We are studying low energy ( < 20 keV) electrons emission from flat samples. There is a problem with the momentum change at the point where an electron leaves the surface (process: Transportation).
The distributions of change between preStepPoint->GetMomentumDirection() and postStepPoint->GetMomentumDirection() is highly asymmetric along the y axis, (see the figure). While changes in x and z axis are approximately symmetric, the difference in y-direction is almost always negative. This behavior is independent of the emission energy. The surface is in the x-y plane.
The sample is a simple box, 1 mm big in every direction, position of the center is (-0.5, 0, 0). Electrons are being shot in direction perpendicular to its surface from the distance of 1 um (along the z axis). The box is either gold, silicon or carbon (the problem is with all of them) and is surrounded by vacuum.
What could be wrong?
Geant4 Version: 11.4.1
Operating System: Windows 11
Compiler/Version: Visual studio 2022
CMake Version: 4.3.0