[Simulation question]: g4em-dna_opt2 vs. g4em-standard_opt4 (dose point kernel for monoenergetic electrons and photons)

[claus-e-andersen]

Simulation question

I have performed dose-point kernel computations in water for mono-energic electrons and photons. I have worked with a point source and a set of concentric spheres placed inside each other (see script for details). I have both used g4em-dna-opt2 and g4em-standard_opt4.

For photons, I see good agreement between the two physics lists. For electrons, however, I see significant deviations in the "bremsstrahlung tails". Below are the examples for 10 keV, 100 keV and 200 kV particle energy at distances from 1 um to 3 mm from the point source.

The main deviations for the electrons are beyond the CSDA range for electrons (indicated in the graphs by a vertical dashed line). My interpretation is that the two physics differ with respect to bremsstrahlung PRODUCTION rather that with respect to the TRANSPORT of photons.

I have three questions:
(a) Which of the two lists give the "correct" results for electrons at "large" distances (i.e. when only the bremsstrahlung is left)
and (b) do I need to set the cut-off parameters etc:. differently for the two physics lists ? (see below) (c) Perhaps I need to set some other parameters differently to get the bremsstrahlung production "right"?

Many thanks for any assistance with this problem.
I have attached a sample script and the results.
With best regards
Claus

Claus E. Andersen, DTU Health Tech, Denmark

Here are my main settings:
###############################################################

Physics

###############################################################
s:Ph/Default/Type = "Geant4_Modular"

Select either g4em-dna:

sv:Ph/Default/Modules = 2 "g4em-dna_opt2" "g4radioactivedecay"

OR g4em-standard:

#sv:Ph/Default/Modules = 2 "g4em-standard_opt4" "g4radioactivedecay"

d:Ph/Default/SetProductionCutLowerEdge = 250 eV
d:Ph/Default/EMRangeMin = 10. eV # minimum for EM tables
d:Ph/Default/EMRangeMax = 500. MeV # maximum for EM tables
#####i:Ph/Default/EMBins = 77 # number of bins for EM tables
i:Ph/Default/EMBinsPerDecade = 7 # number of bins per decade for EM tables
b:Ph/Default/Fluorescence = "True"
b:Ph/Default/Auger = "True"
b:Ph/Default/AugerCascade = "True"
b:Ph/Default/PIXE = "True"
b:Ph/Default/DeexcitationIgnoreCut = "True"
d:Ph/Default/CutForAllParticles = 1 nm

dpk-10030-photons-and-electrons.pdf
dpk-spheres-10067-simplified.txt

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[JoseRamosMendez]

Hi Claus,
Besides the intrinsic difference in electron transport between condensed-history (g4em-standard_opt4) and track-structure (g4em-dna_opt2), the g4em-dna-opt2 has not the bremsstrahlung process implemented. One option would be to create a customized physics list based on G4EmDNAPhysics_option2, and add to it the brem process.

For example, the TOPAS-nBio/processes/TsEmStandardPhysics_option4.cc (Topas module called "Tsem-standard_opt4") is defined the same as g4em-standard_opt4, with just an extra option to change the brem angular distribution. You could make something similar for g4em-dna-opt2 to add the brem process and rebuild Topas-nbio.
Best.

[claus-e-andersen]

Dear José
Many thanks for this clarification. It is (now!) very obvious that there is simple zero bremsstrahlung production for the g4em-dna_opt2 runs. - Claus