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Requirements for the simulation

Requirements for the simulation

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Requirements for the simulation

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  1. Crystal: CsI(Tl) (Saint Gobain), wrapped with reflector (VM2000, Tyveck?) Geometry: [0]: 22 (h) × 22(w) × 22(l) mm [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, 15 mm PK Ø) APD (square, 10 mm) Goals: Optimize the readout Particle localization Questions Energy resolution Homogeneity Requirements for the simulation Readout (PMT, APD) y g x z w CsI(Tl) h l g Injected with a source

  2. Injection with a source Simulations by T. Zerguerras: 10,000 g injected • 222222 mm3 crystal • Single deposit: negligible (10 events/5235) • Multiple deposit: 20426 (~4 per event) • Large spectrum of energy deposit • high sensitivity to non uniformities and non linearities

  3. Crystal non linearity + non uniformity P. Dorenbos, J. T. M. de Haas, C. W. E. van Eijk, Non-proportionality in the Scintillation Response and Energy Resolution Obtainable with Scintillation Crystals, IEEE Trans. Nucl. Sci., vol. 42, pp. 2190-2202, 1995 W. Mengesha et al., Light Yield Nonproportionality of CsI(Tl), CsI(Na, and YAP, IEEE Trans. Nucl. Sci., vol. 45, pp. 456-461, 1998 • Non linear behavior at smaller energies • Not negligible because: average energy deposit for an injection of 660 keV = 108 keV • Contribution: 2.7 % FWHM @ 660 keV=1 % non uniformity + 2,3% non linearity 15 % Ref: 660 keV 2.7 %

  4. y x z Light collection – simulation principle • Litrani (http://gentit.home.cern.ch/gentit/litrani) • Database of GLAST: VM2000, CsI(Tl) (measured) • Extend the database with Photonis and Hamamatsu data (quantum efficiencies) • Yield over a quarter of the volume (for 20 000 photons emitted), sum over 5 µs

  5. Light collection - results(Depolished scintillator, VM2000, large PMT, green extended) • PMT on the left • Efficiency along the Z axis: mean over the X-Y plane • More efficiency in the center as close to the edge: between 2 to 3% 22×66×200 mm 22×44×200 mm 22×22×220 mm

  6. Resolution calculation • Hypothesis on the crystal gain non uniformity: 1 % • In presence of electron/positron pairs, escape peaks are not taken into account for the energy resolution calculation

  7. 2222220 mm3 crystal / non polished / VM2000 / large PMT • Resolution dominated by the collection non uniformity: • Crystal non linearity + non uniformity:2.6 % FWHM • Efficiency non uniformity:< 5.5 % FWHM • Comparison with measurements at660 keV: • Simulation: 3000 photoelectrons,8 % FWHM resolution • Measurement: 5500 photoelectrons,6.7 % FWHM resolution • Explanation of differences: • The PMT used for measurements has an excellent light yield • The "depolished" surface state is difficult to reproduce in simulations PMT at z = +110 mm