Nustar/crystal simulations

2006-10-03 genolini@ipno.in2p3.fr B. Genolini

• 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: (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

w

h

l

CsI(Tl)

Readout(PMT, APD)

z

y

x

Injected with a source

Nustar/crystal simulations

2006-10-03 genolini@ipno.in2p3.fr B. Genolini

• 222222 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

Injection with a source

Simulations by T. Zerguerras: 10,000 injected

Nustar/crystal simulations

2006-10-03 genolini@ipno.in2p3.fr B. Genolini

Crystal non linearity + non uniformity

• 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

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

2.7 %

Nustar/crystal simulations

2006-10-03 genolini@ipno.in2p3.fr B. Genolini

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)

z

y

x

• Yield over a quarter of the volume (for 20 000 photons emitted), sum over 5 µs

Nustar/crystal simulations

2006-10-03 genolini@ipno.in2p3.fr B. Genolini

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 %

22×22×220 mm 22×44×200 mm 22×66×200 mm

Nustar/crystal simulations

2006-10-03 genolini@ipno.in2p3.fr B. Genolini

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

Nustar/crystal simulations

2006-10-03 genolini@ipno.in2p3.fr B. Genolini

2222220 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 at

660 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