Antiproton Annihilations/Scattering

Physics, Transport and Magnetic Fields
1

Dear FLUKA experts,

I am using FLUKA/Flair to simulate a beam of low energetic (250 eV) antiprotons interacting with a thin (2 um) foil. In my simulations 100 % of the antiprotons annihilate on the foil and none are scattering off it.
I have also done the same simulations in Geant4 using FTFP_BERT_EMZ and there only about 50 % of the antiprotons are annihilating. Is this just a difference in the simulation models or am I missing some physics that I would need to activate?

Thank you!

2

250 eV is below the minimum transport threshold of 1 keV (PRECISIO DEFAULTS is 100 keV, but the PART-THR card allows one to go down to 1 keV), under which stopping power calculation does no longer hold. Therefore, by construction all antiprotons stop in the foil and so annihilate. The picture may change above 1 keV, as soon as the estimated range exceeds the foil thickness.