Include Transportation Processes in Total Energy Deposition?


I think I understand from previous posts on this forum that the “transportation process” in Geant4 is not a physics-based process like ionization or the photoelectric effect. If I understand correctly, it is a type of administrative/programmatic process used by Geant4 to handle particle transport across volume boundaries (among other things).

However, in my post-analysis of my Geant4 simulations, I see that the transportation process can have nonzero energy deposition associated with it. If I’m interested in calculating the total energy deposited within a sensitive material in Geant4, should I exclude step points that are associated with transportation processes? That is, should I calculate the total energy deposited within the detector using only physics-based processes and exclude any energy depositions associated with transportation processes?

I believe that the answer would be yes based on a previous post, but I wanted to confirm.

Transportation itself should never have an energy deposit. It is strictly about moving the particle from pre-step to post-step point (and setting the post-step point in the case of hitting a volume boundary). For charged particles, there are AlongStep processes (G4VContinuousProcess) like multiple scattering and ionization which produce energy deposits (dE/dx) along the length of the step.

Those along-step processes are not step-limiting. They are invoked for all steps, and will never show up as the “process which limited the step.” If you see Transportation as the “process which limited the step,” that means you hit a boundary. You should still collect the energy deposit (dE/dx) for those steps.

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Ah, I see. Yes, I believe that I’m seeing nonzero energy deposition for steps where Transportation is the process that limited the step. I had thought that I may be “double counting” energy depositions if I included these steps in the total energy deposition. Thank you for your explanation.

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