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Simulation of NUSTAR crystals with Litrani

Litrani is a Monte Carlo program developed at CEA, Saclay for simulating the transmission of optical photons in anisotropic media. This presentation discusses preliminary results, including light yield, interface with GEANT4 simulations, and the simulation of NUSTAR crystals.

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Simulation of NUSTAR crystals with Litrani

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  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

  2. 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/gentit/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

  3. 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

  4. Material definition (2) • Time profile • Wavelength profile

  5. 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 Requirements for the simulation Readout (PMT, APD) y g x z w CsI(Tl) h l

  6. PIN – CsI(Tl)#2 y x z 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

  7. PMT PIN 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

  8. 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)

  9. 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, 66mm) • Refine the models: • APD response • Scintillator response • Consequences of ageing • Detector noise

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