Tracking gamma production from Na22

Dear Fluka forum,

I trying to get to grips with using Fluka for simulations of gamma-ray generation from a Na22 source.

I have started with a toy model where I want to track the energy deposition and spectrum of gamma-rays emitted from a small cylindrical Na22 sample placed in a sphere of water. I believe I have set the source up correctly using:

BEAM               0             10000.0                              ISOTOPE
HI-PROPE          11        22
RADDECAY           2                             0
BEAMPOS            0         0         0         0         0
BEAMPOS            0       0.1         0       0.2                    CYLI-VOL

To track the energy deposition I used USRBIN:

USRBIN            10    PHOTON       -21        20        20        20DoseEqGrid
USRBIN           -20       -20       -20       500       500       500 &

and for the spectrum USRBDX:

USRBDX            -1    PHOTON       -22       WAT      VOID          EnSpec
USRBDX        100E-7      1E-7      3000                             1 &

However, currently written by the USRBIN or USRBDX routines which means flair fails to plot the results.

I can see a proportion of secondary photons are being created but am unsure why I can’t see then in USRBIN/USRBDX:

Number of secondaries generated in inelastic interactions per beam particle:
 Prompt radiation      Radioactive decays
   0.0000E+00 ( 0.0%)   1.0004E+00 (34.5%) PHOTON  

In addition when trying to plot the USRBIN the log shows this in the output - could this warning be part of the problem - I am unsure how to start troubleshooting the particle weight being reset.

   !!!! Something weird occurred: the total   !!!! 
   !!!! particle weight is reset to 1. Please !!!! 
   !!!! check carefully the input and the     !!!! 
   !!!! results                               !!!! 

I attached the .flair file here.
gamma_product.flair (1.7 KB)

Dear James,

your uploaded .flair file seems to be an earlier version of your simulation, missing the parts you mentioned in your post.

Could you upload the current version of the input file?


Dear Dávid,

Thank you for the reply, apologies, here is a more recent version.

gamma_product.flair (3.8 KB)

Dear James,

you don’t see any results in the USRBIN and USRBDX scoring because you are missing the DCYSCORE cards for these scorings.

Your source looks correct, however, I would set the energy on the BEAM card, for a few MeV higher than the highest energy line on the isotope.

Finally, I didn’t encounter the error about the reset of the particle weights with your input using the latest FLUKA release.


Dear Dávid,

Thanks so much for the help. Yes this explains why I couldn’t track them.

Adding the following card allowed me to track gamma photons:

DCYSCORE          -1                    DoseEqGrid                    USRBIN