Evaluation on Geant4 Hadronic Models for Pion Minus, Pion Plus and Neutron Particles as Major Antiproton Annihilation Products

Geant4 is an open source simulation toolkit based on c++, which its advantages progressively lead to applications in research domainsespecially modeling the biological effects of ionizing radiation at the sub cellular scale. however, it was shown that geant4 does notgive a reasonable result in the prediction of antiproton dose especially in bragg peak. one of the reasons could be lack of reliablephysic model to predict the final states of annihilation products like pions. since most of the antiproton deposited dose is resulted fromhigh let nuclear fragments following pion interaction in surrounding nucleons and we tried to reproduce depth dose curves of mostprobable energy range of pions and neutron particle using geant4. we consider this work one of the steps to understand the origin ofthe error and finally verification of geant4 for antiproton tracking. geant4 toolkit version 9.4.6.p01 and fluka version 2006.3 were usedto reproduce the depth dose curves of 220 mev pions (both negative and positive) and 70 mev neutrons. the geometry applied in thesimulations consist a 20 × 20 × 20 cm water tank, similar to that used in cern for antiproton relative dose measurements. differentphysic lists including quark gluon string precompound (qgsp) binary cascade (bic) hp, the recommended setting for hadrontherapy, were used. in the case of pions, geant4 resulted in at least 5% dose discrepancy between different physic lists at depth closeto the entrance point. even up to 15% discrepancy was found in some cases like qbbc compared to qgsp bic hp. a significantdifference was observed in dose profiles of different geant4 physic list at small depths for a beam of pions. in the case of neutrons,large dose discrepancy was observed when lhep or lhep_emv lists were applied. the magnitude of this dose discrepancy couldbe even 50% greater than the dose calculated by lhep (or lhep_emv) at larger depths. we found that effect different geant4 physiclist in reproducing depth dose profile of the beam of pions was not negligible. because the discrepancies were pronounced in smallerdepth and also regarding the contribution of pions in deposited dose of a beam of antiproton, further investigation on choosing mostsuitable and accurate physic list for this purpose should be done. furthermore, this study showed careful attention must be paid tochoose the appropriate geant4 physic list for neutron tracking depending to the applications criteria. we failed to find any agreementbetween results from geant4 and fluka to reproduce depth dose profile of pion with the energy range used in this study.3