How to distinguish the reaction channel for low energy neutron irradiation

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Description

Dear FLUKA experts,

I have successfully scored PKA (Primary Knock-on Atoms) from neutron-induced recoils with mgdraw.f.
Now I need to go one step further and tag the reaction channel that produced each secondary particle (or residual nucleus) under low-energy neutron irradiation (En < 20 MeV).
The channels of interest are the standard ones shown below (taken from the ENDF MT hierarchy):

Reaction MT ENDF name Typical secondaries
elastic 2 n,n recoil ion, γ (Doppler)
inelastic 51–90 n,n' scattered n + excited nucleus → γ + recoil
radiative capture 102 n,γ γ cascade, recoil (A+1,Z)
(n,α) 107 n,α α + residual
(n,p) 103 n,p proton + residual
(n,d) 105 n,d deuteron + residual

My questions are:

  1. Which INCLUDE files and STACK variables inside mgdraw.f give access to the MT number (or any FLUKA-internal code that uniquely maps to MT) for low-energy neutron interactions?
    I already use INCLUDE (TRACKR) and INCLUDE (DTCFIL) for heavy-ion transport, but these seem to contain only the high-energy generator information.
    For En < 20 MeV the neutrons are processed by the group-wise or point-wise ENDF library, and I cannot find where the MT is stored.

  2. How do I distinguish the reaction channel in the following routines?

    • USDRAW (entry after each interaction)
    • MGDRAW (step-wise)
    • ENDRAW (energy deposition)

    so I need both the MT tag and the identity/energy of the recoiling nucleus.

  3. If the MT number is not directly accessible, is there an official user routine (or a FLUKA common block) that returns the ENDF reaction code or the residual nucleus (A,Z) after the interaction?
    I am happy to parse the residual and infer the channel myself, but I need to know where FLUKA stores it.

Any minimal working snippet (Fortran) or a pointer to the relevant INCLUDE file would be greatly appreciated.

Thank you in advance for your help!

Best regards,

2

This was just discussed and answered three weeks ago.
Moreover, you are actually not using the latest FLUKA release by CERN, which is 4-5.1 and does not contain any (DTCFIL) file to INCLUDE.

1 Like
3

Dear Francesco Cerutti,

I recently compiled a custom FLUKA (Latest Version) executable with my user routines and tried running it through FLAIR, but the simulation stops immediately with error code 12 and no output files generated. The build was successful, but the execution fails before completing the first cycle.

Here is my FLAIR output:

Screenshot From 2025-10-17 08-26-17
Screenshot From 2025-10-17 08-26-171920×954 128 KB
What I did:

  • Compiled successfully:

    • Source_NewGen.f (custom source routine)

    • mgdraw_empty.f (no modifications)

  • The executable nuclear_Channel was built successfully.

  • Input file: pka.inp

  • Run via FLAIR GUI.

Question:

  1. What does Error code 12 indicate exactly in this case?

  2. Does it mean there is a problem inside my Source_NewGen.f routine (perhaps invalid source coordinates or energy initialization)?

  3. Are there specific runtime logs or flags I can enable to see where the crash occurs?

    Source_NewGen.f (20.9 KB)

    pka.inp (1.8 KB)

    mgdraw_empty.f (11.7 KB)

4

Hallo, forget about error code 12 and read the content of the file /home/zeenat/Downloads/FLUKA/PKA/zeenat/fluka_62438/pka001.log.

5

Dear Expert,

Thank you for your guidance. I checked the directory you mentioned:
/home/zeenat/Downloads/FLUKA/PKA/zeenat/fluka_62438/

However, there is no file named pka001.log or any other log file in that folder. The directory only contains this files that shown in the figure below and the core file is empty.

figure
figure1529×479 41.9 KB