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Based on work made at: IASF - INAF Sezione di Bologna IASF - INAF Sezione di Milano IASF - INAF Sezione di Roma ENEA FIS Bologna Politecnico di Milano, Dpt. Elettronica e Inf. Università di Pavia, Dpt. Ing. Elettronica PNSensor GmbH München Wide Field MonitorProspect for use of Silicon and scintillator detectors
Primarily: Sensitivity (to transient events) FOV coverage Angular resolution Extended energy range Eventually: Energy resolution Time resolution Wide Field MonitorWhat may be requested to it? Coded mask system coupled to a “position sensitive” detector plane
Why scintillators ? Many materials available with various characteristic of density, velocity, light output. May be shaped in many forms and size Consolidated technology New appealing materials with improved spectroscopic capabilities Can directly compete in performances with solid state detector Building blocks for the detector plane
array with CsI(Tl) elements 0.03 x 0.03 x 2cm in size Volume: 2 10-4 cm3 AGILE MiniCalorimeter detector elements CsI(Tl) 1.5 x 2.3 x 37.5 cm in size Volume: 1.3 102 cm3
Why Silicon Photodetectors? High QE (90%) for visible light Si technology allows many device design focussed on low noise level (SDC-PD), or speed (avalanche or PIN PD) Can be used as detector for visible photon or directly for low energy X-rays Naturally suited for ‘array architectures’ (small, ligth, rugged, etc..) Building blocks for the detector plane
The Silicon Drift Chamber The collecting anode capacitance is very small (> 0.1 pF) and independent from the device area very low noise readout
Range: > .6 30 keV active area 10 mm2 Si thickness 300 mm JFET embedded E threshold 0.6 keV E resolution @ 20°C 5% FWHM @5.9 keV (0.5 msec sh. time) 0.9% FWHM @ 60 keV Noise (ENC) 45 e- rms @ 20°C SDC as direct X detector 241Am 55Fe
Range: 15 1000 keV crystal CsI(Tl) light yield 25 - 38 e-/keV E threshold < 16 keV efficiency 80% @ 200 keV (1 cm crystal) 25% @ 1 MeV energy resolution 4.8% FWHM @ 662 keV at room temperature SDC coupled to a scintillator 137Cs
studies on Bonding on ceramic support Passivation SDC Materials for optical coupling SDC area ~10 mm2 Prototype SDC-PD: as they look like 1.2 cm Top view Bottom view
SDD scintillator g X Si CsI(Tl) Direct detection in Si Scintillation light detection One unique detector for extended energy range X-ray interacts in Si delivering a fast charge pulse : (< 10 ns) g-ray pass throug Si and interact in CsI(Tl) delivering a slow pulse: (few ms) The identification of the interaction type will be done with a Pulse Shape Discrimination (PSD) technique Main Characteristics: • Low energy threshold (~2 keV) • Extended energy range (related to crystal thickness) • Excellent energy resolution M. Marisaldi, IEEE Trans. NS Vol 51, No 4, 2004, p. 1916
Fast vs slow component • In the plane fast-slow channel the two operation modes (X,g ) are well defined in two row with different r = Channelfast / Channelslow Am-241 In Si: r = 0.92 In CsI: r = 0.54
Pulse Shape Discrimination (PSD) Factor of merito M 100% PSD possible when M > 1.5 6.7 - 17 keV in Si 70 - 180 keV in CsI • 100% PSD for E>3.6 keV in Si and E>35 keV in CsI • PSD still possibile per E>1.5 keV in Si and E>16 keV in CsI • lower noise and greater light yield –––> lower PSD limit
PSD limit vs Temperature M=1.5 25 °C: 4.5 keV in Si, 46 keV in CsI -20 °C: 1.0 keV in Si, 7 keV in CsI 10 °C: 2.0 keV in Si, 18 keV in CsI 0 °C: 1.7 keV in Si, 15 keV in CsI
How much to cool? Threshold in CsI • cooling at 10 °C is enough to fill the efficiency gap between Silicon and the crystal
Mixed interactions With PSD it is possible to discriminate mixed interactions in Si and CsI 26 keV in Si: r=0.92 60 keV in CsI + I KL and Cs KL X-rays in Si: r~0.87 Mixed events can be rejected,or corrected
Wide field monitor design • Example of a monitor that can be realised with already available components: • pixel size d=3.6 mm • detector size D=400 mm • mask size M=800 mm • mask-destector focal length l=1 m • fully coded FOV = 43.6° • FWHM = 77.3° (1.4 sr) • angolar resolutionq = 18’ • point source localisation Dq = 3.5’ at 5s • number of pixels: 12000. Coded mask instrument
Gamma flash sensitivity Faintest detectable burst (1-1000 keV), from Band, D., (2003) ApJ 588, 945 Integral flux for 3 different GRB (a, b, Ep spectral parameters, Band D. et al., 1993, ApJ 413, 281). Solid :a=-1,b=-2. Dashed:a=-0.5,b=-2. Dot-dashed:a=-1,b=-3. Trigger range 1.5 - 40 keV Trigger range 20 - 1000 keV SDC/scintillator detectors cover, in an unique instrument an energy band over 3 order of magnitude. The spectroscopic capabilities of SDC allow a continuing monitoring of a detected burst during the pointing of the narrow field instruments.
