geant4 collaboration 1 electromagnetic physics authors: p. gumplinger, m. maire, p. nieminen, m.g....

Geant4 Collaboration 1

Electromagnetic PhysicsElectromagnetic Physics

Authors: P. Gumplinger, M. Maire, P. Nieminen, M.G. Pia, L. Urban

Budker Inst. of PhysicsIHEP ProtvinoMEPHI Moscow Pittsburg University

Extended introduction


Electromagnetic physicsElectromagnetic physics

It handles electrons and positrons , X-ray and optical photons muons charged hadrons ions

Comparable to Geant3 already in the 1st release (1997)

High energy extensionsHigh energy extensions fundamental for LHC experiments, cosmic ray experiments

etc.

Low energy extensionsLow energy extensions fundamental for space and medical applications, neutrino

experiments, antimatter spectroscopy etc.

Alternative models for the same physics processAlternative models for the same physics process

energy loss

multiple scattering Cherenkov transition radiation ionisation Bremsstrahlung annihilation photoelectric effect Compton scattering Rayleigh effect conversion e+e- pair production refraction reflection absorption scintillation synchrotron radiation fluorescence Auger effect (in progress)


OO designOO design

Alternative models, obeying the same abstract interface, are provided for the same physics interaction

Top level class diagram of electromagnetic physics


OO design of Low Energy e.m. processes: generalOO design of Low Energy e.m. processes: general


OO design of Low Energy e.m. processes: photonsOO design of Low Energy e.m. processes: photons


OO design of Low Energy e.m. processes: electronsOO design of Low Energy e.m. processes: electrons


OO design of Low Energy e.m. processes: hadronsOO design of Low Energy e.m. processes: hadrons


Production thresholdsProduction thresholds

No tracking cuts, only production thresholdsproduction thresholds thresholds for producing secondaries are expressed in rangerange,

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


Effect of production thresholdsEffect of production thresholds

PbLiquid

Ar

Liquid ArPb

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

In Geant3Geant3DCUTE = 455 keV

DCUTE = 2 MeV


An example how to set cut valuesAn example how to set cut valuesvoid 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();}


Standard electromagnetic processesStandard electromagnetic processes

PhotonsPhotons Compton scattering conversion photoelectric effect

Electrons and positronsElectrons and positrons Bremsstrahlung ionisation

continuous energy loss from Bremsstrahlung and ionisation

ray production positron annihilation synchrotron radiation

Charged hadronsCharged hadrons

Shower profile, 1 GeV e- in water

J&H Crannel - Phys. Rev. 184-2 August69


Features of Standard e.m. processesFeatures of Standard e.m. processes

Multiple scatteringMultiple scattering new model computes mean free path length and

lateral displacement

Ionisation featuresIonisation features optimize the generation of rays near

boundaries

Variety of modelsVariety of models for ionisation and energy loss

including the PhotoAbsorption Interaction model

Differential and Integral approachDifferential 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. 148. (1978) 399


Ionisation energy loss distribution produced by pions, PAI modelPAI model

3 GeV/c in 1.5 cm Ar+CH4 5 GeV/c in 20.5 m Si

Ionisation energy loss produced by charged particles in thin layers of absorbers

PPhoto hoto AAbsorption bsorption IIonisation Modelonisation Model


Low energy e.m. Low energy e.m. extensionsextensions

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


Low energy extensions: eLow energy extensions: e--, ,

Based on EPDL97, EEDL and EADL evaluated data libraries

cross sections sampling of the final state

Photoelectric effect Compton scattering Rayleigh scattering Bremsstrahlung Ionisation Fluorescence

250 250 eV up to 100 GeVeV up to 100 GeV

Geant3.21

Geant4

C, N, O line emissions included

10 keV limit

250 eV limit


0.01 0.1 1 100.01

0.1

1

10

100

1000

Geant4 LowEn NIST

/

(cm

2 /g

) in

iron

Photon Energy (MeV)

Fe

0.01 0.1 1 10-16

-14

-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

14

16

Delta = (NIST-G4EMStand) / NIST

Delta = (NIST-G4LowEn) / NIST

Del

ta (

%)

Photon Energy (MeV)

water

Photon attenuation coefficientPhoton attenuation coefficient

Comparison of Geant4 electromagnetic processes with NIST data :Standard and Low Energy processes

Example of application of Example of application of Geant4 Low Energy e.m. Geant4 Low Energy e.m.

processesprocesses


Low energy extensions: hadrons and ionsLow 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 chargeVarious models, depending on the energy range and the charge


Muon processesMuon 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

Validity range: 1 keV up to 1000 PeV scale1 keV up to 1000 PeV scale


Processes for optical photonsProcesses 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 Geant4Processes in Geant4 in-flight absorption Rayleigh scattering reflection and refraction on

medium boundaries Track of a photon entering a light concentrator CTF-Borexino


Examples of application of Geant4 e.m. physicsExamples 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


Standard electromagnetic process classes (1)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


Standard electromagnetic process classes (2)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


Low Energy electromagnetic process classesLow 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)


Muon process classesMuon 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 classesX-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


Other practical detailsOther 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


If you want to learn more...If you want to learn more... Low Energy Electromagnetic Physics homepage http://www.ge.infn.it/geant4/lowE/index.html

Gallery of electromagnetic physics documentation and results http://wwwinfo.cern.ch/asd/geant4/reports/gallery/

User's Guide: For Application Developers http://wwwinfo.cern.ch/asd/geant4/G4UsersDocuments/

UsersGuides/ForApplicationDeveloper/html/index.html

User's Guide: For Toolkit Developers http://wwwinfo.cern.ch/asd/geant4/G4UsersDocuments/

UsersGuides/ForToolkitDeveloper/html/index.html

Physics Reference Manual http://wwwinfo.cern.ch/asd/geant4/G4UsersDocuments/

UsersGuides/PhysicsReferenceManual/html/PhysicsReferenceManual.html


Geant4 examples illustrating Geant4 examples illustrating electromagnetic physics electromagnetic physics

Novice examplesNovice examples N02: Simplified tracker geometry with uniform magnetic field N03: Simplified calorimeter geometry N04: Simplified collider detector with a readout geometry

Advanced examplesAdvanced examples xray_telescope: Typical X-ray telescope gammaray_telescope: Typical ray telescope brachytherapy: Medical physics application