Heavy ion Stopping Power at boundaries

Hi All,
Somehow I couldn’t get relevant posting to the issue I am having.
I have been trying to calculate the Si28 ion energy deposition in a Silicon medium
as a function of the stopping power. The Si28 ion is sourced in a sensitive volume
using a spectrum having maximum energy of 20 MeV. The sensitive volumes are cubes
1 nano meter and few nano meters on the side. When the Si28 ion
reaches the volume boundaries, the calculated stopping power in most
case is very large. In some case greater than 100 MeV-cm2/mg. I don’t think this is
expected for a spectrum with max 20 MeV energy. The tracking length is also given as a distance between the prestep point and the boundary point. I am just wondering if the energy deposition
I get from Geant4 is overestimated for the track length calculated. I tried to implement
recommended skin and geometry factors, but didn’t help. I greatly appreciate your
advice and help.

My impression is that the problem could be that you have a very small volume, it also depends on how you calculate the stopping power. A test I would suggest is to increase the lateral size of the sensitive volume (e.g. 1 micrometer, 100 micrometers). Look if you get the LET you expect. If you do not get it, maybe the problem is in the calculation of the LET. I hope this helps you.

Hi @guatelli!
Thank you for the response. My LET calculation is ok. But I have
been thinking about what you mentioned regarding the small volume.
Not sure what can be wrong when going to that small volume.

The models you are using are based on the condensed history approach and use multiple scattering theories. If the volume is too small (e.g. 1 nm linear size), the physics models start not to work as they should. Look for example at this paper: "Investigation of track structure and condensed history physics models " by Peter Lazarakis, Sebastien Incerti et al. . It explains the problem.

Hi @guatelli,
Thank you for the advice. I will implement soon.
Thanks for the reference as well.