Simulation of optical processes in GEANT4

1
Simulation of optical processesin GEANT4

• Ralph Dollan
• DESY - ZEUTHEN

2
Outline

• First part
• Results of experiments to measure the lightyield
  of two different material samples
• Second part
• Simulations of the Photontransport in
  scintillator/leadglass samples and
  wavelenghtshifting fibers with GEANT4

3
Longitudinal Segmentation

• Crystal cutted into segments in depth
• Optical isolated fibers
• Readout with photodetectors

• Material
• radiationhard
• dense
• high lightyield

• Lightyield reduction due to fiber readout ?
• Crosstalk ?

4
BICRON BCF-91A - Fibers

• BCF-91A
• ?(max. emission) 494 nm
• -gt QE(PMT-XP1911) 13 2

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Experiment
Cosmic - Teleskop
µ-
Absorber
Discriminator
PMT - Signals
Triggerlogic
ADC
TDC
File
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Direct readout vs. fiber readout (BC-408)
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Experimental - Results
Plastic Scintillator
Leadglass
Direct readout (QEPMT 25 1 )
Photoelectrons 390 50 p.e. / µ
Lightyield 1560 260 photons / µ
Direct readout (QEPMT 15 2 )
Photoelectrons 18.2 2.2 p.e. / µ
Lightyield 120 30 photons / µ
Fiber readout (QEPMT 13 2 )
Photoelectrons 2.4 0.5 p.e. / µ
Lightyield 19 7 photons / µ
Fiber readout (QEPMT 13 2 )
Photoelectrons 27 4 p.e. / µ
Lightyield 210 60 photons / µ
Lightyield reduced to 14 4
Lightyield reduced to 16 7
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Simulation - Motivation

• To simulate the behavior of Scintillator-samples,
  optical processes provided by GEANT4
• have to be understood
• Scintillation
• Cerenkov radiation
• Transport of optical photons in the
• medium
• Reflection
• Scattering
• photons at material boundaries
• Absorption
• Reemission
• wavelength shifting

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Relevant processes for optical photons
Process Geant4 source
Cerenkov processes/electromagnetic/xray -gt G4Cerenkov
Scintillation processes/electromagnetic/xray -gt G4Scintillation
OpBoundary processes/optical -gt G4OpBoundary
OpAbsorption processes/optical -gt G4OpAbsorption
OpRayleigh processes/optical -gt G4OpRayleigh
OpWLS processes/optical -gt G4OpWLS since GEANT4 6.0
(Transportation)
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Needed

• Material properties
• atomic composition of the materials used
• refractive index
• absorption length (-spectrum)
• scintillation yield (slow/fast)
• scintillation time constant (slow/fast)
• absorption-, emission-spectra of WLS-materials
• time constants of WLS-materials

• Known
• over all refractive index
• over all absorption length
• (rel. Emission-, Absorption spectrum)
• (scintillation yield)
• time constants

