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Geant4: Hadronic Processes 1

This article discusses the various models and cross sections available in Geant4 for simulating hadronic interactions, including nuclear reactions, stopping of charged particles, negative muon stopping, pion stopping, and fragmentation of hadronic systems. It provides an overview of the models and their applications, as well as the need for tuning and combining different models.

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Geant4: Hadronic Processes 1

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  1. Geant4:Hadronic Processes 1 Cross sections Secondary generators Nuclear interactions at rest CHIPS model 16.07.02 Salamanca

  2. Model approach – cross sections and secondary generation are separated. Based of evaluated data libraries: ENDF, Jef, EFF, JENDL, FENDL, CENDL, ENSDF, Brond, and MENDL. Following models are exist now: Elastic cascade Chiral_inv_phase_space Pre-equilibrium High_energy parameterized Low_energy parameterized Isotope_production Neutron_hp Stopping Radiative_decay String fragmentation MARS-17 Geant4 hadronics 16.07.02 Salamanca

  3. Geant4 Hadronics 16.07.02 Salamanca

  4. Geant4 cross sections • Cross elastic and inelastic cross sections are based on Geant3 data • Advance parametrisations are provided for p, n, , e–, and  nuclear reactions • To access the database on nuclear levels required for simulation of nuclear deexcitations environment variable should be defined: G4LEVELGAMMADATA • G4NDL0.2 – without neutron transport • G4NDL3.7 – with neutron transport 16.07.02 Salamanca

  5. Hadronic PhysicsList • G4ParticleDefinition * n = G4Neutron::Neutron(); • G4ProcessManager * m = n->GetProcessManager(); • G4NeutronInelasticProcess * thePr = new G4NeutronInelasticProcess(“neuInelastic”); • m->AddDiscreteProcess(thePr); • thePr->GetCrossSectionDataStore()-> AddDataSet(new G4NeutronHPInelasticData()); • thePr->RegisterMe(new G4NeutronHPInelasticModel()) 16.07.02 Salamanca

  6. Hadronic PhysicsList • Default cross sections are defined • Default models are not defined • Several models can be added to a process • Energy ranges of models must not intersect 16.07.02 Salamanca

  7. Stopping of negatively charged particles • Negatively charged particles (-, -, K-) loss their energy to ionization and captured by atomic nuclei • Excited nuclear emits nucleons • G4VRestProcess – abstract interface to these processes • They are implemented in G4 hadronic package • Electromagnetic interactions have to be taken into account as well 16.07.02 Salamanca

  8. Negative muon stopping • The process was described by E.Fermi and E.Teller in 1947 • Stopping - is captured by the host atom into high orbital momentum state of the mesonic atom with a principal quantum number n = (m/me)1/2  14 • Then muon cascade down to K-shell of the mesonic atom • Auger transitions are dominant for higher orbits • For low orbits radiative dipole transitions dominate - Z 16.07.02 Salamanca

  9. Negative muon stopping • As a result, Auger electrons and gamma-rays are emitted by the host atoms • On the K-shell muon decays or is captured by the nucleus • Life time is differ from that of free muon • For atom with Z = 11 these two processes have the same probability • The process G4MuonMinusCaptureAtRest can be used for G4 simulation 16.07.02 Salamanca

  10. Stopping of – • Negative pions are captured by atomic nucleus before the end of mesonic atom cascade • Two different models: evaporation and absorption describe the neutron spectrum 16.07.02 Salamanca

  11. Stopping of pbar • Chiral Invariant Phase Space Model (CHIPS) • Branching ratios of final states are reproduced with very high accuracy • These data were not used in the model! 16.07.02 Salamanca

  12. Fragmentation of excited hadronic system into hadrons Based on quark-parton model and asymptotic freedom approach Assumes massless quarks Use quark exchange probability and probability of hadronisation Temperature of hadonic system is a fundamental parameter of the model CHIPS model 16.07.02 Salamanca

  13. The probability to find a system of N partons with the mass M at temperature T dW~M2N-4e-M/TdM Automatic energy/ momentum balance Residual nucleus production Is applicable to all reactions Is tuned inside G4 for  and pbar capture; Is tuned for -nuclear reactions (giant dipole resonance, delta resonance, and continum) CHIPS model 16.07.02 Salamanca

  14. CHIPS model • Is tuned inside G4 for electron-nucleus interactions based on equivalent photons approach • Is not tuned for hadron nuclear interactions, need tuning or combining with other models responsible for scattering of incident hadrons on nuclei 16.07.02 Salamanca

  15. Conclusion remarks • Geant4 toolkit includes a set of models to simulate hadron-nucleus interactions • Models are applicable to different use cases and to different energy ranges • To built optimal combinations of models and cross sections user should know what physics required for his/her application • It is the most complicate domain of G4! 16.07.02 Salamanca

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