Contributions to NIEL?

Advanced Features and User Routines
1

Dear Experts,

I am scoring NIEL-DEP (238) in silicon. Is it possible to extract the contributions to NIEL from the different particles or processes? Can I use user routine mgdraw.f to do this?

Thanks, Ian

3

Dear Ian,

Please find in the attachment an input file with a working example, where you can find the cards implementing the breakdown of NIEL in different particle types via an AUXSCORE placed after USRBIN. There is no need to use mgdraw.f.
The .flair file includes pre-configured runs and plots for the following setups:

  • No ion transport (run1)
  • Ion transport switched on via the IONTRANS and PART-THRES cards (run2) - note that PART-THRES is written only for ALPHAS, but this applies to all heavy ions. Also, the actual value of the threshold can play a role
  • Ion transport switched on, elastic reactions switched off
  • Ion transport switched on, inelastic reaction switched off

The comparison between run1 and run2 is particularly relevant, as in run2 you see a large contribution from heavy ions to the NIEL, which is not there when ions are not transported (run1). Physically, this is because recoil nuclei are in fact the sole source of NIEL (in the same way as electrons are the source of energy loss via ionization), but in run1 FLUKA assigns the NIEL to the incoming protons and neutrons because the ion transport is switched off, and also in run2 a contribution from neutrons and protons remains because of the non-zero transport threshold of ions. This means that care must be taken when assigning the NIEL to a given particle type, because the transport thresholds of ions are playing a major role in the simulations.

Instead, the last two runs are made to verify if the NIEL is dominated by elastic or inelastic reactions. As you can see, when removing the elastic ones the difference is minimal, while when removing the inelastic ones you get a large difference. This demonstrates that inelastic reactions are the dominant source of NIEL for the case under test (protons with 1 GeV momentum, i.e., Ekin~430 MeV, on a copper target).

I hope this clarifies the issue!

Giuseppe

nieldep.inp (2.0 KB)
nieldep.flair (8.3 KB)

4

Thank you Giuseppe, much appreciated!