1. Low Energy Electromagnetic Physics PART II
Alex Howard
Imperial College, UK
on behalf of the Low Energy Electromagnetic Working Group
Geant4 User Workshop
CERN, November 2002

2. Plan of the tutorial Lecture 1 Lecture 2 How to use LowE processes
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
} else if (particleName == "e-") {
//electron
pmanager->AddProcess(new G4MultipleScattering, -1, 1,1);
pmanager->AddProcess(loweIon, , 2,2);
pmanager->AddProcess(loweBrem, -1,-1,3);
} else if (particleName == "e+") {
//positron
pmanager->AddProcess(new G4eIonisation, , 2,2);
pmanager->AddProcess(new G4eBremsstrahlung, -1,-1,3);
pmanager->AddProcess(new G4eplusAnnihilation, 0,-1,4); }
void BrachyPhysicsList::ConstructEM() {
theParticleIterator->reset();
while( (*theParticleIterator)() ){
G4ParticleDefinition* particle = theParticleIterator->value();
G4ProcessManager* pmanager = particle->GetProcessManager();
G4String particleName = particle->GetParticleName();
//processes
lowePhot = new G4LowEnergyPhotoElectric("LowEnPhotoElec");
loweIon = new G4LowEnergyIonisation("LowEnergyIoni");
loweBrem = new G4LowEnergyBremsstrahlung("LowEnBrem");
if (particleName == "gamma") {
//gamma
pmanager->AddDiscreteProcess(new G4LowEnergyRayleigh);
pmanager->AddDiscreteProcess(lowePhot);
pmanager->AddDiscreteProcess(new G4LowEnergyCompton);
pmanager->AddDiscreteProcess(new G4LowEnergyGammaConversion);

7. X-ray fluorescence Physics: Low Energy processes, atomic relaxation
sample
detector
beam
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"
Scattered
photons
Fe lines
GaAs lines

8. Process Registration X-ray Fluor
else if (particleName == "proton") {
//proton
pmanager->AddProcess(new G4MultipleScattering,-1,1,1);
pmanager->AddProcess(new G4hLowEnergyIonisation,-1, 2,2); }
else if ( particleName == "alpha" ) {
G4hLowEnergyIonisation* iIon = new G4hLowEnergyIonisation() ;
pmanager->AddProcess(iIon,-1,2,2);
void XrayFluoPhysicsList::ConstructEM() {
theParticleIterator->reset();
while( (*theParticleIterator)() ){
G4ParticleDefinition* particle = theParticleIterator->value();
G4ProcessManager* pmanager = particle->GetProcessManager();
G4String particleName = particle->GetParticleName();
if (particleName == "gamma") {
// gamma
pmanager->AddDiscreteProcess(new G4LowEnergyCompton);
LePeprocess = new G4LowEnergyPhotoElectric();
//LePeprocess->ActivateAuger(false);
//LePeprocess->SetCutForLowEnSecPhotons(10000 * keV);
//LePeprocess->SetCutForLowEnSecElectrons(10000 * keV);
pmanager->AddDiscreteProcess(LePeprocess);
pmanager->AddDiscreteProcess(new G4LowEnergyRayleigh); }
else if (particleName == "e-") {
//electron
pmanager->AddProcess(new G4MultipleScattering,-1, 1,1);
LeIoprocess = new G4LowEnergyIonisation();
//LeIoprocess->ActivateAuger(false);
//LeIoprocess->SetCutForLowEnSecPhotons(10000 keV);
//LeIoprocess->SetCutForLowEnSecElectrons(10000 keV);
pmanager->AddProcess(LeIoprocess, -1, 2, 2);
LeBrprocess = new G4LowEnergyBremsstrahlung();
pmanager->AddProcess(LeBrprocess, -1, -1, 3);
} else if (particleName == "e+") {
//positron
pmanager->AddProcess(new G4eIonisation, , 2,2);
pmanager->AddProcess(new G4eBremsstrahlung, -1,-1,3);
pmanager->AddProcess(new G4eplusAnnihilation, 0,-1,4); }

9. Underground physics mirror LXe GXe source PMT
// 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:
#include "G4hLowEnergyIonisation.hh"
#include "G4EnergyLossTables.hh"
//muon:
#include "G4MuIonisation.hh"
#include "G4MuBremsstrahlung.hh"
#include "G4MuPairProduction.hh"
#include "G4MuonMinusCaptureAtRest.hh"
LXe
GXe
PMT
mirror
source

