Thank you very much for your kind help and patience! Disclaimer: I come from a different field of computational physics, so my apologies for the confusing explanations…
I do not understand the results. The track length depends on the physics processes that are happening and also on the physical sizes of the sensitive volume geometry.
I did not explain myself clearly: What I plotted was actually the spectra, ie particle flux vs energy. The particle flux was calculated by accumulating the track lengths of all secondaries inside the phantom. I calculated the spectrum for the whole phantom, instead of at some small volume at a given depth.
plot the edep due to the neutron field in the water cylinder with respect to depth. You can distinguish secondary particle types and their contribution to edep. Check if the results are what you expect.
I actually had already verified that depth curves (edep, kerma and particle fluence) match the results obtained with MCNP. So in principle I am confident that the simulation “works”.
Plot the energy spectra of the secondary particles of interest at different depths in the water phantom. Again, are the results expected?
Ah, I actually found a reference for the photon spectrum at 2.5 cm depth, and it has similar features to my “total” spectrum. The spectrum is in linear coordinates though, so the discontinuities I am talking about would be impossible to observe.
I hope this clarified a bit what I am doing? I’ll try to rephrase: I am observing some discontinuities in the photon and electron spectra at low energies, and I don’t know if it’s a mistake I made or a feature