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Hiroyasu TajimaStanford Linear Accelerator Center
Nov 3–8, 2002VERTEX2002, Kailua-Kona, Hawaii
Gamma-ray Polarimetry~ Astrophysics Application ~
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Outline
• Introduction.• Concepts.• Key features (requirements.)• Instrument description.
Silicon Strip Detector System.• Double-sided SSD.• Low noise front-end VLSI.
• Results. Noise performance. Energy resolution.
• Conclusions and future prospects.
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Polarization in Astrophysics
• Gamma-ray is excellent probe to study particle acceleration mechanism in BHs and pulsars.
• Polarization is important parameter to understand gamma-ray production mechanism. Inverse Compton Scattering.
• Polarization depends on scattering angle.• Geometrical information.
Synchrotron Radiation.• Polarization is perpendicular to magnetic field direction.
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Soft Gamma-ray (X-ray) Imaging
Coded mask Compton telescope
X-ray mirror Well-type Phoswich
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Polarization Measurement
• Photoelectric absorption
• Compton Scattering Polarization depends on scattering angle,
photon energy.
€
∂σ∂Ω
∝Z 5
Eγ
72
sin2 θ ⋅cos2 φ
(1− β e cosθ)4
e
E
E
E’
Polarization vector
€
∂σ∂Ω
∝′ E γ
Eγ
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟
2′ E γ
Eγ
+Eγ
′ E γ− 2sin2 θ ⋅cos2 φ
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Polarimetry with Micro Pattern Gas Detectors
R. Bellazzini, INFN Pisa
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Analyzing Power
5.9 keV unpolarized 5.4 keV polarized
Analyzing power = (Cmax Cmax)/(Cmax Cmax) ~ 50%
CmaxCmin
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Multiple Compton Technique
Proposed by T. Kamae et al. 1987
E1
E3
E2
1
€
cosθ1 =1+mec
2
E1 + E2 + E3
−mec
2
E2 + E3
2
€
cosθ2 =1+mec
2
E2 + E3
−mec
2
E3
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Key Features (Requirements)
• High energy resolution: ~ 1 keV (FWHM).
High angular resolution: ~ 1o (FWHM). High background rejection.
• Constraints from Compton kinematics
• Polarimetry.• Large Field-of-View: > 2 sr.• Wide energy band: 0.05–20 MeV.• Low weight.
No heavy calorimeter.
~ 120 e– (RMS)
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Angular Resolution
0
2
4
6
8
10
0 1 2 3 4 5
Energy resolution (keV)
Angular resolution
(deg)
E=0.1 MeVE=0.2 MeVE=0.5 MeV
Doppler broadening will limit ultimate angular resolution.
0
2
4
6
8
10
0 1 2 3 4 5
Energy resolution (keV)
Angular resolution
(deg)
E=0.1 MeVE=0.2 MeVE=0.5 MeV
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Source Localization
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
With 10X Better Resolution…
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Semiconductor Multiple-Compton Telescope
Single-Layer Interaction Probability
0.001
0.010
0.100
1.000
0.0 0.1 1.0 10.0 100.0
Photon Energy (MeV)
Probability
photo-absorption
ComptonScattering
pair-creation
Si Detector
CdTe Detector
Si
CdTe
Doppler broadening is much smaller in Si.
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Collaboration
Hiroyasu Tajima, T. KamaeStanford Linear Accelerator Center
T. Takahashi, K. NakazawaInstitute of Space and Astronautical Science
Y. FukazawaHiroshima University
M. NomachiOsaka University
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Performance
• Si is essential for wide energy band.
25cm
80layers
80 layers of0.5 mm thick Si and CdTe
Takahashi (ISAS)
Si
Si
Si
CdTe
CdTe
CdTe
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Compton Kinematics
• Background suppression
-10 -8 -6 -4 -20
20
40
60
80
100
120
140
160
180
200
220
Ecal − Emeas
80 2 4 6 10
-3 -2.5 -2 -1.5 -1 -0.5 0 0.5 10
50
100
150
200
250
300
350
400
450
coscal
EGS4.4 MC
€
cosθcal =1+mec
2
E1 + E2
−mec
2
E2
€
Ecal =1
1 E2 + (cosθ −1) mec2
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
-150 -100 -50 05 0 100 1500
5
10
15
20
25
30
35
40
45
φ (deg)
Polarization Sensitivity
EGS4.4 MC
100% polarized, 100 keV|cos| < 0.6
Analyzing power ~ 75%
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Recent Development of CdTe Detector
• Tremendous amount of progress has been made. Highly uniform, fully active sensors can be
produced.
122 keVFWHM1.35 keV
5 oCBias 800V (16 kV/cm)
57Co
No Tail
Takahashi et al. 1999 NIM A 436(see e.g. Takahashi et al. IEEE 2002, June andreview by Takahashi & Watanabe IEEE 2001,48,4)
-25℃
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
CdTe Gamma-ray Imager
5cm Pixel 1.2x1.2mm2 1024 pixels
Pixel 0.2x0.2mm2 1024 pixels
CdTe
Pixel 0.67x0.67mm2 400 pixels
2dim ASIC (100pixel)
2mm
bump bonding
ISAS/MHI Patent Applying
Takahashi (ISAS)
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Si Strip Detector System
• Why Double-sided Si Strip Detector? No self-trigger for CCD. Hybrid-pixel detector increases non-active
material. Monolithic-pixel detector cannot be produced in
large volume.
