Hadronic and Electromagnetic Physics: special applications V.Ivanchenko BINP, Novosibirsk, Russia & CERN, Geneve, Switzerland

Feb, 18-22, 2002G4 User Workshop, SLAC2 Introduction The purpose of this talk is to discuss several specific Geant4 usecases and to try to answer on some frequently asked questions: Can hadronic and electromagnetic physics be completely separated? For what usecases hadronic physics can be dropped? Is hadronic physics important for lowenergy applications?

Feb, 18-22, 2002G4 User Workshop, SLAC3 Hadronic and Electromagnetic Physics In Geant4 EM physics is implemented as a set of processes, which are responsible as for cross sections and for generation of secondary particles A combination of several models are hidden inside processes Alternative processes are available Cross sections and secondary generators are separated for hadronic processes Different models can be used for a given particle in one run There are significant common validity ranges of different models

Feb, 18-22, 2002G4 User Workshop, SLAC4 Electromagnetic processes Standard and lowenergy processes (ionisation and Bremsstrahlung) for electron energy loss can be used Standard is faster but lowenergy is more precise

Feb, 18-22, 2002G4 User Workshop, SLAC5 Hadronic physics Elastic and inelastic processes are available A set of models intend to generate secondary particles in hadron – nucleus inelastic interactions Different models cover different energy ranges User have to identify the optimal combination of models for his/her usecase There is one exception – nuclear interaction is implemented in EM domain (see next slide)

Feb, 18-22, 2002G4 User Workshop, SLAC6 Nuclear stopping power Heavy charged particles loose energy mainly to ionization (Electronic stopping power) – energy is transform to atomic electrons. In G4 two alternative processes are in charge for: G4hIonisation G4hLowEnergyIonisation Heavy charged particles scattered on the atomic nuclei. This process can be simulated in G4 using Elastic hadronic processes

Feb, 18-22, 2002G4 User Workshop, SLAC7 Nuclear stopping power At low energy the number of elastic collisions is huge. To take this energy losses into account Nuclear stopping power approach is used. It is an example of non ionizing energy loss

Feb, 18-22, 2002G4 User Workshop, SLAC8 Nuclear stopping power In Geant4 Nuclear stopping power is implemented currently as a part of total energy loss in the process –G4hLowEnergyIonisation User can enable/disable nuclear stopping using methods –SetNuclearStoppingOn –SetNuclearStoppingOff

Feb, 18-22, 2002G4 User Workshop, SLAC9 Nuclear stopping power Nuclear stopping power should be taking into account for applications, for which a precision of about 1 microns for simulation of stopping point is required For that the process should be used G4hLowEnergyIonisation

Feb, 18-22, 2002G4 User Workshop, SLAC10 Radiation dose distribution The simulation of radiation dose distribution is required for medical, space, and other applications If hadronic processes are ignored in simulation, then the width of the Bragg peak of ionization cannot be reproduced by Geant4 Taking into account hadronic elastic process the experimental data can reasonably reproduced

Feb, 18-22, 2002G4 User Workshop, SLAC11 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

Feb, 18-22, 2002G4 User Workshop, SLAC12 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  /m e ) 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 --

Feb, 18-22, 2002G4 User Workshop, SLAC13 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

Feb, 18-22, 2002G4 User Workshop, SLAC14 Negative muon stopping The electron spectra of captured  - for the decay  -  e -  e is not the same as for the free  - The total energy transfer to electrons and gammas is increased with Z of the host atom AtomICsTl K-shell energy(MeV)

Feb, 18-22, 2002G4 User Workshop, SLAC15 Conclusion Hadronic and electromagnetic processes represents different fundamental interactions In the Geant4 toolkit different packages are designed for simulation of EM and hadronic physics However there are processes in which for different stage of the process EM or hadronic physics is the main driver These processes should be taken into account in some HEP applications For precise G4 simulation both EM and hadronic processes should to be activated even at low energies