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Simulating Optical Processes Using Geant4: Scintillating Cells and WLS Fibers

Simulating Optical Processes Using Geant4: Scintillating Cells and WLS Fibers. G4OpticalPhoton. Optical Photon: λ >> atomic spacing define: G4OpticalPhoton::OpticalPhoton() No smooth transition: G4OpticalPhoton <=|=> G4Gamma possible to set polarization:

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Simulating Optical Processes Using Geant4: Scintillating Cells and WLS Fibers

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

  2. 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. Optical Processes • 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. Scintillation Code Physics List theScintillationProcess->SetScintillationYieldFactor(1.); theScintillationProcess->SetTrackSecondariesFirst(true); Detector Construction G4MaterialPropertiesTable *mpt = new G4MaterialPropertiesTable(); // distribution of produced optical photons G4double scint[n] = {0.000134, 0.004432, 0.053991, 0.241971, 0.398942, 0.004432, 0.053991, 0.241971}; // 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. 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. 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. 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. Low E mu- Fired from Top Simulating Optical Processes Using Geant4

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

  15. Side View Simulating Optical Processes Using Geant4

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

  17. 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. Sources 1. Gumplinger, Optical Photon Processes in Geant4. [ http://geant4.slac.stanford.edu/UsersWorkshop/PDF/Peter/OpticalPhoton.pdf ] 2. Gumplinger, Photon Readout Simulations of Plastic Scintillator [...] [ http://www.triumf.ca/geant4-03/talks/05-Friday-PM-1/04-J.Archambault/WLS.ppt ] 3. Wright, Geant4 Advanced Physics Tutorial. [ http://geant4.slac.stanford.edu/g4cd/Slides/Fermilab/PhysicsTutor2.pdf ] 4. Geant4 User’s Guide for Application Developers: 5.2 Physics. [http://geant4.web.cern.ch/geant4/G4UsersDocuments/UsersGuides/ForApplicationDeveloper/html/TrackingAndPhysics/physicsProcess.html] Simulating Optical Processes Using Geant4

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