Proton dose in water

Hello all,

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,


Could you be more specific? Is the incident energy, position and direction of the proton always the same?
Is the proton only propagating through water or first through some materials before reaching the water?
I would actually expect several peaks if the proton propagates through different materials…it will lose energy there before reaching the water volume.