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Roma Jan.2006 WHIM and mission opportunities
Wide Field Monitor
Prospect for use of Silicon and scintillator detectors
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
Roma Jan.2006 WHIM and mission opportunities
Wide Field Monitor
What may be requested to it?
Primarily:Sensitivity (to transient events)
FOV coverage
Angular resolution
Extended energy range
Eventually:Energy resolution
Time resolution
Coded mask system
coupled to a
“position sensitive”
detector plane
Roma Jan.2006 WHIM and mission opportunities
Building blocks for the detector plane
Why scintillators ?
א Many materials available with various characteristic of
density, velocity, light output.א May be shaped in many forms and sizeא Consolidated technologyא New appealing materials with improved spectroscopic New appealing materials with improved spectroscopic
capabilitiescapabilities
Can directly compete in performances with solid state detector
Roma Jan.2006 WHIM and mission opportunities
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
Roma Jan.2006 WHIM and mission opportunities
Building blocks for the detector plane
Why Silicon Photodetectors?
High QE (90%) for visible lightك Si technology allows many device design focussed on lowك
noise level (SDC-PD), or speed (avalanche or PIN PD) Can be used as detector for visible photon or directly for lowك
energy X-rays ,Naturally suited for ‘array architectures’ (small, ligth, ruggedك
etc..)
Roma Jan.2006 WHIM and mission opportunities
The Silicon Drift Chamber
The collecting anode capacitance is very small (> 0.1 pF) and
independent from the device area
very low noise readout
Roma Jan.2006 WHIM and mission opportunities
SDC as direct X detector
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 sec sh. time) 0.9% FWHM @ 60 keV
Noise (ENC) 45 e- rms @ 20°C
241Am
55Fe
Roma Jan.2006 WHIM and mission opportunities
SDC coupled to a scintillator
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 keVat room temperature 137Cs
Roma Jan.2006 WHIM and mission opportunities
Prototype SDC-PD: as they look like
studies on
Bonding on ceramic support
Passivation SDC
Materials for optical coupling
SDC area ~10 mm2
Top view
Bottom view
1.2 cm
Roma Jan.2006 WHIM and mission opportunities
One unique detector for extended energy range
X-ray interacts in Si delivering a fast charge pulse : (< 10 ns)
-ray pass throug Si and interact in CsI(Tl) delivering a slow pulse: (few s)
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
Si CsI(Tl)
X
Direct detection in Si
Scintillationlight detection
SDD scintillator
Roma Jan.2006 WHIM and mission opportunities
Fast vs slow component
Am-241
• In the plane fast-slow channel the two operation modes (X,) are well defined in two row with different r = Channelfast / Channelslow
In Si: r = 0.92 In CsI: r = 0.54
Roma Jan.2006 WHIM and mission opportunities
Pulse Shape Discrimination (PSD)
CsISi
rM
Factor of merito M100% PSD possible when M >
1.5
• 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
6.7 - 17 keV in Si
70 - 180 keV in CsI
Roma Jan.2006 WHIM and mission opportunities
PSD limit vs Temperature
25 °C: 4.5 keV in Si, 46 keV in CsI
M=1.5
10 °C: 2.0 keV in Si, 18 keV in CsI0 °C: 1.7 keV in Si, 15 keV in CsI
-20 °C: 1.0 keV in Si, 7 keV in CsI
Roma Jan.2006 WHIM and mission opportunities
How much to cool?
Threshold in CsI
•cooling at 10 °C is enough to fill the efficiency gap between Silicon and the crystal
Roma Jan.2006 WHIM and mission opportunities
Mixed interactions
With PSD it is possible to discriminate mixed interactions in Si and CsI
Mixed events can be rejected,or corrected
60 keV in CsI + I KL and Cs KL X-rays in Si: r~0.87
26 keV in Si:r=0.92
Roma Jan.2006 WHIM and mission opportunities
Wide field monitor design
Coded mask instrument
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 resolution = 18’• point source localisation = 3.5’ at 5• number of pixels: 12000.
Roma Jan.2006 WHIM and mission opportunities
Gamma flash sensitivity
Integral flux for 3 different GRB (, , Ep spectral parameters, Band D. et al., 1993, ApJ 413, 281).
Solid : =-1, =-2.
Dashed: =-0.5, =-2.
Dot-dashed: =-1, =-3.
Faintest detectable burst (1-1000 keV), from Band, D., (2003) ApJ 588, 945
Trigger range 20 - 1000 keVTrigger range 1.5 - 40 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.
Roma Jan.2006 WHIM and mission opportunities
Further scientific revenues from a Wide Field Monitor with an extended energy range
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
Roma Jan.2006 WHIM and mission opportunities
Technical challenge: number of pixel
• X and with exploding number of channels
• PICsIT-INTEGRAL (2002): 4.096 chTRACKER AGILE (2006): 46.000 chGLAST 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.
Roma Jan.2006 WHIM and mission opportunities
HERITAGE: ICARUS ASIC
16 channels each one with:charge-preamp, shaping amplifierdiscriminator peak & hold Multiplexer command logicpower: 8 mW/chnoise: 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 amplifierdiscriminator peak & hold Multiplexer command logicpower: 8 mW/chnoise: 60 e- rms
For SDC:2 possibilities:8 ch for X-ray detection8 ch for CsI(Tl)
RUA ASIC
1 prototype built
each channel with:I/F to detector shaping amplifierdiscriminator peak & hold ADC I/F
Noise with SDC: > 50 e- rms
Can be used for many different detectors
ASIC for electronic read-out
Roma Jan.2006 WHIM and mission opportunities
RUA prototype
RUA layout
Chip Area 13.7 mm2
Channel Area 3.3 mm2
Digital output 10 bits
# of programmable reg. 47
Programmable parametersAmp. 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
Roma Jan.2006 WHIM and mission opportunities
RUA Shaper programmability
Variuos peaking time programmable with RUA
Roma Jan.2006 WHIM and mission opportunities
Possible improvement: new materials
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)
Roma Jan.2006 WHIM and mission opportunities
New materials: can be used with SDC?
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
(%) Res @ 661 keV
50 1.7
30 2.3
10 4.6