Difference in measured spectrum

Dear experts
I used a histogram sampling using source_newgen.f but when I am scoring the fluence spectrum using USRBDX and normalizing it for MeV and area, I am not getting the fluence (Y-axis) as that of input one.
Please help me to find the reason for the discrepancy, I think I am missing some concepts here.


Here are all inputs:
dummy.inp (1.6 KB)
dummy.txt (1.2 KB)
source_newgen.f (19.2 KB)

Dear Rohit,

FLUKA doesn’t take into account the absolute intensity of your source histogram/spectrum. The integral value of the histogram is automatically normalized to 1.0. You will need to multiply the results with the original intensity as it must be done with a simple BEAM source.

In your case, if I integrate your histogram, I get 0.000467 electrons per decay. After applying this normalization factor to the FLUKA result, I get back the input spectrum correctly.


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Dear @horvathd,

I got the point, thanks for your detailed explanation.