Iodine isotope source

Hello FLUKA experts,
I’m new to FLUKA and I’m trying to simulate a radioiodine therapy chamber to verify the effectiveness of shielding. However, I encountered some issues with dose calculation and plotting. I’m not sure if the USRBIN card is correctly written or not. If you have any comments or suggestions, please feel free to help me.
Thank you!
room.flair (4.2 KB)
room.inp (2.9 KB)

Dear Hayat,
the USRBIN card is set correctly and you can use it with the plotting approach you have implemented, if proper normalisation factors will be used (please see for details, my only suggestion that you should use higher resolution (NX, NY, NY numers in the range of several hundreds) to have meaningful output.

However, please pay attention, that you have major geometry errors in your project (please set actual void1-2 and shielding dimension and position).
Also, you have partially implemented activation evaluation (with relevant physics), which probably is not really necessary for 6MeV electrons source (please review), and partially implemented various scoring cards and plotting.

Please set actual geometry of your setup, and ask for additional assistence for physics setting if it is relevant for you and you still face issues with your model.

Kind regards,

Hi fluka experts,
I’m attempting to simulate a radioactive source of iodine-131 emitting beta and gamma radiation. Could you assist me in selecting the appropriate physics settings?
Desintegration β-
Emax = 606 keV (89 %)
Emax = 333 keV (7 %)
Emission γ
E = 364 keV (81 %)
E = 637 keV (7 %)
E = 284 keV (6 %)

Dear Hayat,

I may suggest two ways to evaluate effects of Iodine-131 radiation in FLUKA.

1 - Using of separate user-defined radiation sources according to a list (as you propose in your post) for each energy and particle tape if it is convenient for a user or specific emission range (peak) have to be isolated.

In this case, you may use multiple sources (beams) in your model using SPECSOURCE and SPOTBEAM cards. For details see, Multiple beam spots section.

2 – A more elegant (for my opinion) and general way, is to use FLUKA built-in features to define the radiation source (beam type) as a radioactive isotope. Also, this method is partially implemented in your initial Flair file. In this case, beam particles should be set as ISOTOPE in the BEAM card, isotope decay should be set with RADDECAY card and HI-PROPE card should be used to set A/Z values for the isotope. Beam position can be defined as volumetric (card BEAMPOS, e.g. CYLI-VOL). Then, the radiation spectrum will be generated using FLUKA functions by itself.

In most cases for the Iodine-131 isotope decay you can start with the default physics setup (transport and thresholds) due to the emission energy range. Please find more details on radioactivity simulations using FLUKA in the course material, the isotope source definition is given on page 23 The source material should be set to iodine in the relevant region of the geometry to estimate self-shielding effects for volumtric sources.

Kind regards,


Thank you very much for your help.
I’ve done all that you suggested. Now, I want to see the dose calculation results, but I’m not sure why the plot card isn’t working.
blindage.flair (3.2 KB)
blindage.inp (2.9 KB)

Dear Hayat,
the main issue you have is that USRBIN card in your model is set to score per region value, while plotting is an instrument for dose map/fluence visualization. Please set USRBIN type to XYZ and test visualization value, similar as we discussed before. Also, pay attention that source position and iodine sphere position are different in your model. Also, card IRRPROFI and PHYSICS are not needed for the described model.

Please let me know how do you proceed, and if additional help is needed.


What exactly is wrong with the position of my definition source?

@illia.zymak has already told you what the problem is: