I simulated a proton beam passing through some components and degrading in energy, and finally incident onto a water phantom. I collected all the proton hits and obtained the energy deposit profile inside the water as a function of depth in water.
I expected to observe a pristine bragg peak, however I see erroneous fluctuations at the tail of the profile as you could see in the figure below.
I would appreciate any hints to what may cause this problem?
Thank you so much,