PIXE / fluorescence with Electrons for Carbon (Z<7)

Hello,

I simulate PIXE / x-ray fluorescence induced by electrons and I cannot produce characteristic x-rays for Z < 7. If I change my setup to x-ray excitation I can excite Carbon and lower. So this must be a problem of the electron ionisation / interaction cross sections.
I use the Livermore models and set all cuts to 100eV. I tried all possible fluo, pixe and pixeElec options but could not find a solution.
I had LivermoreIonisationModel print out the cross sections and they look okay. Is there an internal or external production cut for electron PIXE somewhere? Or am I looking in the wrong files/ classes/ process options?

Thank you!

_Geant4 Version: geant4-11-00-patch-03 (16-September-2022)
_Operating System: Oracle Linux Server4 9.2
_Compiler/Version: gcc (GCC) 11.3.1 20221121
_CMake Version: 3.20.2