Low Energy Electromagnetic Physics PART II

1
Low Energy Electromagnetic Physics PART II

• Alex Howard
• Imperial College, UK
• a.s.howard_at_ic.ac.uk
• on behalf of the Low Energy Electromagnetic
  Working Group
• Geant4 User Workshop
• CERN, 11-15 November 2002

http//www.ge.infn.it/geant4/training/
2
Plan of the tutorial

• Lecture 1
• Overview
• Software process
• OOAD
• Physics
• Electrons and photons
• Hadrons and ions
• Atomic relaxation
• Polarisation

• Lecture 2
• How to use LowE processes
• Examples
• Experimental applications
• Outlook

3
Outline

• How to use Geant4 LowE electromagnetic processes
• Where to find examples
• A selection of real-life applications
• Space Physics X-Rays
• Space Physics Proof Mass Charging
• Medical Physics
• Dark Matter
• Outlook
• New Physics
• Performance Optimisation
• Conclusions

4
Low Energy Em Physics Implementation

• The following code is required in
  yourPhysicsList.cc
• All code has been lifted from the relevant
  advanced examples

• Compton scattering
• Rayleigh scattering
• Photoelectric effect
• Pair production
• Bremsstrahlung
• Ionisation
• Polarised Compton
• atomic relaxation
• fluorescence
• Auger effect
• following photoelectric effect and ionisation

5
brachytherapy

• Low energy electromagnetic processes for precise
  calculation of dose distribution
• // gamma
• include "G4LowEnergyRayleigh.hh"
• include "G4LowEnergyPhotoElectric.hh"
• include "G4LowEnergyCompton.hh"
• include "G4LowEnergyGammaConversion.hh"
• // e-
• include "G4LowEnergyIonisation.hh"
• include "G4LowEnergyBremsstrahlung.hh"
• // e
• include "G4eIonisation.hh"
• include "G4eBremsstrahlung.hh"
• include "G4eplusAnnihilation.hh"

6
Brachytherapy Implementation
void BrachyPhysicsListConstructEM()
theParticleIterator-gtreset() while(
(theParticleIterator)() )
G4ParticleDefinition particle
theParticleIterator-gtvalue()
G4ProcessManager pmanager particle-gtGetProcessM
anager() G4String particleName
particle-gtGetParticleName() //processes
lowePhot new G4LowEnergyPhotoElectric("LowEnPho
toElec") loweIon new G4LowEnergyIonisation
("LowEnergyIoni") loweBrem new
G4LowEnergyBremsstrahlung("LowEnBrem") if
(particleName "gamma") //gamma
pmanager-gtAddDiscreteProcess(new
G4LowEnergyRayleigh) pmanager-gtAddDiscreteP
rocess(lowePhot) pmanager-gtAddDiscreteProce
ss(new G4LowEnergyCompton)
pmanager-gtAddDiscreteProcess(new
G4LowEnergyGammaConversion)  
else if (particleName "e-")
//electron pmanager-gtAddProcess(new
G4MultipleScattering, -1, 1,1)
pmanager-gtAddProcess(loweIon, -1, 2,2)
pmanager-gtAddProcess(loweBrem, -1,-1,3)
else if (particleName "e")
//positron pmanager-gtAddProcess(new
G4MultipleScattering, -1, 1,1)
pmanager-gtAddProcess(new G4eIonisation,
-1, 2,2) pmanager-gtAddProcess(new
G4eBremsstrahlung, -1,-1,3)
pmanager-gtAddProcess(new G4eplusAnnihilation,
0,-1,4)
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X-ray fluorescence

• Physics Low Energy processes, atomic relaxation
• include "G4LowEnergyCompton.hh"
• include "G4LowEnergyGammaConversion.hh"
• include "G4LowEnergyPhotoElectric.hh"
• include "G4LowEnergyRayleigh.hh"
•  
• // e
• include "G4MultipleScattering.hh"
• include "G4eIonisation.hh"
• include "G4eBremsstrahlung.hh"
• include "G4eplusAnnihilation.hh"
•  
• include "G4LowEnergyIonisation.hh"
• include "G4LowEnergyBremsstrahlung.hh"
• include "G4hLowEnergyIonisation.hh"
•  

8
Process Registration X-ray Fluor

• void XrayFluoPhysicsListConstructEM()
• theParticleIterator-gtreset()
• while( (theParticleIterator)() )
• G4ParticleDefinition particle
  theParticleIterator-gtvalue()
• G4ProcessManager pmanager
  particle-gtGetProcessManager()
• G4String particleName particle-gtGetParticleN
  ame()
• if (particleName "gamma")
• // gamma
• pmanager-gtAddDiscreteProcess(new
  G4LowEnergyCompton)
• LePeprocess new G4LowEnergyPhotoElectric()
  
