Activation in thin stacked foils

Scoring
1

Dear FLUKA experts,

I am simulating a stacked foil geometry composed of alternating titanium (Ti) and zirconium (Zr) layers:

Ti – Zr – Ti – Zr – Ti – Zr – Ti – Zr

Each foil is 10 µm thick.

The stack is irradiated by an alpha beam with:

  • Energy: 17.5 MeV

  • Beam profile: rectangular, 1 cm × 1 cm

My objective is to calculate the induced activation in each individual foil.

However, the results appear questionable. In particular, for the Zr foils, I observe significant production of vanadium (V) and chromium (Cr). This behavior seems unphysical.

I would appreciate advice on the following points:

  • Can a 10 µm layer thickness lead to geometrical or tracking limitations in FLUKA (e.g., boundary crossing accuracy)?

  • Are there recommended strategies for modeling very thin-layered targets (e.g., geometry definition, region splitting, lattice use)?

  • Should specific transport or production thresholds (e.g., cuts, delta-ray production, heavy fragment transport) be adjusted in this case?

  • Are there best practices for activation scoring (e.g., RESNUCLEi, DCYSCORE, IRRPROFI) in thin targets?

Unfortunately, increasing the foil thickness is not an option, as 10 µm reflects the experimental configuration.

Any guidance on obtaining accurate, reliable activation results in this setup would be greatly appreciated.

Thank you very much for your help.

Best regards,

Rubi

Please provide the used software versions.

FLUKA:
Flair:

Description

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Input files

Please upload all relevant files. (FLUKA input file, Flair project file, user routines, and data files)

2

Note that V and Cr nuclei generated in a Ti foil can migrate to a Zr foil (RESNUCLEi scores the nuclei stopping in the selected region).

3

I had a similar thought, but the magnitude of the observed V and Cr production still seems too large to be explained by this effect alone.

4

Too large with respect to which reference?
You may want to upload your input file for crosscheck.
To get a more accurate transport of alphas and recoils, a PART-THR card setting a cutoff of few keV for 4-HELIUM (which applies automatically to all other ions, in terms of the same keV/n value) is suitable.

5

main.inp (10.8 KB)

Please find attached my input. I am also thinking of adding the STEPSIZE card. What do you think?

STEPSIZE 1E-7 1E-6 Tifoil01 Zrfoil04

6

FLUKA cross sections for V and Cr production by low-energy alphas on Ti look in pretty reasonable agreement with available data, while the contribution from reactions on Zr is irrelevant. The V/Cr activity you observe in the Zr foils is indeed a transport effect.

Your input contains several pointless cards (PHYSICS/PEATHRES, PHYSICS/IONSPLIT, MUPHOTON, PHOTONUC, PAIRBREM, LOW-PWXS, …). Just add the aforementioned PART-THR.

Moreover, note that your definition of natural zirconium is wrong, since it’s given in atom (rather than mass) fractions. Especially, it’s useless, since it’s enough to input a MATERIAL card with Z=40 (and zirconium density and name) and A blank, which automatically assumes natural composition.