Hi Lovepreet,
we can focus on a purely electromagnetic problem
Indeed, my comment above was triggered / in relation to this sentence in your original question:
(maybe related to the dependence of the cross sections on the energy of the particles, the reactions that take place, etc.)?
to indicate that nuclear reactions were not relevant in your problem.
Regarding electron interactions, in the reply to the aforementioned post I tried to elaborate how the basic interaction mechanisms at play manifest themselves in your problem.
For additional information, and to also have a first introduction to the relevant interaction mechanisms for photons, you may want to have a look at this (very gentle) overview presented in the last FLUKA Beginner Online training (click on the various days and the respective “clip” icons to access all material session by session).
Cheers to a nice weekend,
Cesc