Geant4 Collaboration 1 Electromagnetic Physics Authors: P. Gumplinger, M. Maire, P. Nieminen, M.G. Pia, L. Urban Budker Inst. of Physics IHEP Protvino MEPHI Moscow Pittsburg University Extended introduction

Geant4 Collaboration 2 Electromagnetic physics It handles l electrons and positrons , X-ray and optical photons l muons l charged hadrons l ions Comparable to Geant3 already in the 1st  release (1997)  High energy extensions l fundamental for LHC experiments, cosmic ray experiments etc.  Low energy extensions l fundamental for space and medical applications, neutrino experiments, antimatter spectroscopy etc.  Alternative models for the same physics process energy loss 3 multiple scattering 3 Cherenkov 3 transition radiation 3 ionisation 3 Bremsstrahlung 3 annihilation 3 photoelectric effect 3 Compton scattering 3 Rayleigh effect   conversion 3 e + e - pair production 3 refraction 3 reflection 3 absorption 3 scintillation 3 synchrotron radiation 3 fluorescence 3 Auger effect (in progress)

Geant4 Collaboration 3 OO design Alternative models, obeying the same abstract interface, are provided for the same physics interaction Top level class diagram of electromagnetic physics

Geant4 Collaboration 4 OO design of Low Energy e.m. processes: general

Geant4 Collaboration 5 OO design of Low Energy e.m. processes: photons

Geant4 Collaboration 6 OO design of Low Energy e.m. processes: electrons

Geant4 Collaboration 7 OO design of Low Energy e.m. processes: hadrons

Geant4 Collaboration 8 Production thresholds production thresholds  No tracking cuts, only production thresholds range thresholds for producing secondaries are expressed in range, universal for all media converted into energy for each particle and material  It makes better sense to use the range cut-off Range of 10 keV gamma in Si ~ a few cm Range of 10 keV electron in Si ~ a few micron

Geant4 Collaboration 9 Effect of production thresholds Pb Liquid Ar Liquid Ar Pb 500 MeV incident proton Threshold in range: 1.5 mm 455 keV electron energy in liquid Ar 2 MeV electron energy in Pb one must set the cut for delta-rays (DCUTE) either to the Liquid Argon value, thus producing many small unnecessary  -rays in Pb, or to the Pb value, thus killing the  - rays production everywhere Geant3 In Geant3 DCUTE = 455 keV DCUTE = 2 MeV

Geant4 Collaboration 10 An example how to set cut values void ExN03PhysicsList::SetCuts() { if (verboseLevel >1) G4cout << "ExN03PhysicsList::SetCuts:"; // Set cut values for gamma at first and for e- second and next for e+, // because some processes for e+/e- need cut values for gamma SetCutValue(cutForGamma, "gamma"); SetCutValue(cutForElectron, "e-"); SetCutValue(cutForElectron, "e+"); // Set cut values for proton and anti_proton before all other hadrons // because some processes for hadrons need cut values for proton/anti_proton SetCutValue(cutForProton, "proton"); SetCutValue(cutForProton, "anti_proton"); SetCutValueForOthers(defaultCutValue) if (verboseLevel>1) DumpCutValuesTable(); }

Geant4 Collaboration 11 Standard electromagnetic processes  Photons Compton scattering  conversion photoelectric effect  Electrons and positrons Bremsstrahlung ionisation continuous energy loss from Bremsstrahlung and ionisation  ray production positron annihilation synchrotron radiation  Charged hadrons Shower profile, 1 GeV e - in water J&H Crannel - Phys. Rev August69

Geant4 Collaboration 12 Features of Standard e.m. processes  Multiple scattering new model computes mean free path length and lateral displacement  Ionisation features optimize the generation of  rays near boundaries  Variety of models  Variety of models for ionisation and energy loss including the PhotoAbsorption Interaction model  Differential and Integral approach for ionisation, Bremsstrahlung, positron annihilation, energy loss and multiple scattering Multiple scattering 6.56 MeV proton, 92.6 mm Si J.Vincour and P.Bem Nucl.Instr.Meth (1978) 399

Geant4 Collaboration 13 PAI model Ionisation energy loss distribution produced by pions, PAI model 3 GeV/c  in 1.5 cm Ar+CH45 GeV/c  in 20.5  m Si Ionisation energy loss produced by charged particles in thin layers of absorbers Photo Absorption Ionisation Model

Geant4 Collaboration 14 Low energy e.m. extensions e,  down to 250 eV Geant3 down to 10 keV (positrons in progress) Fundamental for space and medical applications, neutrino experiments, antimatter spectroscopy etc. Low energy hadrons and ions models based on Ziegler and ICRU data and parameterisations Barkas effect: models for antiprotons Photon transmission on 1 mm Al

Geant4 Collaboration 15 Low energy extensions: e -,   Based on EPDL97, EEDL and EADL evaluated data libraries l cross sections l sampling of the final state Photoelectric effect Compton scattering Rayleigh scattering Bremsstrahlung Ionisation Fluorescence 250 eV up to 100 GeV Geant3.21 Geant4 C, N, O line emissions included 10 keV limit 250 eV limit

