Uncertainties in USRBIN

Hello everybody,

I am trying to score the dose that is deposited by an electron beam in a certain region. However, using USRBIN, both when I score over a region, and when using a cartesian mesh, I get uncertainties of 100%. That still prevails when I use a lot more primary particles (I have tested it with 5000, 20000, 50000 primary particles). I also went on to score over 10 instead of 5 cycles. I also put Still, 100% uncertainty all the time.

I also tried to do the tutorial provided by CERN, and even follwoing that step by step guide I get uncertainties of more than 100%.

How can I get those uncertanities down?


Dear Tasha,
can you please provide your Flair project *.flair file demonstraiting this issue.
Can you please describe where you check the uncertainty percentage?

Kind regrads,

Hi Illia,

here is my .flair file:

WaterProjectSEALAB.flair (14.8 KB)

I score quite a lot things there, mostly to check and double check what is going on. The problem persits in all of those scorings tho. The uncertainty I got from the geometry tab, where when clicking on “info” it gave me the scored results per bin, plus minus in the uncertainty in percent.
However, I just saw that when I use the bnn → ascii option in the Run - Files tab, the table giving erros consistantly only show 0%, which also sounds wrong.

Hope you can help me with this!
Thank you and best regards,

I realised, that when I go down to only ~1000 primary particles, in the .bnn.lis file, I do get a statistical error which is not zero.

If I go higher with the amount of partciles, the uncertainty will go down to 0.

For both cases, in the geometry tab, I still see the ± 100%.

I do scale the values in the layers section of the geometry tab. So maybe, the uncertainties do not get scaled? Or maybe just the 0% uncertainty in the .bnn file gives an error in the geometry tab?

Yeah, so I just saw that. Maybe that helps with anything.
Thank you again. Cheers,

Hi @TashaSpohr

I can’t find in your file the AUXSCORE (Fluence-to-dose conversion coefficients) AMB74 card and the PHYSICS packages cards, If I’m not mistaken you should active them, please check slides 12 and 32 here.

For the sake of clarity: the scoring of absorbed dose (Gy), obtained as DOSE in GeV/g from FLUKA, has nothing to do with fluence-to-dose conversion coefficients.
These are instead required for the calculation of dose equivalent (Sv), obtained as DOSE-EQ in pSv from FLUKA. Nevertheless, the AMB74 set of conversion coefficients is used by default with no need for the AUXSCORE card (see the manual).
Also, no specific PHYSICS card is necessary for electron beams of the considered energy.

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Dear Tasha,
I can confirm, that that uncertainty value for the dose calculation is indicated as about 100 when the USRBIN scoring results are plotted in the geometry tab. This is also in my models, you may share one of your models to compare, and probably @ceruttif may comment on that. However, your approach with bnn → ascii option in the Run - Files tab, gives meaningfull values.
I will try another Flair distribution on Monday, to be sure that it is not installation specific difference.

Kind regards,

Dear Tasha,

it seams from my short investigation, that the problem is rather *.flair file version-specific problem.

The input file looks slightly different when I open your .flair file in different versions and installations of Flukla. Coping the input into a new Flair project helps to obtain meaningful data for “bnn → ascii option”. However, the Geometry tab USRBIN layer issue remains for your .flair file for both Flair versions I have.

I suppose, that your .flair file was edited outside the Flair environment, or damaged by several resaving in various Fluka versions (some empty REG1 appears in Ubuntu Flair 3.2 version, and does not in a newer MacOS version, etc.).

I suggest transferring your project to the new one line-by-line. Also, I suggest avoiding the output of both binary and ascii results into the same file (like 50 BIN and 50 ASC). Such minor changes to your file helped in my case.

Let me know if it helps in yours.

Kind regards,