Simulating Optical Processes Using Geant4: Scintillating Cells and WLS Fibers

1
Simulating Optical Processes Using
Geant4Scintillating Cells and WLS Fibers
2
G4OpticalPhoton

• Optical Photon
• ? gtgt atomic spacing
• define
• G4OpticalPhotonOpticalPhoton()
• No smooth transition
• G4OpticalPhoton ltgt G4Gamma
• possible to set polarization
• photon-gtSetPolarization(px, py, pz)

3
Optical Processes

• Optical Photon Production
• Cerenkov Process
• Scintillation Process
• Transition Radiation
• Processes affecting Optical Photons
• Refraction and Reflection
• Bulk Absorption
• Rayleigh Scattering

4
General Material Properties
const G4int n 9 // distribution of optical
photons produced in eV G4double ppn
2.0eV,2.2eV,2.4eV,2.6eV,2.8eV,3.0eV,3.1eV,
3.3eV,3.5eV // refraction index G4double
rindn 1.58, 1.58, 1.58, 1.58,1.58, 1.58,
1.58, 1.58,1.58 // absorption length G4double
absln 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-gtAddProperty(RI
NDEX,pp,rind,n) mpt-gtAddProperty(ABSLENGTH,pp,
absl,n) aG4Material-gtSetMaterialPropertiesTable(
mpt)
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.
6
Scintillation Code
Physics List theScintillationProcess-gtSetScintilla
tionYieldFactor(1.) theScintillationProcess-gtSetT
rackSecondariesFirst(true)
Detector Construction G4MaterialPropertiesTable
mpt new G4MaterialPropertiesTable() //
distribution of produced optical photons G4double
scintn 0.000134, 0.004432, 0.053991,
0.241971, 0.398942, 0.004432,
0.053991, 0.241971 // refers to
pp from General Material Properties mpt-gtAddProp
erty("SCINTILLATION", pp, scint, n) // define
constants mpt-gtAddConstProperty("SCINTILLATIONYIEL
D",10000./MeV) mpt-gtAddConstProperty("FASTTIMECON
STANT",1.ns) mpt-gtAddConstProperty("SLOWTIMECONS
TANT",1.ns)
7
Scintillation Parameters

• G4Scintillation Process may use ...
• SCINTILLATION
• FASTCOMPONENT
• SLOWCOMPONENT
• SCINTILLATIONYIELD
• RESOLUTIONSCALE
• FASTTIMECONSTANT
• SLOWTIMECONSTANT
• YIELDRATIO

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

9
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

10
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

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 SLOWCOMP
ONENT SCINTILLATIONYIELD RESOLUTIONSCALE
FASTTIMECONSTANT SLOWTIMECONSTANT YIELDRATIO
Boundary Finish Model Type RINDEX SPECULARLOBECONS
TANT BACKSCATTERCONSTANT REFLECTIVITY EFFICIENCY
12
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

13
Low E mu- Fired from Top
14
Very Low E mu Illustrating Reflection
15
Side View
16
Non-Isotropic Behavior
Side
Top
(Does not include boundary processes.)
17
Ideas and Plans

• hit / SD / readout scheme
• match geometry / materials of an actual cell
  setup
• gt 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

18
Sources
1. Gumplinger, Optical Photon Processes in
Geant4. http//geant4.slac.stanford.edu/User
sWorkshop/PDF/Peter/OpticalPhoton.pdf 2.
Gumplinger, Photon Readout Simulations of Plastic
Scintillator ... http//www.triumf.ca/gean
t4-03/talks/05-Friday-PM-1/04-J.Archambault/WLS.pp
t 3. Wright, Geant4 Advanced Physics Tutorial.
http//geant4.slac.stanford.edu/g4cd/Slides
/Fermilab/PhysicsTutor2.pdf 4. Geant4 Users
Guide for Application Developers 5.2 Physics.
http//geant4.web.cern.ch/geant4/G4UsersDocument
s/UsersGuides/ForApplicationDeveloper/html/Trackin
gAndPhysics/physicsProcess.html