Semi conductor detectors for soft gamma-ray astrophysics · Semi conductor detectors for soft...
Transcript of Semi conductor detectors for soft gamma-ray astrophysics · Semi conductor detectors for soft...
Semi conductor detectors Semi conductor detectors for soft gammafor soft gamma--ray astrophysicsray astrophysics
François LebrunFrançois LebrunAPC (UMR 7164), APC (UMR 7164), CEACEA--SaclaySaclay
ISGRI PIISGRI PI IWORID 2005 Grenoble
HighHigh--energy astronomy energy astronomy specific telescopesspecific telescopes
XX--rays and gamma raysrays and gamma rays
radio, IR, visible, UVradio, IR, visible, UV
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Atmospheric absorption Atmospheric absorption space experimentsspace experimentsA
tmos
pher
icO
paci
ty
Wavelength
γ-rays
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internal background internal background minimization of the minimization of the detector and surrounding material massdetector and surrounding material mass
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The SIGMA gamma camera problem
• Anger camera: NaI + PMTs• Detector: NaI 1.2 cm thick• 1 GeV P+ energy loss: ~ 10 MeV saturation• Area: 3200 cm2 a proton every 300 µs
(eccentric orbit)• Recovery time > 300 µs• Performance degradation (imaging)
• Solutions:– several smaller cameras unacceptable dead zone
increase– Pixellated camera
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INTEGRAL: an ESA gamma-ray observatory
SPI – The gamma-ray Spectrometer of INTEGRAL. Excellent spectra, good images
IBIS – The gamma-ray Imager onboard the INTEGRAL satellite. Excellent Imaging, good spectra
ISGRI – the IBIS low energy camera (CdTe)
Operations funded till end 2008
Launch: October 2002
Perigee: 10,000 km, Apogee: 150,000 km
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16 CdTeplanar detectors
ASIC (LETI/DSM)
FEE Polycell
ISGRI
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Modular Detection Unit
From SIGMA to IBIS/ISGRI
SIGMA IBIS/ISGRI
Energy range (keV) 40 – 1300 15 - 1000
Angular resolution 18’ 12’
Spectral resolution ∆E/E (100 keV) 13% 8%
Field of view (FWHM) 9.4° x 9.7° 19° x 19°
Timing accuracy 4 s 64 µs
Broad-band sensitivity (100 keV)∆E=E, 3σ, 106s (cm-2 s-1 keV-1)
4 10-6 4 10-7
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Noisy pixels (CdTe detectors)
• Testing thousands of detectors hundreds of them sometime noisy
• A noisy pixel can trigger continuously blind camera !
• What can be done ?– Switch off the noisy pixel– Switch on again the off-pixel after a while– Raise its low threshold
• The Noisy Pixel Handling System (NPHS)implemented on board does all that
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ISGRI in flight behaviour: unexpected effects
• Many pixels automatically disabled– Likely origin: preamp overload multiple triggers
detected as noisy– Problem solved after tuning the Noisy Pixel Handling
system
• Events with zero rise-time (10%)– preamp saturation (E>5 MeV)– Capacitive coupling Trigger
of neighbouring detectors– Easy correction
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ISGRI in flight behaviour: degradation
November 2003Solar flare
-0.7%
-2.6% / year
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The ISGRIThe ISGRI
0°
340°
20°
40°
10°
20°
-10°
-20°
Milky WayMilky Way
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SPI: in-flight annealings
1778,96 keV line
2.88
2.98
3.08
3.18
3.28
3.38
3.48
3.58
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150 155 160 165 170 175 180 185
Revolution number
Resolution in keV
ANNEALING-1
ANNEALING-2
ANNEALING-3
90 K 85 K 85 K 85 K
36 H
36 H
126 H
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Soft gammaSoft gamma--ray astrophysicsray astrophysicsscientific needs for the futurescientific needs for the future
sensitivity imaging Energyrange
Energyresolution
Field of view
X
XXXXXXXXX
XXXX
XX
XX
Fasttiming
X-ray binaries X XX X X
XX
XX
AGNs XX Xpulsars X X XSupernovae XXX X XXSNRs XX XXX XXGRBs X X Xe+e- X XCR interactions XX XX XXISM radioactivity XX XX XX
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Compton telescopeCompton telescope
A basic Compton telescope features twoA basic Compton telescope features two
made of made of scatteringscattering material tomaterial to
layers of position sensitive detectorslayers of position sensitive detectorsθ
11
22
EE11
EE22
scatter the incident gamma rayscatter the incident gamma rayLayer 1:Layer 1:
absorb the scattered photonabsorb the scattered photonmade of made of absorbingabsorbing material tomaterial toLayer 2:Layer 2:
EE00 = E= E11 + E+ E22
cos cos θθ = 1 + m= 1 + meecc22(1/E(1/E00--1/E1/E22))
Both incoming photon energy Both incoming photon energy EE00 and the and the scatter angle scatter angle θθ can be derived from thecan be derived from theEnergy deposits Energy deposits EE11 and and EE22
In addition Compton telescopes allows for polarization studiesIn addition Compton telescopes allows for polarization studies
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Detectors for Compton telescopes• Scattering layer: low Z material (e.g. Si)
– Maximum scattering efficiency– Minimum absorbing efficiency– Minimum doppler broadening– Possibility to measure the electron recoil
• Absorbing layer: High Z material (e.g. CsI, CdTe, CdZnTe)
• For both layers, the best energy resolution is mandatory to achieve a good angular resolution (e.g. Ge)
• The sensitivity depends on the angular resolution
• In fine the energy resolution is the key parameter
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MEGA
• Records both Compton scattering and pair creation