• //LePeprocess-gtActivateAuger(false)
• //LePeprocess-gtSetCutForLowEnSecPhotons(1000
  0 keV)
• //LePeprocess-gtSetCutForLowEnSecElectrons(10
  000 keV)
• pmanager-gtAddDiscreteProcess(LePeprocess)
• pmanager-gtAddDiscreteProcess(new
  G4LowEnergyRayleigh)

else if (particleName "e-")
//electron pmanager-gtAddProcess(new
G4MultipleScattering,-1, 1,1) LeIoprocess
new G4LowEnergyIonisation()
//LeIoprocess-gtActivateAuger(false)
//LeIoprocess-gtSetCutForLowEnSecPhotons(10000
keV) //LeIoprocess-gtSetCutForLowEnSecElectr
ons(10000 keV) pmanager-gtAddProcess(LeIopro
cess, -1, 2, 2) LeBrprocess new
G4LowEnergyBremsstrahlung()
pmanager-gtAddProcess(LeBrprocess, -1, -1, 3)
else if (particleName "e")
//positron pmanager-gtAddProcess(new
G4MultipleScattering,-1, 1,1)
pmanager-gtAddProcess(new G4eIonisation, -1,
2,2) pmanager-gtAddProcess(new
G4eBremsstrahlung, -1,-1,3)
pmanager-gtAddProcess(new G4eplusAnnihilation,
0,-1,4)

• else if (particleName "proton")
• //proton
• pmanager-gtAddProcess(new G4MultipleScatterin
  g,-1,1,1)
• pmanager-gtAddProcess(new G4hLowEnergyIonisat
  ion,-1, 2,2)
• else if ( particleName "alpha" )
• pmanager-gtAddProcess(new G4MultipleScattering,-1,
  1,1)
• G4hLowEnergyIonisation iIon new
  G4hLowEnergyIonisation()
• pmanager-gtAddProcess(iIon,-1,2,2)

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Underground physics

• // Electromagnetic Processes // all charged
  particles
•  
• // gamma
• include "G4LowEnergyRayleigh.hh"
• include "G4LowEnergyPhotoElectric.hh"
• include "G4LowEnergyCompton.hh"
• include "G4LowEnergyGammaConversion.hh"
•  
• // e-
• include "G4LowEnergyIonisation.hh"
• include "G4LowEnergyBremsstrahlung.hh"
•  
• // e
• include "G4eIonisation.hh"
• include "G4eBremsstrahlung.hh"
• include "G4eplusAnnihilation.hh"
•  
•  
• // alpha and GenericIon and deuterons, triton,
  He3

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Process Creation - DMX

• void DMXPhysicsListConstructEM()
•  
• // processes
• G4MultipleScattering aMultipleScattering new
  G4MultipleScattering()
•  
• G4LowEnergyPhotoElectric lowePhot new
  G4LowEnergyPhotoElectric()
• G4LowEnergyIonisation loweIon new
  G4LowEnergyIonisation()
• G4LowEnergyBremsstrahlung loweBrem new
  G4LowEnergyBremsstrahlung()
• // fluorescence specific cuts for flourescence
• // from photons, electrons and bremsstrahlung
  photons
•  
• G4double fluorcut 250eV
• lowePhot-gtSetCutForLowEnSecPhotons(fluorcut)
• loweIon -gtSetCutForLowEnSecPhotons(fluorcut)
• loweBrem-gtSetCutForLowEnSecPhotons(fluorcut)
•  
•  

11
Hadron Ionisation Choosing a model

• G4hLowEnergyIonisation ahadronLowEIon new
  G4hLowEnergyIonisation()
• ahadronLowEIon-gtSetNuclearStoppingPowerModel("IC
  RU_R49")
• ahadronLowEIon-gtSetNuclearStoppingOn()
•  
• // ahadronLowEIon-gtSetElectronicStoppingPower
  Model
• // (G4GenericIonGenericIonDefinition(),
  "ICRU_R49p")
• // ahadronLowEIon-gtSetElectronicStoppingPower
  Model
• // (G4ProtonProtonDefinition(),
  "ICRU_R49p")
• // Switch off the Barkas and Bloch corrections
• ahadronLowEIon-gtSetBarkasOff()
• // Switch off hadron-induced fluorescence (for
  now)
• ahadronLowEIon-gtSetFluorescence(false)
• // NOTE the same G4hLowEnergyIonisation
  process is applied to all hadrons, which need not
  be the case!

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Attaching Processes to Particles

• theParticleIterator-gtreset()
• while( (theParticleIterator)() )
• G4ParticleDefinition particle
  theParticleIterator-gtvalue()
•  
• G4ProcessManager pmanager
  particle-gtGetProcessManager()
• G4String particleName
  particle-gtGetParticleName()
• G4String particleType
  particle-gtGetParticleType()
• G4double particleCharge
  particle-gtGetPDGCharge()
• // gamma
• if (particleName "gamma")
• pmanager-gtAddDiscreteProcess(new
  G4LowEnergyRayleigh())
• pmanager-gtAddDiscreteProcess(lowePhot)
• pmanager-gtAddDiscreteProcess(new
  G4LowEnergyCompton())
• pmanager-gtAddDiscreteProcess(new
  G4LowEnergyGammaConversion())

