Developments of Si and CdTe Semiconductor Imaging Detectors for a Compton Camera

What we establishedFrom 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 de

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

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.

High Energy Resolution

Low Energy Threshold

Good Position Resolution

several 10 keV — MeV Gamma-rays

DSSD(double-sided Silicon strip

Hard X-ray and Gamma-ray (50 keV MeV)

observation for high energy astrophysics

6 layer DSSDs + 3 CdTe Pixel Detectors

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

DSSD

CdTe

Prototype results S Watanabe et al IEEE Trans Nucl Sci., vol

52, pp.2045-2051, 2005

Compton

Images

Prototype results S Watanabe et al IEEE Trans Nucl Sci., vol

52, pp.2045-2051, 2005

80 keV

Compton

Images

Prototype results S Watanabe et al IEEE Trans Nucl Sci., vol

Prototype results S Watanabe et al IEEE Trans Nucl Sci., vol

Prototype results S Watanabe et al IEEE Trans Nucl Sci., vol

Prototype results S Watanabe et al IEEE Trans Nucl Sci., vol

Experimental Result & Estimation

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)

10 % efficiency

Our Goal

a lot of issues to be done

Further performance study by using Monte Carlo

see Odaka et al Poster in this symposium

DSSD stack

0 10 20 30 40 50 60 1

10

2 10

3 10

4 10

4cm x 4cm

size: 2.6 cm x 2.6 cmthickness: 0.3 mm

stack pitch: 5.4 mm

See Takeda et al Poster in this symposium

Stacking More Compactly

reduce material around DSSD

High Energy Resolution CdTe Detector

 diode type ( In -> anode, Pt -> cathode)

ISAS/JAXA and ACRORAD(JAPAN)

2 mm x 2 mm x 0.5 mm

137 Cs

FWHM 2.1 keV 662keV

● Extremely low leakage ● High bias voltage

10 pA for 2x2x0.5mm 2 at 20℃ at 500 V

but, low-mobility and short life time of carriers (especially holes)

thin CdTe diode device -> high energy resolution and fully active device

~Fano limit

CdTe Pixel Module

thickness: 0.5 mm

8x8 = 64 pixelsCdTe

ASIC

In Pt(pixel)

ASIC

ASIC: VA64TA (ISAS, SLAC and IDEAS)

low power consumption: 0.2mW/ch

7 mm

Performance of the CdTe Pixel Module

14.4 keV FWHM 1.1 keV

Energy [keV]

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

stack pitch : 2 mm

1024 ch

Absorber for the next Compton camera

2x2 CdTe pixel modules are

Plan of the next Compton camera

CdTe Pixel

DSSD

4 layers DSSD stack+ 4 layers CdTe pixel stack+ 8 CdTe pixels placed on the side of DSSDs

Applications of the CdTe Pixel module

5 ~ 10 mm

Once we establish the module, we can expand it to…

stacked detector

high efficiency and high energy

resolution gamma-ray detector

Applications of the CdTe Pixel module

5 ~ 10 mm

Once we establish the module, we can expand it to…

stacked detector

high efficiency and high energy

resolution gamma-ray detector

4 ~ 8 cm

Large Area Imager

Large Area CdTe Imager

0 5 10 15 20 25 30 35 0

5 10 15 20 25 30 35

0 100 200 300 400 500 600 700

Large Area CdTe Imager Result

A plant(tobacco) drinking in

Adding tungsten collimator

-> Gamma Camera

Large Area CdTe Imager Result

A plant(tobacco) drinking in

Adding tungsten collimator

 New CdTe pixel modules

 good energy resolution, Uniform

 New Si/CdTe Compton camera is now underway

 Other Application of CdTe pixel detector

 Stacked Detector

 Large area Detector