Simulation of NUSTAR crystals with Litrani

1
Simulation of NUSTAR crystals with Litrani

• Presentation of Litrani simulation of optical
  photons
• Preliminary results
• Light yield
• Interface with GEANT4 simulations

Meeting at IPNO, Orsay, France
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What is Litrani ?
LITRANI stands for LIght TRansmission in
ANIsotropic media.

• General purpose Monte-Carlo program to simulate
  the propagation of optical photons
• ROOT library (Version 3.3, with ROOT 4.04/02
  Windows, Linux with gcc 3.2)
• Developped at CEA, Saclay, France for GLAST and
  the CMS calorimeter (http//gentit.home.cern.ch/ge
  ntit/litrani)
• Classes and data library from measured materials
  
• Scintillators PbWO4, CsI(Tl)
• Revetments Tyvek, VM2000
• Detectors PMT (XP2020), APD
• Surface state depolished, thin slice of air
• Easy to extend the library

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Material definition (1)

• All properties parametrized as a function of the
  wavelength
• Crystal geometry and parameters
• Light emission
• Absorption length
• Index of refraction
• Revetment
• Diffusion and reflection
• absorption
• Glue
• absorption length
• reflectivity
• PMT definition
• Glass window refraction, absorption length and
  reflectivity
• Photocathode surface and reflectivity
• Quantum efficiency

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Material definition (2)

• Time profile
• Wavelength profile

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Requirements for the simulation

• Crystal CsI(Tl) (Saint Gobain), wrapped with
  reflector (VM2000, Tyveck?)
• Geometry
• A 22 (h) 22(w) 200(l) mm
• B 22 (h) 44(w) 200(l) mm
• C 22 (h) 66(w) 200(l) mm
• Particles g (500 keV 30 MeV)
• Tests with (511 and) 662 keV
• Readout (on face w h)
• PMT (Photonis 19 mm Ø, 17 mm PK Ø)
• APD (square, 10 mm)
• Goals
• Optimize the readout
• Particle localization
• Questions
• Energy resolution
• Homogeneity
• Time response

w
CsI(Tl)
h
l
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Simulation results yield vs position

• Yield over a quarter of the volume (for 50 000
  photons emitted), sum over 5 µs
• Relative RMS of the yield distribution
  contribution of the collection to the resolution
  / dispersion dominated by the statistics
• Optimistic hypotheses on the PIN, dependence on
  the crystal doping

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Simulation analysis with CsI(Tl) 1

• Wavelength statistics over the whole simulated
  volume
• Result dependent on the wavelength distribution
  width chosen for the simulation
• Histograms can also be available for a voxel

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Simulated tracks in a single crystal

• Input ROOT file from GEANT4 simulations by T.
  Zerguerras
• Current algorithm
• Generate a random yield values from the
  distribution calculated on the volume
• Calculate the number of photons received from
  those yields and the deposited energy
• Simulation with the PMT and PIN diode (with
  CsI(Tl) 1)

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Conclusion

• The RDD group can carry out a full simulation of
  the crystal response resolution and time
  response
• Next steps
• Comparison of simulations with measurements
  (source different crystals 22, 44, 66 mm)
• Refine the models
• APD response
• Scintillator response
• Consequences of ageing
• Detector noise