• System configuration.
V
Double-sidedSi Strip Detector
Front-end VLSIVA32TA
RC chipR
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Double-sided Si Strip Detector
• 2.56cm x 2.56 cm ~1/2 length of full size sensor.
• 300 µm thick, 400 µm pitch, 100 µm gap.• Strip capacitance: ~ 5.5 pF (measured.)
Junction side Ohmic side
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
VA32TA: Low Noise Front-end VLSI
• Low noise Front-end MOSFET geometry optimized for small
capacitance load in 1.2 µm process.
• Internal DAC (4-bit trim DAC, bias).• Fabricated in AMS 0.35 µm process
Radiation hard to 20 MRad.
• SEU (single event upset) tolerant.
Level-sensitive
Discriminator
Semigaussian“fast” shaper
Monostable(fixed width)
Semigaussian“slow” shaper
ChargeIntegrator(preamp.)
S/H
Vss
Vdd
TriggerOut
TAVA
Multiplexer
analog out
€
0.37 + 0.16 × C( ) τ [keV]
€
45 +19 × C( ) τ [e−] (RMS)
Ideas ASA
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Prototype System
• AC configuration
• DC configuration
VA32TA
Singled-sided SSD
RC chip
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Noise Analysis
• Amplifier noise: capacitance load.• Shot noise: leakage current.• Thermal noise: detector bias resistance.
AC configuration, 20 oC
0
0.5
1
1.5
2
0 1 2 3 4Peaking time (µs)
Noise (keV)
Amplifier noiseShot noiseThermal noiseTotal noiseMeasured noise
AC configuration, 0 oC
0
0.5
1
1.5
2
0 1 2 3 4Peaking time (µs)
Noise (keV)
Amplifier noiseShot noiseThermal noiseTotal noiseMeasured noise
DC configuration, 0 oC
0
0.5
1
1.5
2
0 1 2 3 4Peaking time (µs)
Noise (keV)
Amplifier noiseShot noiseThermal noiseTotal noiseMeasured noise
120 e–
(RMS)
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Noise Performance Summary
Config. Temp. peak
Noise (FWHM)
Measured Expected
AC
20 oC2 µs 1.7 keV 1.6 keV
4 µs 1.7 keV 1.6 keV
0 oC2 µs 1.6 keV 1.4 keV
4 µs 1.4 keV 1.1 keV
DC 0 oC2 µs 1.2 keV 1.1 keV
4 µs 1.0 keV 0.9 keV
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
0
200
400
600
800
1000
12002
x10
241Am
59.5 keV
Energy [keV]
13.9 keV
17.6 keV
21.0 keV
26.3 keV
0 10 20 30 40 50 60 70
241Am Spectrum
DC configuration, 0 oC
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
241Am Fit
56 58 60 62 640
500
1000
1500
2000
2500
3000
3500
241Am59.5 keVFWHM 1.3 keV(2.1%)
Energy [keV]
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
57Co Spectrum
100 120 140 1600
500
1000
1500
2000
2500
57Co122.1 keV
Energy [keV]
136.5 keV
0 20 40 60 80
Compton edge
DC configuration, 0 oC
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
57Co Fit
116 118 120 122 124 126 1280
200
400
600
800
1000
1200
57Co122.1 keVFWHM 1.3 keV(1.1%)
Energy [keV]
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Energy Resolution Summary
Config. Temp. peak
Resolution (FWHM)
60 keV 122 keV
AC
20 oC2 µs 1.9 keV 2.1 keV
4 µs 2.1 keV 2.3 keV
0 oC2 µs 1.8 keV 1.9 keV
4 µs 1.7 keV 1.8 keV
DC 0 oC2 µs 1.6 keV 1.6 keV
4 µs 1.3 keV 1.3 keV
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Conclusions and Future Prospects
• Energy resolution measured using prototypes. 1.3 keV @0 oC for 60 and 122 keV X-rays. Noise sources are well understood.
• Imaging test with stacked DSSD prototypes. Polarization measurements.
• Further improvements are required for larger full-sized sensors. Optimization of front-end MOSFET in 0.35 µm process. Reduction of detector capacitance.
• Sensor thickness: 300 µm 400 µm. Pitch adapter.
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
1E-8
1E-6
1E-4
1E-2
1E-2 1E-1 1E+0 1E+1 1E+2 1E+3 1E+4 1E+5
Energy (MeV)
Sensitivity Gap…
Sen
siti
vity
(M
eV/c
m2/s
)• No approved mission to cover 0.1–20 MeV
energy band. Sensitivity is mostly limited by BG.
COMPTEL
EGRET
1E-8
1E-6
1E-4
1E-2
1E-2 1E-1 1E+0 1E+1 1E+2 1E+3 1E+4 1E+5
Energy (MeV)
Astro-E2
GLAST
INTEGRAL
EXIST
OSSE
Next generationCompton telescope
1E-8
1E-6
1E-4
1E-2
1E-2 1E-1 1E+0 1E+1 1E+2 1E+3 1E+4 1E+5
Energy (MeV)
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Liquid Xenon TPC
LXeGRIT collaboration
88Y-Multiple site event
0 1 2 3Energy (MeV)
0
200
400
600
800
898keV
1836keV
88Y Multiple-site events
0 1 2 3Energy (MeV)
0
50
100
150
200
250
300
898keV
1836keV
88 -Y Single site events
Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002
Germanium Compton Telescope