Low energy electron beam through material

Hello All,

I created a simulation of an electron beam through an extremely thin diamond. I am interested in the excitation of electrons in the Bethe-Bloch region. For energies > 500 keV it seems that the ionization (calculated via the Bethe formula) and Bremsstrahlung radiation are dominant. For energies < 500 keV the energy deposit is governed completely by MSC as the output reports, which does not appear at energies>500keV. Is it safe to interpret that these scatters are nucleon scatters, and that these low energy electrons are no longer in the Bethe-Bloch region, and so electron in the material are no longer largely becoming excited? Or is the effect still in place but the nucleon scatters are dominating with respect to step size through the detector and so I am only getting a portion of the reporting of processes?


you misunderstand tracking information. Energy deposition always determined by ionisation process at these energies. Multiple scattering defines only step size.



I am trying to simulate the secondary electron emission (SEE) spectrum and the secondary electron yield (SEY) for a few tens of nanometers thick metals.

I started from the TestEm5 example which is the most relevant and tried to get the SEE spectrum with a monoenergetic electron beam (world is vaccuum in that case)
and compare it with some measurements that already exist (for e.g. for Cu or Stainless Steel: https://www.slac.stanford.edu/pubs/slacpubs/9750/slac-pub-9912.pdf ).

In the TestEm5 example the SEE spectrum can be already obtained from the existing histogram number 30 ("(reflect , charged) : kinetic energy at exit") by normalizing
it (1 over the Integral) I think. What it confuses me is the spectrum of the true secondary electrons (<50 eV) which are affected by the lower production cut (/cuts/setLowEdge)
and the range cut (/run/setCut or /run/setCutForAGivenParticle). I thought that the production cut should be set at least equal to the work function of the metal
(+some kinetic energy needed for the electrons to escape from the metal). Having that threshold fixed I started to scan on several range cut values by counting
the number of secondary electrons produced to find the best threshold. And once these are fixed to go ahead and see the effect of the lowest electron limit
(/process/em/lowestElectronEnergy) and the stepMax. I forgot to mention also that the best SEE spectrum close to the reference data I got it by using the
Livermoore (or emstandard_opt4; seems to be the same on these very low eV ranges). Using this LP-cut I already have a cut on the corresponding histogram and
the distribution of the true secondaries are shifted wrt to the reference data. But setting it very low (for e.g. 10e-5 eV) I start to get distributions more close to the reference data (not exactly but more close) and these started to confuse me.

Sorry for my very long post but after having spend a couple of weeks scanning these thresholds and making correlations between them to understand what is happening
I only got more confused. I also saw the DNA example but I read it is optimized only for water and the one for the microelectronics it says that it is only valid for
Silicon. Is it maybe a problem that below 10eV there is no good accuracy of the Livermoore model as I have read in the geant4 webpage?

Or I should continue on trying to find the optimum set of these cuts?

Thank you in advance,

p.s. I have attached a plot where the LP_cut is equal to the work function of the stainless steel.
Stainless_steel.pdf (29.1 KB)