I first used a large area proton detector (5x5 cm^2) for depth dose measurement and got the following results:
But when I shrunk the cross sectional area of the detector to 5x5 mm^2 the result appeared as this:
I used a 150MeV proton beam irradiating directly into the detector in water. Could there be a physical explanation for the discrepancy in the results? (I personally thought that the protons might exit the thin detector as they pass through it due to their transverse straggling, could that be a correct explanation?) Or there should be something wrong with my code or with the detector?