DETECT Card - Spikes in the Spectrum

Dear FLUKA Experts,
I’m running a simulation to measure the energy deposition in a low pressure (low density) gas (Tissue equivalent-Propane based).

I’m using a 62 MeV proton (point source) and scoring the deposition events via the DETECT card.
However, the obtained spectrum presents with some spikes as shown in the figure.

First thought it was a binning problem, so I changed to from the default 1024 to 2000 bins and still got the same results.
Then I added EMFCUT, EMFFUX, and PART=THRES cards with the settings shown and still got the spikes.

Please is there a way to get rid of these spikes? Is there something I’m doing wrong, otherwise is there any physical explanation to this?

Also what is the minimum threshold energy for electron production and transport in FLUKA?

Kindly advise.
DETECT_Card.flair (4.9 KB)
DETECT_Card.inp (3.2 KB)

Zavier N.

Hello Zavier,

Starting from the end, minimum thresholds for production and transport in FLUKA are 1 KeV for electron/positrons and 100 eV for photons.

The spikes are indeed wrong. My guessing is that the protons, travel through the target region in just one step, and the spikes you see are the result of that.
You correctly requested the EMFCUT card, but you activated it only for the transport of electrons. You should also add the production cut. To have the best precision, I would suggest to put the both thresholds at the minimal value.

Also, you need to set the DELTARAY card accordingly, selecting the same threshold energy for electron production. This is the most important card, since it also set a shorter step size for protons.

The PART-THRES card you used to reduce the threshold for proton energy down to 1E-14 GeV does not make really sense and it is not useful.

EMFCUT         -1E-6      1E-7             BLKBODY  @LASTREG
EMFCUT        -1E-06      1E-7      1E-5  BLCKHOLE  @LASTMAT          PROD-CUT
DELTARAY        1E-6                      BLCKHOLE  @LASTMAT
*Sets the size of electron steps corresponding to a fixed fraction of the total energy.
EMFFIX      Tissue-E     0.001     A-150     0.005  POLYSTYR     0.005PRINT

You can obtain similar results if you manually require shorter step size for protons. I would not encourage this procedure, since we are at the limit of the code: as condensed history monte carlo code, FLUKA is not able to simulate very short step sizes in diluted gasses. I attach here the related card

FLUKAFIX       0.001                      Tissue-E

Finally, despite not being stricly necessary here, I suggest you to switch on single scattering (MULSOPT card) when traveling in thin layers.

With those changes, I was able to obtain a more realistic spectrum. Let me know if you have any other questions.



Dear Daniele,
Thank you very much for your reply.
I see that you implemented both my settings (OLD) and your corrections (New) in the same input file of your first reply. May I ask how you proceeded to run this?
I tried to run and got this error (image 1)

Also, I was able to solve my problem alternatively, by just adding the MULSOPT card while maintaining all other settings and switching on single scattering as shown.

I see that you’ve also recommended it in your second reply but can I please get that input file?

Lastly, Is there an alternative way to arrive at the same results (i.e. energy deposition) without the DETECT card? Please advise.

Best regards

  1. The error you see is not related to the inputfile. In my simulation, I tend to use tsp (task spooler) to run cycles in parallel and test multiple options with less time. See this discussion for instance: How to use the maximum speed and memory available on your PC? - #4 by illia.zymak

  2. Very good! It is indeed a good practice to use single scattering when you have thin layers

  3. I attach here the inputfile:
    DETECT_Card.inp (3.9 KB)

  4. The DETECT card scores energy deposition on an event by event basis. This scoring option is indeed quite peculiar and is typically requested in detectors. You have plenty of options to score energy deposition, as USRBIN for scoring the (total) energy deposition on a regular spatial structure, or EVENTBIN which prints the energy deposition after each event.