Comparing USRBDX result with USRBIN result

Dear FLUKA experts,

I saw a similar topic posted here,
USRBDX detector area and fluence comparison to that by USRBIN:
but I still have more questions.

I ran a low energy neutron production simulation with a simple geometry. I invoked two scoring cards - USRBDX and USRBIN. In my geometry, I included a detector box of total surface area, 6cm^2.

The USRBIN scoring card tracks the neutron fluence in a volume of space which exactly covers the volume defined by the detector box.

The USRBDX card scores the one-way differential fluence (no. of solid angle bins equals 1) of neutrons from the region defined by the box to the volume of space outside of it.

I plotted a 2D map of the fluence in Flair. Flair gives me an integrated value. I compared this value with that of the cumulative flux provided at the top of the sum.lis file provided by USRBDX.

Integrated value obtained from USRBIN in Flair: 5.98E-005

Result from USRBDX (without area normalization): 8.7109998E-05 +/- 1.612777
Result from USRBDX (with area normalization): 1.4516667E-05 +/- 1.612777

These values are different, but I know that USRBIN and USRBDX should gave the same result, within statistical uncertainty. Please let me know what might be wrong in my analysis.

Thank you for your guidance.

Kind regards,

Dear Dalini,

Could you please provide your flair file to better understand the issue?


Hi Marta,

Thanks for your reply. Please see my input file attached.

For the USRBDX card, I am scoring the one-way neutron flux flowing from region “Det” to “Mod”. For the USRBIN card, I am scoring the neutron fluence over the volume of space spanned by the region “Det”.

Thanks in advance for looking into this!

10MeV_Be_1pt5cmProt_r8_t10_thermsurv.inp (2.9 KB)

Dear Dalini,

First of all, sorry for the very late reply.

What I see in your input is that the USRBDX you define is “current” and not “fluence”. The latter is the quantity you need to score in order to compare the two types of scoring results. In addition, the two-way scoring should be selected instead on one-way to make them compatible.
Like this, both quantities should match within uncertainties.

I hope this helps you to better understand the issue.


Dear Marta,

Thank you for your reply. I was on vacation when you posted this, hence my late reply. I will do what you said and see if these quantities turn out to be comparable.

Kind regards,