0.9 keV cutoff on Gamma spectrum with G4MuBremsstrahlungModel!

Physics Processes, Models and Cross Sections
1

Hello Geant4 experts,

I extracted the kinetic energy spectrum of the gammas produced from bremsstrahlung for muons with energy 10^5 MeV. I found that no gamma below ~ 1 keV is produced, the spectrum suddenly drops to zero below 1 keV. As I looked at the G4MuBremsstrahlungModel.cc code I saw a hard-coded minimum threshold being applied at 1 keV (minThreshold(1.0*keV)). I am wondering if this could be the reason for this sudden drop in the energy spectrum and if the spectrum can be extended to a smaller energy range as well.

My simulation details are as follows.

  1. Geometry : A cylindrical germanium detector; thickness : 2.5 cm , diameter : 7.6 cm
    Particles are shot normally downwards on the top surface.
  2. Incident particle: muons, energy: 10^5 MeV; processes: for incident muons all processes except bremsstrahlung are switched off.

I would appreciate any help you can provide in this regard.

Thanks and regards,
Samir Banik

2

Hello,

your analysis is correct. The reason was to avoid numerical problem. For high energy muons the low-energy part of bremsstrahlung gamma have high cross section and low range. Note that production threshold 1 keV is very low.

VI

3

Hello,

Thank you so much for the reply. About this model I have couple more questions. I would appreciate if you can help me understand those as well.

  1. Does the G4MuBremsstrahlungModel (like electron bremsstrahlung models as described in Physics Reference Manual) take care of Landau Pomeranchuk Migdal (LPM) and dielectric suppression?
  2. Can the minimum threshold be extended at least till 100 eV? I am interested in the low energy region for my study.

Thanks and regards,
Samir Banik

4

Hello,

no for both. An extra investigation is required for the minimum threshold, we now cannot answer properly.

VI