy physics.

VI

Hi,

Thanks a lot. It makes more sence.