1. Simulating Optical Processes Using Geant4
Simulating Optical Processes Using Geant4: Scintillating Cells and WLS Fibers
Simulating Optical Processes Using Geant4

2. Simulating Optical Processes Using Geant4
G4OpticalPhoton
Optical Photon:
λ >> atomic spacing
define:
G4OpticalPhoton::OpticalPhoton()
No smooth transition:
G4OpticalPhoton <=|=> G4Gamma
possible to set polarization:
photon->SetPolarization(px, py, pz);
Simulating Optical Processes Using Geant4

3. Simulating Optical Processes Using Geant4
Optical Photon Production
Cerenkov Process
Scintillation Process
Transition Radiation
Processes affecting Optical Photons
Refraction and Reflection
Bulk Absorption
Rayleigh Scattering
Simulating Optical Processes Using Geant4

4. General Material Properties
const G4int n = 9;
// distribution of optical photons produced in eV
G4double pp[n] = {2.0*eV,2.2*eV,2.4*eV,2.6*eV,2.8*eV,3.0*eV,3.1*eV,3.3*eV,3.5*eV};
// refraction index
G4double rind[n] = {1.58, 1.58, 1.58, 1.58,1.58, 1.58, 1.58, 1.58,1.58};
// absorption length
G4double absl[n] = {210.*cm, 210.*cm, 210.*cm, 210.*cm,
210.*cm, 210.*cm, 210.*cm, 210.*cm, 210.*cm};
// create material properties table and setup parameters “keyed” on pp
G4MaterialPropertiesTable *mpt = new G4MaterialPropertiesTable();
mpt->AddProperty(“RINDEX”,pp,rind,n);
mpt->AddProperty(“ABSLENGTH”,pp,absl,n);
aG4Material->SetMaterialPropertiesTable(mpt);
Simulating Optical Processes Using Geant4

5. Scintillation Process
number of photons generated is proportional to the energy lost during the step
emission spectrum sampled from empirical spectra
Isotropic emission
Uniform along the track segment
With random linear polarization
Emission time spectra with one exponential decay time constant *
*All points taken from Source 1.
Simulating Optical Processes Using Geant4

6. Simulating Optical Processes Using Geant4
Scintillation Code
Physics List
theScintillationProcess->SetScintillationYieldFactor(1.);
theScintillationProcess->SetTrackSecondariesFirst(true);
Detector Construction
G4MaterialPropertiesTable *mpt = new G4MaterialPropertiesTable();
// distribution of produced optical photons
G4double scint[n] = { , , , , , ,
, };
// refers to pp from “General Material Properties”
mpt->AddProperty("SCINTILLATION", pp, scint, n);
// define constants
mpt->AddConstProperty("SCINTILLATIONYIELD",10000./MeV);
mpt->AddConstProperty("FASTTIMECONSTANT",1.*ns);
mpt->AddConstProperty("SLOWTIMECONSTANT",1.*ns);
Simulating Optical Processes Using Geant4

7. Scintillation Parameters
G4Scintillation Process may use ...
SCINTILLATION
FASTCOMPONENT
SLOWCOMPONENT
SCINTILLATIONYIELD
RESOLUTIONSCALE
FASTTIMECONSTANT
SLOWTIMECONSTANT
YIELDRATIO
Simulating Optical Processes Using Geant4

8. G4BoundaryProcess and Surfaces
reflection and refraction at physical volume surfaces
GLISUR (Geant3) or UNIFIED (DETECT / TRIUMF) model
define surface:
G4LogicalBorderSurface(name, physVol1, physVol2, G4OpticalSurface)
... or G4LogicalSkinSurface
G4OpticalSurfaceType:
dielectric_metal, dielectric_dielectric
G4OpticalSurfaceFinish:
polished, polishedfrontpainted, polishedbackpainted,
ground, groundfrontpainted, groundbackpainted
no partial refraction / reflection
See Sources 1 and 4 for examples and more details
Simulating Optical Processes Using Geant4

9. Simulating Optical Processes Using Geant4
Surface Parameters
Parameters
Finish
Model
Type
RINDEX
SPECULARLOBECONSTANT
BACKSCATTERCONSTANT
REFLECTIVITY
EFFICIENCY
Possible Optical Surfaces
cell to air
cell to fiber cladding
cladding to fiber core
core / cladding to air
Simulating Optical Processes Using Geant4

10. Simulating Optical Processes Using Geant4
WLS Process
Peter Gumplinger (TRIUMF)
next Geant4 release (6.0)
absorb photons of one wavelength and emit another
inputs:
WLSABSLENGTH, WLSCOMPONENT, WLSTIME
See Source 2
Simulating Optical Processes Using Geant4

11. Optical Parameters Summary
General
PP (emission mom.)
RINDEX
ABSLENGTH
WLS
WLSABSLENGTH
WLSCOMPONENT
WLSTIME
Possible Optical Surfaces
cell to air
cell to fiber cladding
cladding to fiber core
core / cladding to air
Scintillation
SCINTILLATION
FASTCOMPONENT
SLOWCOMPONENT SCINTILLATIONYIELD RESOLUTIONSCALE FASTTIMECONSTANT
SLOWTIMECONSTANT
YIELDRATIO
Boundary
Finish
Model
Type
RINDEX
SPECULARLOBECONSTANT
BACKSCATTERCONSTANT
REFLECTIVITY
EFFICIENCY
Simulating Optical Processes Using Geant4

12. Simulating Optical Processes Using Geant4
cellsim Application
project: /k2work/jeremy/cellsim
screenshots: /k2work/jeremy/doc/cellsim
Geant4 optical processes plus WLS
Mokka 2 “base” physics
hard coded geometry:
cell : 6 x 2 x 24
fiber : r = 1 mm
material parameters
additional physics:
G4OpBuilder, G4OpWLS (PG), OpPhysics
user action / mandatory Geant4 classes
GPS
Simulating Optical Processes Using Geant4

13. Simulating Optical Processes Using Geant4
Low E mu- Fired from Top
Simulating Optical Processes Using Geant4

14. Very Low E mu+ Illustrating Reflection
Simulating Optical Processes Using Geant4

15. Simulating Optical Processes Using Geant4
Side View
Simulating Optical Processes Using Geant4

16. Non-Isotropic Behavior
Side
Top
(Does not include boundary processes.)
Simulating Optical Processes Using Geant4

17. Simulating Optical Processes Using Geant4
Ideas and Plans
hit / SD / readout scheme
match geometry / materials of an actual cell setup
> 1 cell for X-talk / multiple cell effects measurements
UI commands for specifying cell dimensions, surface properties & composition at runtime
compare with actual results from Sasha, et al
examine why not always isotropic distributions along firing axis
realistic values for material / process parameters
test acurracy of Geant4 optical model
Simulating Optical Processes Using Geant4

18. Simulating Optical Processes Using Geant4
Sources
1. Gumplinger, Optical Photon Processes in Geant4.
[ ]
2. Gumplinger, Photon Readout Simulations of Plastic Scintillator [...]
[ ]
3. Wright, Geant4 Advanced Physics Tutorial.
[ ]
4. Geant4 User’s Guide for Application Developers: 5.2 Physics.
[ ]
Simulating Optical Processes Using Geant4