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Scintillation
const G4int NUMENTRIES 12 G4double
PhotonEnergyNUMENTRIES 3.44eV,
3.26eV, 3.1eV, 3.02eV, 2.95eV, 2.92eV,
2.82eV, 2.76eV, 2.7eV, 2.58eV, 2.38eV,
2.08eV G4double RINDEX_Bc408NUMENTRIES
1.58, 1.58, 1.58, 1.58, 1.58, 1.58,
1.58, 1.58, 1.58, 1.58, 1.58, 1.58
G4double ABSORPTION_Bc408NUMENTRIES
210cm, 210cm, 210cm, 210cm, 210cm,
210cm, 210cm, 210cm, 210cm, 210cm,
210cm, 210cm
G4double SCINTILLATION_Bc408NUMENTRIES
0.04, 0.07, 0.20, 0.49, 0.84, 1.00, 0.83,
0.55, 0.40, 0.17, 0.03, 0
G4MaterialPropertiesTable Bc408_mt new
G4MaterialPropertiesTable() Bc408_mt-gtAddProper
ty("RINDEX", PhotonEnergy, RINDEX_Bc408,
NUMENTRIES) Bc408_mt-gtAddProperty("ABSLENGTH",
PhotonEnergy, ABSORPTION_Bc408, NUMENTRIES)
Bc408_mt-gtAddProperty("FASTCOMPONENT",
PhotonEnergy, SCINTILLATION_Bc408, NUMENTRIES)
Bc408_mt-gtAddConstProperty("SCINTILLATIONYIELD",5
00./MeV) Bc408_mt-gtAddConstProperty("RESOLUTION
SCALE",1.0) Bc408_mt-gtAddConstProperty("FASTTIM
ECONSTANT", 1.ns) //Bc408_mt-gtAddConstProperty
("SLOWTIMECONSTANT",1.ns) Bc408_mt-gtAddConstPr
operty("YIELDRATIO",1.) Bc408-gtSetMaterialPrope
rtiesTable(Bc408_mt)
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WLS
Absorptionlength from Code Hugh Gallagers Web
Page (Tufts University), (Scintillator studies
for the MINOS-Experiment)
const G4int NUMENTRIES3 42 G4double
PhotonEnergy_WLS_ABS_Bcf91a_coreNUMENTRIES3
3.539eV, 3.477eV, 3.340eV, 3.321eV,
3.291eV, 3.214eV, 3.162eV, 3.129eV,
3.091eV, 3.086eV, 3.049eV, 3.008eV,
2.982eV, 2.958eV, 2.928eV, 2.905eV,
2.895eV, 2.890eV, 2.858eV, 2.813eV,
2.774eV, 2.765eV, 2.752eV, 2.748eV, 2.739eV,
2.735eV, 2.731eV, 2.723eV, 2.719eV,
2.698eV, 2.674eV, 2.626eV, 2.610eV,
2.583eV, 2.556eV, 2.530eV, 2.505eV,
2.480eV, 2.455eV, 2.431eV, 2.407eV,
2.384eV G4double WLS_ABSLENGTH_Bcf91a_co
reNUMENTRIES3 0.28cm, 0.28cm,
0.26cm, 0.25cm, 0.24cm, 0.21cm,
0.19cm, 0.16cm, 0.13cm, 0.13cm,
0.14cm, 0.11cm, 0.08cm, 0.05cm, 0.02cm,
0.05cm, 0.08cm, 0.10cm, 0.13cm, 0.10cm,
0.08cm, 0.07cm, 0.08cm, 0.11cm, 0.13cm,
0.16cm, 0.19cm, 0.21cm, 0.24cm, 0.27cm,
0.30cm, 2.69cm, 3.49cm, 3.99cm,
5.00cm, 11.6cm, 21.6cm, 33.1cm,
175cm, 393cm, 617cm, 794cm
const G4int NUMENTRIES2 24 G4double
PhotonEnergy_WLS_EM_Bcf91a_coreNUMENTRIES2
2.69eV, 2.67eV, 2.66eV, 2.64eV, 2.63eV,
2.61eV, 2.58eV, 2.56eV, 2.55eV, 2.53eV,
2.50eV, 2.48eV, 2.46eV, 2.45eV,
2.44eV, 2.43eV, 2.41eV, 2.37eV,
2.33eV, 2.25eV, 2.24eV, 2.19eV,
2.15eV, 2.08eV G4double
WLS_EMISSION_Bcf91a_coreNUMENTRIES2 0,
0.02, 0.09, 0.20, 0.29, 0.40, 0.59, 0.70,
0.80, 0.89, 1.00, 0.96, 0.88, 0.79, 0.69,
0.59, 0.50, 0.40, 0.31, 0.22, 0.19, 0.10,
0.06, 0
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Geometry
WLS Fiber
Scintillator sample
Air gap
Tyvek wrapping
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Frontview
Fiber diameter 1mm, Cladding thickness 3 of
core Ø Channel 1mmx1mm
Fiber core Polystyrene, n1.6
Fiber cladding Acrylic, n1.49
Optical glue Epoxy, n1.56
Scintillator Polyvinyltoluene, n1.58
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Sideview, both sides open
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Sideview, one side open
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Front view - Photons in the Fiber
Scintillation yield 5
0
0/MeV
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PMT positions
Directly attached to fiber surface
Directly attached to scintillator sample
PMT Window Ø 15 mm, thickness 2mm Short
absorptionlength -gt all photons absorbed
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Bc_direct_3a
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Bc_fiber_3a
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Bc_direct_3a_pmt
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Bc_fiber_3a_pmt
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Lg_direct
24
Lg_fiber
25
Lg_direct_pmt
26
Lg_fiber_pmt
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Simulation - Results
Plastic Scintillator
Leadglass
(exp.) Lightyield reduced to 14 4
(exp.) Lightyield reduced to 16 7
(sim.) Lightyield reduced to 8.3 - 12
(sim.) Lightyield reduced to 9.3 9.8
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Summary
This is a first look can be improved !!!

• for a first naive look nice agreement between
  exp. and
• sim. results

• For a realistic Simulation
• implementation of realistic boundary and
  surface
• conditions of the materials/samples
• exact WLS-Absorption spectrum
• good knowledge of Absorption-, Emission
  behaviour of the
• materials
• material composition data

• these simulation studies continue
• V. Drugakov gt Simulation of a block of crystals