Scoring residual particle fluences from activation

Hello FLUKA experts!

I asked this question during the last course (which was excellent by the way, thank you!) and am now at the point of trying to execute it.

I have successfully run a simulation of a beam on an apparatus and can get dose rate maps and isotope inventory at a given time after the beam is turned off for the activated materials. I would now like to look at the flux through some given volume from those decays, ideally looking at only certain energy emissions, say <100keV. Doing this by hand, I could take the isotope inventory and activity given by FLUKA, look up the spectral lines for each isotope, make some geometry assumptions and sum up the contributions. This would take thousands of individual calculations. It seems FLUKA already knows what isotopes are there, how much activity they have, where they are located and how they are decaying. Is there anything I can do to use FLUKA to take this even 1 step closer to the final answer? Essentially taking the output of an activation simulation and using it as an input for a flux simulation. I am ultimately looking for units of counts/cm2/s/keV

Thank you!
-Jason

Dear Jason,

To get the fluences in your activation simulation you can add USRTRACK or USRBDX scorings for ALL-PART (or PHOTON, ELECTRON, etc. separately) associated with DCYSCORE cards to get the residual particle fluences.

Essentially, FLUKA also uses the fluences to calculate the residual dose rate using conversion factors.

The results would be in [1/GeV/s] or [1/cm^2/GeV/s] depending on whether you provide the volume / surface area of the scorings.

Cheers,
David

Hi David @horvathd

I tried several iterations of USRBDX and USRTRACK with a small (1cm^3) detector volume right next to the material that is activated during the beam on target simulation. It looks like USRBDX is what I would want. In the output I can set up linear bins from 0-100 keV photons which is perfect but I keep getting zero counts in all of the bins. Since the detector is right next to the activated material and I even tried very short time for DYSCORE I find this difficult to trust. I also tried ALL-PART and PHOTON but still no luck. Any thoughts?

Thank you!
-Jason

Dear Jason,

could you share your Flair project file, so we can take a look?

Cheers,
David

Thanks you for taking a look! Activation_study_JO.flair (29.6 KB)

-Jason

Dear Jason,

The issue seems to be that the regions for the Reg and to Reg options on the USRBDX card are the same, but they should be two neighboring ones.

And a couple of remarks:

  1. The Detec region has AIR assigned to it, instead of VACUUM.

  2. The results of prompt DOSE-EQ scorings are not valid, since you apply a 33keV / 100 keV * 9999.9 = 330 MeV / 1 GeV transport cutoff to electrons and photons with the RADDECAY card. I would suggest to simulate the prompt radiation separately with the cards related to the activation disabled.

  3. For the activation simulations I also recommend to lower the production and transport thresholds of photons and electrons with EMF-CUT cards to 1 keV / 0.33 keV respectively.

  4. It is possible to score multiple decay times in one simulation, you only need to duplicate your scoring cards, give unique names (like: deq_t1), and assign the cooling times with multiple DCYSCORE cards.

Cheers,
David

Hi David,

Thanks so much for the tips, I have been playing with things and getting some results.

I changed the Reg and to Reg to “Air” and “Detec” respectively. I am assuming this means I am looking at photons going from the “Air” region into the “Detec” region. I added the rest of your remarks. There was a lower limit for EMF-CUT of 1e-6 for electrons so I settled for that. I also removed the prompt part of the problem as it is not pertinent for this project. I do have a little confusion in the units of the output. in the sum.lis file the units are shown as particles/GeV/cm^2/pr but it is listed as a flux so is this the same as particles/GeV/cm^2/s?

Thanks very much for your help! I did not think this was possible in FLUKA and am very happy with the outcome so far!

-Jason

Dear Jason,

  1. On your USRBDX card you selected a two-way fluence scoring option, marked with “\Phi{2}...”, which means fluence scored from the region Air to Detec and from Detec to Air as well. If you want a true one-way option, you need to choose “\Phi{1}...” instead.

  2. In the sum.lis files the printed units are unfortunately unchanged even, you are scoring activation. But the values should be per second instead of per primary.

Cheers,
David