Transcript Silicon drift detectors coupled to CsI(Tl) scintillators

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
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Wide Field Monitor
What may be requested to it?
Primarily:
Sensitivity (to transient events)
FOV coverage
Angular resolution
Extended energy range
Eventually:
Coded mask system
coupled to a
“position sensitive”
detector plane
Energy resolution
Time resolution
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Building blocks for the detector plane
Why scintillators ?
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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
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AGILE MiniCalorimeter detector elements
CsI(Tl) 1.5 x 2.3 x 37.5 cm in size
Volume: 1.3 102 cm3
array with CsI(Tl) elements
0.03 x 0.03 x 2cm in size
Volume: 2 10-4 cm3
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Building blocks for the detector plane
Why Silicon Photodetectors?
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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..)
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The Silicon Drift Chamber
The collecting anode capacitance is very small (> 0.1 pF) and
independent from the device area

very low noise readout
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SDC as direct X detector
241Am
Range: > .6  30 keV
active area
10 mm2
Si thickness
300 mm
JFET
embedded
E threshold
0.6 keV
E resolution @ 20°C
(0.5 msec sh. time)
5% FWHM @5.9 keV
0.9% FWHM @ 60 keV
Noise (ENC)
45 e- rms @ 20°C
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55Fe
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SDC coupled to a scintillator
Range: 15  1000 keV
crystal
CsI(Tl)
light yield
25 - 38 e-/keV
E threshold
< 16 keV
efficiency
(1 cm crystal)
80% @ 200 keV
25% @ 1 MeV
energy resolution
4.8% FWHM @ 662 keV
at room temperature
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137Cs
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Prototype SDC-PD: as they look like
studies on
1.2 cm
Bonding on ceramic support
Passivation SDC
Top view
Materials for optical coupling
SDC area ~10 mm2
Bottom view
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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:
–
SDD
scintillator
g
X
Si
CsI(Tl)
Low energy threshold (~2 keV)
–
Extended energy range (related to
crystal thickness)
–
Excellent energy resolution
Direct
detection in Si
Scintillation
light detection
M. Marisaldi, IEEE Trans. NS Vol 51, No 4, 2004, p. 1916
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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
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In CsI: r = 0.54
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Pulse Shape Discrimination (PSD)
Factor of merito M
100% PSD possible when M > 1.5
r
M
 Si   CsI
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
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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
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How much to cool?
Threshold in CsI
• cooling at 10 °C is enough to fill the efficiency gap between Silicon and the crystal
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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
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Wide field monitor design
Example of a monitor that can be realised
with already available components:
Coded mask instrument
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• 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 q = 18’
• point source localisation q = 3.5’
• number of pixels: 12000.
at 5s
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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.
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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
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Technical challenge: number of pixel
•
X and g with exploding number of channels
•
PICsIT-INTEGRAL (2002):
TRACKER AGILE (2006):
GLAST even more
4.096 ch
46.000 ch

•
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 analoguedigital technology is mandatory.
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ASIC for electronic read-out
HERITAGE: ICARUS ASIC
16 channels each one with:
charge-preamp,
discriminator
Multiplexer
power:
8 mW/ch
noise:
950 e- rms
shaping amplifier
peak & hold
command logic
For PIN PD e CsI(Tl)
256 chip on PICsIT-INTEGRAL
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ASIC for SDC
RUA ASIC
ICARUS footprint
1 prototype built
16 channe/ASIC:
each channel with:
I/F to SDD
discriminator
Multiplexer
power:
8 mW/ch
noise:
60 e- rms
shaping amplifier
peak & hold
command logic
For SDC:
2 possibilities:
8 ch for X-ray detection
8 ch for CsI(Tl)
I/F to detector
discriminator
ADC
shaping amplifier
peak & hold
I/F
Noise with SDC: > 50 e- rms
Can be used for many
different detectors
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RUA prototype
Chip Area
Channel Area
Digital output
# of programmable reg.
13.7 mm2
3.3 mm2
10 bits
47
RUA layout
Programmable parameters
Amp. gain
Peaking time
Pole-zero correction
Polarity
Fine gain
Threshold
Rise time protection
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1, 2, 5, 10
0.5, 1, 3, 6 µs
0.1, 0.2, 0.5, 1, 2 ms
+/1 ÷ 2 with 10-bit
1.5 V ÷ 1.7 V with 8-bit
1, 2, 5, 8, 10 µs
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RUA
Shaper programmability
Variuos peaking time programmable with RUA
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Possible improvement: new materials
New Lanthanum composites recently available
LaBr3(Ce)
Density
g/cm3
5.29
Decay time
ns
26
LaCl3(Ce)
3.79
28
Light yield
Light yield vs NaI(Tl)
Wavelength of max em
Hygroscopic
ph/keV
%
nm
63
130
350
yes
49
70-90
380
yes
Res.FWHM @661 keV
(with PMT)
%
2.8
3.8
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CsI(Tl)
4.51
600 - 3400
50
45
560
no
8
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New materials: can be used with SDC?
Yes
if a wavelength shifter is used between crystal and PD
e (%)
Res @ 661 keV
50
1.7
30
2.3
10
4.6
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
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