# Comparing manual integration and cumulative fluxes from USRBDX

Dear Fluka experts,

I am following up on an earlier post which I made:

I am trying to sum the differential neutron flux (integrated over solid angle) for neutrons with energies between 1.333e-11GeV and 1.317e-10GeV.

(Method 1) To do this when I I refer to the sum.lis file, I extract the cumulative flux in line 405 & 2nd cumulative flux column and subtract the value in line 402 & 2nd cumulative flux column.

(Method 2) If instead, I look at the values in the corresponding tab.lis file, I would naively sum the fluxes given in lines 4-9.

But the values obtained in Method 1 and Method 2 are different. Clearly I am not understanding something(s). If you can lead me in the right direction, I would greatly appreciate it! I’ve attached my output files for your reference.

Kind regards,
Dalini

Dear Dalini,

the method of calculating cumulative fluence between two energies using the .sum.lis file is correct.

However, when you are using the .tab.lis file, you need to keep in mind that the unit of the results are 1/GeV/cm^3/primary. So to calculate the cumulative fluence, you need to integrate, i.e. multiplying each value with the difference of the maximum and minimum energy of the relevant bin, then you can add them together.

This way, you will get the same results (beside some differences coming from numerical precision of the results)

Cheers,
David.

Dear David,

Thanks for your response. However, I proceeded with this calculation and found that the values were different by almost an entire order of magnitude.

Here is a screenshot (as I cannot attach my excel file) showing the integration from the tab.lis data (provided in original post).
-Col. C is Col. B - Col. A
-Col. E is Col. C*Col. D
-Col. G is the sum of values in Col. E in the range indicated by the red bracket on the left hand side.

-Col. H gives the cumulative fluxes at the appropriate energy bounds from the sum.lis file.
-Col. I is the difference between the cumulative fluxes.

As you can see, the values in Col. G and Col. I are different as I originally indicated.

Please let me know if you can tell what went wrong here. Thanks in advance.

Kind regards,
Dalini

Dear Dalini,

The sum in column G is clearly incorrect, as E3+E4 alone is greater than G3.
It looks like in your calculation G3=E3+E8, and not G3=SUM(E3:E8).

Cheers,
David

1 Like

Resolved! Thanks David.