I am trying to simulate the energy deposition of electrons and protons with different energies in the target material. When I was using electrons for simulation, I found that with the decrease of energy, the dose at the edge of the material was significantly lower than that in the middle, and there was a semicircular high dose area at the back of the material in Geometry, but the area of my source was larger than that of the target material.
The input is Round Glass.inp (3.2 KB)
My question is why the dose is mainly deposited in the back part of the material and shows this semicircular shape. I don’t know if I’m ignoring some physical process.
the dose profile seems to be realistic. There are a few phenomena involved in the energy distribution shape:
The energy deposition distribution for ~20 MeV electrons shows a global maximum at ~cm ranges. This explains why the maximum dose is in the back of the material.
From (Particle interactions with matter - CERN Document Server)
The semicircular shape arises from the fact that a fraction of the electrons escape from the lateral side of the target.
This happens because electrons strongly interact in the medium, changing direction stochastically each time an interaction occurs.
Therefore, the dose profile at the beginning of the target is uniform, because most of the electrons are still traveling parallel to the starting direction. However, after ~0.5/1 cm, a significant fraction of the ones which started on the edge of the target are deflected and enter the air region. Since the interactions there are much less probable, they continue their trajectory without reentering in the target.
Let me know if you have further doubts.
Cheers,
Daniele
