Difference between revisions of "Start Counter Simulations"

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(Optical Surface)
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* Variation of sigma_alpha with '''ground''' finish: [https://pion.fiu.edu/~puneetk/startcounter/pics/bentbar_12x12_atten_sigalpha_ground_1.png]
 
* Variation of sigma_alpha with '''ground''' finish: [https://pion.fiu.edu/~puneetk/startcounter/pics/bentbar_12x12_atten_sigalpha_ground_1.png]
 
* Variation of lobe reflectivity with '''ground''' finish: [https://pion.fiu.edu/~puneetk/startcounter/pics/bentbar_12x12_atten_lobe_ground_1.png]
 
* Variation of lobe reflectivity with '''ground''' finish: [https://pion.fiu.edu/~puneetk/startcounter/pics/bentbar_12x12_atten_lobe_ground_1.png]
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== Optical Tests ==
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We want to implement different optical surface properties to different edges of the scintillator because the scintillators we have obtained from McNeal  indicate edges have different finishing under the microscope. The flat face have better polishing but the thin edges have groove-like polishing. We want to implement this behavior in Geant4 and study it.
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* First test with a straight 15x30x600mm straight '''scintillator''' (Blue) surrounded by a large '''Hall''' filled with Air (Mother volume)
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* Second place a '''thin bar''' (magenta), filled with Air to match the properties of '''Hall''', running along one of the edges of the '''scintillator'''
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* Define an G4LogicalBorderSurface between the '''scintillator''' and the '''thin bar''' that have an optical surface property that is different than that between '''scintillator''' and '''Hall'''

Revision as of 15:54, 20 July 2012

Geant4 Simulations

Geometry and Setup

  • Scintillator: Imported AutoCAD drawing into GEANT4 using CADMESH utility
  • SiPM: 12x12x10 mm volume
  • Surrounded by Air
  • Spacing between scintillator and SiPM: 0.1 mm
  • Generated 10K optical photons at every 2.5 cm spacing inside the scintillator (-300, 300) mm or (0, 60) cm

Material Properties

  • Scintillator: ELJAN 212 material composition properties
    • Density: 1.023 g/cm3
    • Scintillation yield: 10000 photons/MeV
    • Optical photon energy range: 0.5 eV - 3.76 eV
    • Index of refraction: 1.58
    • Absorption length: 400cm (not correct!)
  • SiPM: Silicon
    • Efficiency: 100%
    • Used just to track optical photon hits

Optical Surface

  • The actual scintillators under microscope: [4] [5]
  • An optical surface between air and scintillator is set
  • Properties of optical surface are defined by
    • Material of surfaces: dielectric_dielectric
    • Physics model: unified Levin and Moisan, 1996
    • Transmission efficiency and reflection
    • Finish of the surface: polished or ground
      • polished: Fresnel reflection, Total Internal Reflection, Fresnel Refraction
      • ground: Spike reflection, lobe reflection, backscatter, Lambertian reflection, Fresnel refraction
Spike reflection: the photon is reflected like a perfect mirror or about the average surface normal
Lambertian reflection: the photon is reflected with a Lambertian distribution
Back scatter: the photon is reflected in the direction of incidence
Lobe reflection: based on the orientation of the micro-facet on the surface. 
    The sigma_alpha parameter defines the standard deviation of the distribution of the micro-facets orientation
  • Measurement of Scintillator 1 (at FIU): [6]
  • Variation of transmission efficiency with polished finish: [7]
  • Variation of sigma_alpha with ground finish: [8]
  • Variation of lobe reflectivity with ground finish: [9]


Optical Tests

We want to implement different optical surface properties to different edges of the scintillator because the scintillators we have obtained from McNeal indicate edges have different finishing under the microscope. The flat face have better polishing but the thin edges have groove-like polishing. We want to implement this behavior in Geant4 and study it.

  • First test with a straight 15x30x600mm straight scintillator (Blue) surrounded by a large Hall filled with Air (Mother volume)
  • Second place a thin bar (magenta), filled with Air to match the properties of Hall, running along one of the edges of the scintillator
  • Define an G4LogicalBorderSurface between the scintillator and the thin bar that have an optical surface property that is different than that between scintillator and Hall