Hiroyasu Tajima Stanford Linear Accelerator Center Nov 3–8, 2002 VERTEX2002, Kailua-Kona, Hawaii Gamma-ray Polarimetry ~ Astrophysics Application ~

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.


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.


Soft Gamma-ray (X-ray) Imaging

Coded mask Compton telescope

X-ray mirror Well-type Phoswich


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

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟


Polarimetry with Micro Pattern Gas Detectors

R. Bellazzini, INFN Pisa


Analyzing Power

5.9 keV unpolarized 5.4 keV polarized

Analyzing power = (Cmax Cmax)/(Cmax Cmax) ~ 50%

CmaxCmin


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


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)


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


Source Localization


With 10X Better Resolution…


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.


Collaboration

Hiroyasu Tajima, T. KamaeStanford Linear Accelerator Center

T. Takahashi, K. NakazawaInstitute of Space and Astronautical Science

Y. FukazawaHiroshima University

M. NomachiOsaka University


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


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


-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%


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℃


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)


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


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


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


Prototype System

• AC configuration

• DC configuration

VA32TA

Singled-sided SSD

RC chip


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


Noise (keV)


DC configuration, 0 oC

0

0.5

1

1.5

2


Noise (keV)


120 e–

(RMS)


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



DC 0 oC2 µs 1.2 keV 1.1 keV



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



241Am Fit

56 58 60 62 640

500

1000

1500

2000

2500

3000

3500

241Am59.5 keVFWHM 1.3 keV(2.1%)

Energy [keV]


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



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]


Energy Resolution Summary

Config. Temp. peak

Resolution (FWHM)

60 keV 122 keV

AC





DC 0 oC2 µs 1.6 keV 1.6 keV



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.


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)


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


Germanium Compton Telescope


Documents

Hiroyasu Tajima Stanford Linear Accelerator Center Nov 3–8, 2002 VERTEX2002, Kailua-Kona, Hawaii Gamma-ray Polarimetry ~ Astrophysics Application ~