In a very simplified input, alpha or triton of 2 MeV hit a 6x6x1 cm^3 box of pure Argon in a vertical pencil-like beam. The energy deposition spectra inside the gas calculated by FLUKA and GEANT4 look quite different in terms of alphas, revealing a discrepancy > 20%.
I tried in FLUKA by discarding multiple scattering or using single scattering for better accuracy but it doesn’t change the results… Could you please have a look and let me know what is the reason of this disagreement?
Dear Georgios,
the reason of the ~10% ( = 0.2 MeV / 2 MeV) discrepancy you report is the different stopping power recipe. IAEA data for low-energy alpha particles seem actually to indicate an underestimation by FLUKA, which we plan to address.
Best
Thanks so much for your reply.
From https://physics.nist.gov/PhysRefData/Star/Text/ASTAR.html a 2 MeV alpha has a range of 1.52 MeV/cm in pure Argon, while FLUKA gives 1.35 MeV/cm as it can be obtained from the output of the input using DELTARAY card with the PRINT option. Are there any details available concerning the “different” stopping power recipe used in FLUKA and what are the advantages of this recipe compared with what is used in different MC codes?
What you quote are stopping power (not range) values, reflecting the aforementioned ~10% discrepancy. For this specific low-energy alpha case, one may indeed take IAEA data, with which the NIST table is in line, as reference.