Transient studies:A monitor working on an extended Energy range can be used to study strong absorbed sources like that one found by INTEGRAL. Monitoring of known sources:If the monitor FOV is large enough it can be possible the monitoring of the timing and spectral variability of known sources GRB studies:A wide energy band can be a benefit on the studies of GRB Cosmic Background:Like SAX-PDS a monitor with good sensitivity can be used for CB studies Further scientific revenues from a Wide Field Monitor with an extended energy range
Technical challenge: number of pixel • X and g with exploding number of channels • PICsIT-INTEGRAL (2002): 4.096 ch • TRACKER AGILE (2006): 46.000 ch • GLAST even more • • Read-out electronic chain using very large integration techniques with: • Whole analogue chain suitable for spectroscopy • Many embedded logical function to ‘harmonize’ the behaviour of different detector in an unique array • Low power consumption, miniaturisation, Latch-up e SEU immunity • • Use of Application Specific Integrated Circuits (ASIC) with mixed analogue-digital technology is mandatory.
ASIC for electronic read-out HERITAGE: ICARUS ASIC 16 channels each one with: charge-preamp, shaping amplifier discriminator peak & hold Multiplexer command logic power: 8 mW/ch noise: 950 e- rms For PIN PD e CsI(Tl) 256 chip on PICsIT-INTEGRAL ASIC for SDC ICARUS footprint 16 channe/ASIC: I/F to SDD shaping amplifier discriminator peak & hold Multiplexer command logic power: 8 mW/ch noise: 60 e- rms For SDC: 2 possibilities: 8 ch for X-ray detection 8 ch for CsI(Tl) RUA ASIC 1 prototype built each channel with: I/F to detector shaping amplifier discriminator peak & hold ADCI/F Noise with SDC: > 50 e- rms Can be used for many different detectors
RUA prototype Chip Area 13.7 mm2 Channel Area 3.3 mm2 Digital output 10 bits # of programmable reg. 47 RUA layout Programmable parameters Amp. gain 1, 2, 5, 10 Peaking time 0.5, 1, 3, 6 µs Pole-zero correction 0.1, 0.2, 0.5, 1, 2 ms Polarity + / - Fine gain 1 ÷ 2 with 10-bit Threshold 1.5 V ÷ 1.7 V with 8-bit Rise time protection 1, 2, 5, 8, 10 µs
RUA Shaper programmability Variuos peaking time programmable with RUA
New Lanthanum composites recently available LaBr3(Ce) LaCl3(Ce) CsI(Tl) Density g/cm3 5.29 3.79 4.51 Decay time ns 26 28 600 - 3400 Light yield ph/keV 63 49 50 Light yield vs NaI(Tl) % 130 70-90 45 Wavelength of max em nm 350 380 560 Hygroscopic yes yes no Res.FWHM @661 keV % 2.8 3.8 8 (with PMT) Possible improvement: new materials
Yes if a wavelength shifter is used between crystal and PD Estimated Energy resolution FWHM @ 661 keV vs efficiency of light collection in the SDC (noise SDC considered 50 e- rms) PSD for use of both Si and crystal at the same time may be still possible:need To Be Investigated New materials: can be used with SDC?