13
Attaching Processes to Particles

• // electron
• else if (particleName "e-")
• // process ordering AddProcess(name, at
  rest, along step, post step)
• // -1 not implemented, then ordering
• pmanager-gtAddProcess(aMultipleScattering,
  -1, 1, 1)
• pmanager-gtAddProcess(loweIon,
  -1, 2, 2)
• pmanager-gtAddProcess(loweBrem,
  -1,-1, 3)
• // positron
• else if (particleName "e")
• pmanager-gtAddProcess(aMultipleScattering,
  -1, 1, 1)
• pmanager-gtAddProcess(new G4eIonisation(),
  -1, 2, 2)
• pmanager-gtAddProcess(new
  G4eBremsstrahlung(), -1,-1, 3)
• pmanager-gtAddProcess(new
  G4eplusAnnihilation(), 0,-1, 4)

14
Attaching Processes to Particles

• // muons
• else if( particleName "mu"
• particleName "mu-" )
• pmanager-gtAddProcess(aMultipleScattering,
  -1, 1, 1)
• pmanager-gtAddProcess(new
  G4MuIonisation(), -1, 2, 2)
• pmanager-gtAddProcess(new
  G4MuBremsstrahlung(), -1,-1, 3)
• pmanager-gtAddProcess(new
  G4MuPairProduction(), -1,-1, 4)
• if( particleName "mu-" )
• pmanager-gtAddProcess(new
  G4MuonMinusCaptureAtRest(), 0,-1,-1)
• // charged hadrons
• else if (particleName "proton"
• particleName "alpha"
• particleName "deuteron"
• particleName "triton"
• particleName "He3"
• particleName "GenericIon"
• (particleType "nucleus"
  particleCharge ! 0))

15
Attaching Processes to Particles

• // OBJECT may be dynamically created as
  either a GenericIon or nucleus
• pmanager-gtAddProcess(aMultipleScattering,
  -1, 1, 1)
• pmanager-gtAddProcess(ahadronLowEIon,
  -1, 2, 2)
• // all other charged particles except
  geantino
• else if ((!particle-gtIsShortLived())
• (particleCharge ! 0.0)
• (particleName !
  "chargedgeantino"))
• pmanager-gtAddProcess(aMultipleScattering,
  -1, 1, 1)
• pmanager-gtAddProcess(ahadronLowEIon,
  -1, 2, 2)
•  

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Setting Energy Cuts

• //special for low energy physics
• G4double lowlimit250eV
• G4Gamma SetEnergyRange(lowlimit,100GeV)
• G4ElectronSetEnergyRange(lowlimit,100GeV)
• G4PositronSetEnergyRange(lowlimit,100GeV)
  

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Validation of Low Energy Physics Some (biased)
examples

• Two examples of Low Energy Physics Implementation
  and Validation that I have experience in
• UNDERGROUND (DARK MATTER) SIMULATION DMX
• Low energy gammas, electrons, hadrons and
  secondary production
• GRAVITATIONAL WAVE LISA (Proof Mass Charging)
• All electromagnetic processes that can lead to
  residual charge,
• In particular secondary production

18
g
upwards
through
Xe shell
Pb compton
19
241Am spectrum
experimental
20
g spectrum
experimental
21
Time Constant Discrimination
Geant4 Output
Experimental Data

• Red Curve Alphas
• Blue Curve Gammas

22
Geant4 Simulationof Test-Mass Chargingin the
LISA Mission
     

• Very long base-line 1 million km
• Very high precision lt 1nm 1pm (!)

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Physics List
EM processes (LowE) Electrons, Gammas, etc Atomic
de-excitation Hadrons (no hFluorescence)
Secondaries Cuts (250 eV), 1mm - 5mm Kill e-
outside caging
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Results I
45 s exposure 10,000,000 events 1 charging
event 2,000 events 40,000 events/day/CPU
Charging rate
G4 result 58 e/s
(G3 result 11 e/s)
52 e/s
6 e/s
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Results II
Cuts
1 um 8.77 keV 41 e/s
(0.1 um) 250 eV 52 e/s
2 um 30.7 keV 40 e/s
5 um 53.2 keV 42 e/s
Energy of Primary, MeV
Decreasing the production threshold from 10 keV
(G3, G4EM) to 250 eV (G4LowE) leads to a 20
increase of the charging rate!
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Other Users SPACE and Cosmic Ray
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The Future

• In progress
• Polarised g conversion, photoelectric
• More precise angular distributions (Rayleigh,
  photoelectric, Bremsstrahlung etc.)
• Foreseen
• New models, based on different physics approaches
• Processes for positrons
• Performance Optimisation and Enhancement
• Development plan
• Driven by user requirements
• Schedule compatible with available resources

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To learn more
Conclusions

• Low Energy EM Physics implementation has been
  demonstrated
• Its use within actual examples demonstrate
• Validation with experimental data has been
  carried out (ongoing)
• There are still low energy EM physics areas that
  are being developed
• Performance optimisation, benchmarking and
  testing are being initiated.

• Geant4 Physics Reference Manual
• Application Developer Guide
• http//www.ge.infn.it/geant4/lowE