10. Process Creation - DMX void DMXPhysicsList::ConstructEM() {
// 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 = 250*eV;
lowePhot->SetCutForLowEnSecPhotons(fluorcut);
loweIon ->SetCutForLowEnSecPhotons(fluorcut);
loweBrem->SetCutForLowEnSecPhotons(fluorcut);

11. Hadron Ionisation – Choosing a model
G4hLowEnergyIonisation* ahadronLowEIon = new G4hLowEnergyIonisation();
ahadronLowEIon->SetNuclearStoppingPowerModel("ICRU_R49") ;
ahadronLowEIon->SetNuclearStoppingOn() ;
// ahadronLowEIon->SetElectronicStoppingPowerModel
// (G4GenericIon::GenericIonDefinition(), "ICRU_R49p") ;
// (G4Proton::ProtonDefinition(), "ICRU_R49p") ;
// Switch off the Barkas and Bloch corrections
ahadronLowEIon->SetBarkasOff();
// Switch off hadron-induced fluorescence (for now)
ahadronLowEIon->SetFluorescence(false);
// NOTE: the same G4hLowEnergyIonisation process is applied to all hadrons, which need not be the case!

12. Attaching Processes to Particles:
theParticleIterator->reset();
while( (*theParticleIterator)() ){
G4ParticleDefinition* particle = theParticleIterator->value();
G4ProcessManager* pmanager = particle->GetProcessManager();
G4String particleName = particle->GetParticleName();
G4String particleType = particle->GetParticleType();
G4double particleCharge = particle->GetPDGCharge();
// gamma
if (particleName == "gamma") {
pmanager->AddDiscreteProcess(new G4LowEnergyRayleigh());
pmanager->AddDiscreteProcess(lowePhot);
pmanager->AddDiscreteProcess(new G4LowEnergyCompton());
pmanager->AddDiscreteProcess(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->AddProcess(aMultipleScattering, , 1, 1);
pmanager->AddProcess(loweIon, , 2, 2);
pmanager->AddProcess(loweBrem, ,-1, 3); }
// positron
else if (particleName == "e+")
pmanager->AddProcess(new G4eIonisation(), , 2, 2);
pmanager->AddProcess(new G4eBremsstrahlung(), -1,-1, 3);
pmanager->AddProcess(new G4eplusAnnihilation(), 0,-1, 4);

14. Attaching Processes to Particles:
// muons
else if( particleName == "mu+" ||
particleName == "mu-" ) {
pmanager->AddProcess(aMultipleScattering, , 1, 1);
pmanager->AddProcess(new G4MuIonisation(), , 2, 2);
pmanager->AddProcess(new G4MuBremsstrahlung(), -1,-1, 3);
pmanager->AddProcess(new G4MuPairProduction(), -1,-1, 4);
if( particleName == "mu-" )
pmanager->AddProcess(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->AddProcess(aMultipleScattering, -1, 1, 1);
pmanager->AddProcess(ahadronLowEIon, , 2, 2); }
// all other charged particles except geantino
else if ((!particle->IsShortLived()) &&
(particleCharge != 0.0) &&
(particleName != "chargedgeantino"))

16. Setting Energy Cuts: //special for low energy physics
G4double lowlimit=250*eV;
G4Gamma ::SetEnergyRange(lowlimit,100*GeV);
G4Electron::SetEnergyRange(lowlimit,100*GeV);
G4Positron::SetEnergyRange(lowlimit,100*GeV);

17. 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 Simulation of Test-Mass Charging in the LISA Mission
Very long base-line: 1 million km
Very high precision: < 1nm – 1pm (!)

23. Physics List EM processes (LowE) Electrons, Gammas, etc
Atomic de-excitation
Hadrons
(no hFluorescence)
Secondaries
Cuts: (250 eV), 1mm - 5mm
Kill e- outside caging

24. G4 result: 58 +e/s Results I Charging rate 2 days in parallel !!!
45 s exposure
~ 10,000,000 events
1 charging event
~ 2,000 events
~ 40,000 events/day/CPU
2 days in
parallel !!!
Charging rate
G4 result: 58 +e/s
(G3 result: 11 +e/s)
52 +e/s
6 +e/s

25. Results II
Cuts
(~0.1 um)
250 eV
52 +e/s
1 um
8.77 keV
41 +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!

26. Other Users – SPACE and Cosmic Ray
GLAST
AGILE
Cosmic rays,
jovian electrons
Solar X-rays, e, p
Courtesy SOHO EIT
GLAST

27. The Future… Foreseen Development plan 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

28. Conclusions To learn more…………: http://www.ge.infn.it/geant4/lowE
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.
To learn more…………:
Geant4 Physics Reference Manual
Application Developer Guide