Mô tả:
Developments of Si and CdTe
Semiconductor Imaging Detectors
for a Compton Camera
Shin Watanabe(ISAS/JAXA)
Shin'ichiro Takeda, Shinnosuke Ishikawa, Hirokazu Odaka, Masayoshi Ushio,
Takaaki Tanaka, Kazuhiro Nakazawa, Tadayuki Takahashi (ISAS/JAXA),
Hiroyasu Tajima (SLAC),
Yasushi Fukazawa (Hiroshima Univ.)
Sep. 14, 2006, the Sixth International
“Hiroshima” Symposium @Carmel
Concept of the Si/CdTe Compton Camera
Hard X-ray and Gamma-ray (50 keV -- MeV)
observation for high energy astrophysics
Si -> Scatterer, CdTe->Absorber
Si (Z=14)
Low Photo Abs.
High Compton Scattering
CdTe (Z=48, 52 ρ~5.8 g/cm3)
High Photo Abs.
DSSD(double-sided Silicon strip
detector) 20-30 layers
4-5 cm
several 10 keV — MeV Gamma-rays
CdTe Pixel Detectors
High Energy Resolution
Symmetrically Placed
Low Energy Threshold
Good Position Resolution
Precise Gamma-ray photon Tracking
NeXT mission (JAXA, 201?)
Prototype
6 layer DSSDs + 3 CdTe Pixel Detectors
DSSD
CdTe
DSSD: (with Hamamatsu Photonics)
2.6 cm × 2.6 cm, 300µm thickness
64 strips (each side) 400µm pitch
CdTe Pixel: (with ACRORAD)
Single Crystal CdTe (THM)
In/CdTe/Pt (Diode type)
2 mm x 2 mm pixel, 8x8=64 pixels
0.5 mm thickness, Bias 400V
Prototype results
Compton
Images
S. Watanabe et al. IEEE Trans. Nucl. Sci., vol.
52, pp.2045-2051, 2005
Prototype results
Compton
Images
80 keV
S. Watanabe et al. IEEE Trans. Nucl. Sci., vol.
52, pp.2045-2051, 2005
Prototype results
Compton
Images
80 keV
122 keV
S. Watanabe et al. IEEE Trans. Nucl. Sci., vol.
52, pp.2045-2051, 2005
Prototype results
Compton
Images
80 keV
122 keV
270-400 keV
S. Watanabe et al. IEEE Trans. Nucl. Sci., vol.
52, pp.2045-2051, 2005
Prototype results
Compton
Images
80 keV
122 keV
270-400 keV
511 keV
S. Watanabe et al. IEEE Trans. Nucl. Sci., vol.
52, pp.2045-2051, 2005
Prototype results
Compton
Images
S. Watanabe et al. IEEE Trans. Nucl. Sci., vol.
52, pp.2045-2051, 2005
80 keV
Experimental Result & Estimation
Experiment
122 keV
Doppler Eff.
Position Res.
Energy Res.
Total
270-400 keV
511 keV
Doppler Effect is Dominant
What we established
From the prototype experiments,
we have found that a Si/CdTe Compton Camera
can achieve the theoretical limit (Doppler broadening)
•
~a few degree (@ > 500 keV), ~ 10 degrees (@100 keV)
•
~ 0.7--1.0 mm, 3.5 mm at 2 cm
DSSD(double-sided Silicon strip
detector) 20-30 layers
4-5 cm
Our Goal
1%(FWHM) Energy resolution
Doppler limit angular resolution
10 % efficiency
Further performance study by using Monte Carlo
see Odaka et al. Poster in this symposium
CdTe Pixel Detectors
Symmetrically Placed
a lot of issues to be done
DSSD stack
See Takeda et al. Poster in this symposium
Stacking More Compactly
size: 2.6 cm x 2.6 cm
thickness: 0.3 mm
stack pitch: 5.4 mm
reduce material
around DSSD
improve
Compton efficiency
larger size
241Am
4cm x 4cm
Nside Channel
4 layers
2 mm pitch
1st layer
FWHM 1.5 keV 2nd layer
@ 60 keV
3rd layer
4th layer
104
190
180
180
160
170
140
160
3
10
120
150
Gamma-rays
100
140
80
130
60
120
110
20
100
0
102
40
10
20
30
40
50
60
70 80 90
Pside Channel
Shadow Image
(log scale)
0
10
FWHM 1.5 keV
@ 60 keV
thicker
larger
0.5 mm thick 5 cm x 5 cm
1
0
10
20
30
40
50
60
Energy[keV]
stacking more layers
High Energy Resolution CdTe Detector
ISAS/JAXA and ACRORAD(JAPAN)
CdTe (Z=48, 52 ρ~5.8 g/cm3)
good for gamma-ray
but, low-mobility and short life time of carriers (especially holes)
diode type ( In -> anode, Pt -> cathode) ●
Extremely low leakage
10 pA for 2x2x0.5mm2 at 20℃ at 500 V
2 mm x 2 mm x 0.5 mm
●
High bias voltage
137Cs
662keV
FWHM 2.1 keV
~Fano
limit
thin CdTe diode device -> high energy resolution and fully active device
CdTe Pixel Module
CdTe
area: 11.2 x 11.2 mm2
thickness: 0.5 mm
pixel size: 1.4 x 1.4 mm2
8x8 = 64 pixels
ASIC
In/Au Stud Bump
Al2O3 fanout board
wire-bonding
In
ASIC
Pt(pixel)
ASIC: VA64TA (ISAS, SLAC and IDEAS)
low noise: 50-60 e- RMS
low power consumption: 0.2mW/ch
7 mm
Performance of the CdTe Pixel Module
Sum Spectrum
5ºC, 600V
57Co
All spectra from 64 pixels
122 keV
FWHM 1.5 keV
2000
1800
1600
1400
1200
1000
14.4 keV
FWHM 1.1 keV
800
600
400
200
0
0
20
40
60
80
100
Energy [keV]
120
140
Uniformity is good.
~50 CdTe pixel modules have been constructed.
almost same performance
Absorber for the next Compton camera
2x2 CdTe pixel modules are
stacked in 4 layers
1024 ch
stack pitch : 2 mm
Absorber for the next Compton camera
2x2 CdTe pixel modules are
stacked in 4 layers
1024 ch
133Ba
gamma-rays
104
ALL
1st layer
2nd layer
3rd layer
4th layer
103
102
10
1
0
50
100
150
200
250
Energy[keV]
300
350
400
stack pitch : 2 mm
Energy Resolution(FWHM)
2.0 keV@122 keV
3.0 keV@356 keV
ΔE/E ~ 1 %
Plan of the next Compton camera
DSSD
CdTe Pixel
4 layers DSSD stack
+ 4 layers CdTe pixel stack
+ 8 CdTe pixels placed on the
side of DSSDs
Applications of the CdTe Pixel module
Once we establish the module, we can expand it to…
stacked detector
5 ~ 10 mm
high efficiency and high energy
resolution gamma-ray detector
Applications of the CdTe Pixel module
Once we establish the module, we can expand it to…
stacked detector
5 ~ 10 mm
Large Area Imager
high efficiency and high energy
resolution gamma-ray detector
4 ~ 8 cm
Large Area CdTe Imager
4x4=16 CdTe pixel modules
5.4 cm x 5.4 cm large area imager
Shadow Image 30--150 keV
5.4cm
φ3mm
M5 Nut
700
35
30
600
25
500
20
400
15
300
10
200
5
100
0
0
5
10
15
20
25
30
35
0
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