14 MeV protons through 12 mm air: segmented energy spectrum obtained

Dear FLUKA experts,

I’m propagating 14 MeV protons (pencil beam) through 12 mm of air and scoring BEAMPART vs. (I1,LinE,LinOmega) to obtain the energy spectrum. I get a segmented spectrum, as you can see in the figure. I tried changing FLUKAFIX and PART-THRES in several ways, but the result did not change. I also noticed that the spectrum becomes smooth if the starting energy is 10 MeV or less instead of 14 MeV. Can you please help me? Thank you in advance.

Kind regards,


spettro prot bassaE attraverso materiali.inp (1.6 KB)
spettro prot bassaE attraverso materiali.flair (3.8 KB)

Dear Enrico,
as you will immediately realize, the reason of your problem is actually pretty coarse.

In fact, Flair is plotting the content of the (human-readable) _tab.lis file, which is generated via the Run/Data frame by the Process button, invoking (in the USRBDX case) the usxsuw utility. The number of digits of the energy value in the aforementioned file (4) is made insufficient by the extremely small energy bin width you requested (0.4 keV, to be compared to 14 MeV energy values), hence the resulting plot anomaly, which is unrelated to your FLUKA run.

Go to the src/tools directory of your FLUKA installation, open the usxsuw.f file, search for the

 9501 FORMAT (4(1P,1X,E10.3))

instruction, change E10.3 to E12.5, save the file, go to the src directory and type make.
This will produce (in the bin directory) a new version of the usxsuw utility, generating via Flair a _tab.lis file with two more digits in the printed values, and ultimately a smooth spectrum.

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Dear Francesco,

thank you for your kind explanation and instructions. At home now, I will try that tomorrow once back to my work PC. Just to be super safe: are the instructions good even if I’m running FLUKA in a Windows Subsystem for Linux?


yes, to be performed on the Linux terminal. All right?

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OK Francesco, thank you again.