I am using a histogram energy spectrum input to gps in a macro file and I am scoring the energy spectrum 0.1cm from the source to check that the spectrum output matches the input. However, I find that G4 matches the mean energy well but underestimates the lower energy regions by up-to maybe 5%. I am trying to do detailed dosimetry calculations and it is vital I reproduce the energy spectrum exactly. Does anyone have any experience with this? This commands in the macro file are shown below:
/gps/ene/type Arb /gps/hist/file hist_input.txt /gps/hist/inter Exp
The input energy spectrum I am using comes from a EGSnrc simulation for a particular real life accelerator and has been thoroughly documented so I am sure that there are no issues with the energy spectrum. I also find that G4 essentially shifts the whole energy spectrum up by half a bin width, so I have to reduce the energy value in the hist file by half a bin width so that it matches the input spectrum from EGS. Here is the plot of the input and output spectra. EGSnrcSpectrum_G4RecreatedSpectrum_Comparison.pdf (14.9 KB)
Thanks for reading and for any help!