Elastic scattering 20 MeV neutrons


I have the following problem: I am shooting 20 MeV neutrons and looking at the cross sections for elastic and inelastic scattering. I am including, two graphs: FLUKA and GEANT4. G4 is when the elastic scattering has 3 peaks. The binning here is logarithmic. When comparing this to FLUKA measurements, it seems that the elastic scattering should not have 3 peaks, but just 1 and little bit. I have obtained the same results with QGSP_BIC_HP, QGSP_BERT_HP, QGSP_INCLXX_HP, QGSP_BIC_HP. When shooting the protons at 20 MeV, the elastic scattering has very similar features. Does anyone have an idea, why are there differences and which of the approaches is the right one?

Thank you!

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20 MeV is exactly the limit that the FLUKA code (and I think also G4) switches from models to databases. It maybe better to do the comparison slightly below/above 20MeV e.g. 19.9 and for 20.1 MeV

Hello Vasilis, thank you so much for the answer!
Just to make sure I understand: FLUKA and Geant4 uses models (I suppose the ChipsElasticXS) below 20 MeV and ENDF databases >20 MeV? Thank you so much for the answer!

The opposite, models for Eneutron>20MeV and ENDF-databases for Eneutron<20MeV (at least for FLUKA).
I know that there are some databases that extend above the 20MeV FLUKA is not using them but I don’t know for Geant if it uses them.

just to complete Vasilis’ answer for fluka…

the didactic one: https://indico.cern.ch/event/694979/contributions/2927113/attachments/1657643/2654314/LowEnergyNeutrons_2018.pdf
the official version: The official FLUKA site: FLUKA Online Manual