Comparison of the projectile fragmentation reaction in GEANT4 against EPAX formula for rare isotopes studies*

The study of unstable nuclei far from β-stability through fragmentation of heavy-ion beams is one of the most used approaches in low to intermediate energy nuclear physics to gain insights into their nuclear structure and the reaction mechanisms. 

The Facility for Rare Isotope Beams uses intensively the LISE⁺⁺ and GEANT4 tools to model experimental setups. However, there is so far no comprehensive and systematic validation of these two methods against each other. A powerful formula to calculate the fragmenting projectile cross section down to a few milli or nano-barn, called EPAX (Empirical Parametrized CROSS section) is implemented in LISE⁺⁺ and is based on experimental data existing in the literature. In this communication, we will present a comparative study of the distributions of the total cross section of the fragment nuclei between GEANT4 hadronic physics models and EPAX using LISE⁺⁺ interface.

To perform this study, a 140 MeV/u beam of ⁴⁰Ar is used to impinge a ⁹Be target through the fragmentation process. Five GEANT4 physics models (e.g., Shielding, QGSP_BERT, QGSP_BIC, FTFP_BERT and QBBC) have been identified as adequate to describe these reactions. Their predictions are compared to those from EPAX.

The identification of the discrepancies between GEANT4 and EPAX for rare isotopes will lead to the development of a systematic validation suite to benchmark each code for their future versions. This will allow also to offer guidance for their usage to low- and high-energy nuclear physics communities.