Geant4 Collaboration 16 Fe water Photon attenuation coefficient Comparison of Geant4 electromagnetic processes with NIST data : Standard and Low Energy processes Example of application of Geant4 Low Energy e.m. processes

Geant4 Collaboration 17 Low energy extensions: hadrons and ions  E > 2 MeV  Bethe-Bloch  1 keV < E < 2 MeV  parameterizations Ziegler 1977, 1985 ICRU 1993 corrections due to chemical formulae of materials nuclear stopping power  E < 1 keV  free electron gas model  Barkas effect taken into account quantum harmonic oscillator model Various models, depending on the energy range and the charge

Geant4 Collaboration 18 Muon processes  High energy extensions based on theoretical models  Bremsstrahlung  Ionisation and  ray production  e + e - Pair production  simulation of ultra-high energy and cosmic ray physics 1 keV up to 1000 PeV scale Validity range: 1 keV up to 1000 PeV scale

Geant4 Collaboration 19 Processes for optical photons  Optical photon  its wavelength is much greater than the typical atomic spacing  Production of optical photons in HEP detectors is mainly due to Cherenkov effect and scintillation  Optical properties, e.g. dielectric coefficient, surface smoothness, can be set to a G4LogicalVolume  Processes in Geant4 in-flight absorption Rayleigh scattering reflection and refraction on medium boundaries Track of a photon entering a light concentrator CTF-Borexino

Geant4 Collaboration 20 Examples of application of Geant4 e.m. physics Sampling calorimeter The plot is the visible energy in silicon as a function of the energy of the incident electron The experimental results are from: Sicapo Collaboration, NIM A332 (85-90) 1993

Geant4 Collaboration 21 Standard electromagnetic process classes (1)  Photon processes Compton scattering (class G4ComptonScattering) Gamma conversion (class G4GammaConversion) Photo-electric effect (class G4PhotoElectricEffect)  Electron/positron processes Bremsstrahlung (class G4eBremsstrahlung) Ionisation and delta ray production (class G4eIonisation) Positron annihilation (class G4eplusAnnihilation) Synchrotron radiation (class G4SynchrotronRadiation)  Hadron (e.m.) processes Ionisation (class G4hIonisation)  All charged particles Multiple scattering (class G4MultipleScattering) The ionisation/energy loss of the hadrons can be simulated optionally using the G4PAIonisation/G4PAIenergyLoss classes

Geant4 Collaboration 22 Standard electromagnetic process classes (2)  The (e)ionisation, bremsstrahlung, positron annihilation, energy loss, and multiple scattering processes have been implemented in the so- called “integral approach” as well  The corresponding classes are: G4IeBremsstrahlung G4IeIonisation G4IeplusAnnihilation G4IeEnergyLoss G4IMultipleScattering

Geant4 Collaboration 23 Low Energy electromagnetic process classes  Photon processes Compton scattering (class G4LowEnergyCompton) Rayleigh scattering (class G4LowEnergyRayleigh) Gamma conversion (class G4LowEnergyGammaConversion) Photoelectric effect (class G4LowEnergyPhotoElectric)  Electron processes Bremsstrahlung (class G4LowEnergyBremsstrahlung) Ionisation and delta ray production (class G4LowEnergyIonisation)  Hadron and ion (e.m.) processes Ionisation and delta ray production (class G4hLowEnergyIonisation)

Geant4 Collaboration 24 Muon process classes  Bremsstrahlung (class G4MuBremsstrahlung)  Ionisation and delta ray/knock on electron production (G4MuIonisation)  Nuclear interaction (class G4MuNuclearInteraction)  Direct pair production (class G4MuPairProduction) X-ray production process classes  Cerenkov process (class G4Cerenkov)  Transition radiation (classes G4TransitionRadiation and G4ForwardXrayTR)  The Low Energy electromagnetic processes also produce X-rays through fluorescence

Geant4 Collaboration 25 Other practical details  Data files for the low energy electromagnetic processes are available from the Geant4 Download web page  To use the Low Energy electron and photon processes, the user must set the environment variable $G4LEDATA as the path to the external data set above

Geant4 Collaboration 26 If you want to learn more... Low Energy Electromagnetic Physics homepage Gallery of electromagnetic physics documentation and results User's Guide: For Application Developers ForApplicationDeveloper/html/index.html User's Guide: For Toolkit Developers ForToolkitDeveloper/html/index.html Physics Reference Manual PhysicsReferenceManual/html/PhysicsReferenceManual.html

Geant4 Collaboration 27 If you want to learn more... Low Energy Electromagnetic Physics homepage Gallery of electromagnetic physics documentation and results User's Guide: For Application Developers ForApplicationDeveloper/html/index.html User's Guide: For Toolkit Developers ForToolkitDeveloper/html/index.html Physics Reference Manual PhysicsReferenceManual/html/PhysicsReferenceManual.html

Geant4 Collaboration 28 Geant4 examples illustrating electromagnetic physics Novice examples N02: Simplified tracker geometry with uniform magnetic field N03: Simplified calorimeter geometry N04: Simplified collider detector with a readout geometry Advanced examples xray_telescope: Typical X-ray telescope gammaray_telescope: Typical  ray telescope brachytherapy: Medical physics application