• Electron recoil measurement
• Tracker (scattering layer): Si
• Calorimeter (absorbing layer): CsI
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The advanced Compton telescopeThe advanced Compton telescope
Si(Li) at -40°C or
Ge at -180°C
Wide field Compton instrument dedicated to nuclear astrophysicsWide field Compton instrument dedicated to nuclear astrophysics
Goal: sensitivity < 10Goal: sensitivity < 10--77 cmcm--22 ss--11
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Steps toward a Compton telescope for the NEXT mission
Angular resolution
Stacks of shottkyCdTe diodes
T. Tanaka et al. 2004, SPIE Glasgow
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SWIFTCatching GRBs
Telescope Coded apertureTelescope PSF 17’ FWHMPosition accuracy 1’ – 4’Detector 32k CZT pixelsEnergy resolution 7 keV FWHMTiming resolution 100 µsFOV 2 srEnergy range 15 – 150 keVSensitive area 5200 cm2
Max. trigger rate 195 000 s-1
BAT
XRT
Spacecraft
UVOT
BAT
UVOT
XRT
Barthelmy et al. 2005, AAS
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Study of GRB prompt emission with Study of GRB prompt emission with ECLAIRsECLAIRsSpace gammaSpace gamma--ray telescope ray telescope
coupled to ground based optical telescopescoupled to ground based optical telescopes
Wide field coded mask camera
• Energy range: 3.5 - 300 keV• Field of view: ~ 2 sr• 1024 cm2 shottky CdTe 4x4 mm• Advanced readout electronics
Cou
nts
100
200
300
0
Energy (keV)10 40 605020 30
3.5 keV
CNES microsatellite (2009)
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Ultra deep XUltra deep X--ray survey with EXISTray survey with EXIST
HET: 5.6 square meters of pixel CZT detectors (1.25 mm pitch)
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Detectors for coded-mask soft gamma-ray telescopes
• GRANAT/SIGMA: single large NaI disk + PMTs• INTEGRAL/ISGRI: planar CdTe• INTEGRAL/PICsIT: CsI+PIN-diodes• INTEGRAL/SPI: Cooled HPGe detectors• SWIFT/BAT: planar CZT• ECLAIRS: planar CZT• EXIST: pixel CZT
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Towards a gammaTowards a gamma--ray lensray lensA plane parallel crystal intercepting a beam of very A plane parallel crystal intercepting a beam of very short wavelength radiation λ act as a 3short wavelength radiation λ act as a 3--D D Diffraction array. When entering such a crystal Diffraction array. When entering such a crystal under an angle θ a beam of highunder an angle θ a beam of high--energy photons is energy photons is therefore diffracted under the same angle θ therefore diffracted under the same angle θ defined by the Bragg condition: defined by the Bragg condition: 2 2 d d sin(θ) = sin(θ) = nn λ
diffractedbeam
d
transmittedbeam
λ
A gammaA gamma--ray concentrator (gammaray concentrator (gamma--ray “lens”) could ray “lens”) could then be build in mounting hundreds of such crystals then be build in mounting hundreds of such crystals onto concentric ringsonto concentric rings
Detectors at the focus could be Detectors at the focus could be GeGe, CdTe or CZT, CdTe or CZT
Because of their long focal distance (Because of their long focal distance (> 10 m> 10 m) ) gammagamma--ray concentrators would require two ray concentrators would require two satellites in close formation as in the satellites in close formation as in the MAXMAX mission mission under investigation in France under investigation in France
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The ISGRIThe ISGRI
0°
340°
20°
40°
10°
20°
-10°
-20°
Milky WayMilky Way
Confusion !
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Grazing Incidence Telescopes: Grazing Incidence Telescopes: extending the mirror domainextending the mirror domain
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The Galactic NucleusThe Galactic Nucleus
As seen with INTEGRAL in the As seen with INTEGRAL in the 2020--60 keV60 keV bandbandAs will be seen with SIMAs will be seen with SIMBOLBOL--XX in in 2020--60 keV60 keV bandband
G0.9+0.1
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IBISISGRI
XMMEPIC
SIMBOL-X (CNES-ASI 1-60 keV)
-1000 0 1000 2000 3000 4000 5000 6000 7000 80000
50
100
150
200
250
energy (eV)
coun
ts /
AD
C c
hane
l
T=22 oC
FWHM = 71.5 eV
ENC = 8.43 el r.m.s
FWHM =151.1 eV
DEPFET : 8x8 « macro pixel » 1mm² matrix
256 pixels CdTe
Schottkyarrays,
0.5 mm thick (ACRORAD)
Spectrum withIDeF-X V0
ASIC
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SIMBOLSIMBOL--X SensitivityX Sensitivity
XMM INTEGRALSIMBOL-X
Min
imum
det
ecta
ble
flux
(pho
tons
cm
-2s-1
keV
-1)
Energy (keV)
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HEFT (balloon) - NuSTAR (SMEX 6-80 keV)Detector: pixel CZTPixel size: 500mThickness: 2 mmUnit dimension: 1.3 x 1.3 cmUnits/focal plane: 4∆E/E = 1.4% (FWHM, 70 keV)Elect. noise (rms, leakage incl.) 40 e-
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Focusing telescope for the NEXT mission (1-80 keV)
Caltech – ISAScollaboration
Detector: pixel CdTePixel size: 500µmThickness: 0.5 mmUnit dimension: 2.4 x 1.3 cm
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Conclusions
• Planar Semiconductor detectors such as CdTe, CZT, Ge are currently observing the soft gamma-ray sky from space
• Thanks to their satisfactory in-orbit behaviour (stability, background, degradation) it is now established that they can be safely operated and that they can maintain their performance over long periods of time in space
• More and more projects plan to use semiconductor detectors
• Both focusing and Compton telescope will take advantage of pixel detectors (CdTe, CZT) with their– Fine imaging capability– Enhanced spectral performance
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