Soft Gamma-ray Detector (SGD) for the NeXT mission and beyond…

T.Takahashi, Astronomy with Radioactivies IV,2003

Soft Gamma-ray Detector (SGD)for the NeXT mission

Tadayuki Takahashi

Institute of Space and Astronautical Science

(ISAS, Japan)

g-rayDetector

1979 1983 1987 1993

2005

ISAS/U-Tokyo/SLAC/Hiroshima U./Osaka U./Saitama U./Riken/Kanazawa U. (the SGD collaboration)

2010?

and beyond…Astro-E2


Introduction- filling the sensitivity gap -

Gap-1 Gap-2

• Development of highly-sensitivedetector in Soft Gamma-ray energybands (sub-MeV & MeV) is crucialissue.

• Our Approach• Extend the energy coverage

from X-ray to higher energy(from Gap-1 to Gap-2)

• Multi-band observation (fromX-rays) is important (andproductive), to study theNON-THERMAL universe.

• Apply the developed-technology to higher energyband for the Gap-2

The NeXT (New X-ray Telescope) mission– Next generation “Multi-band” mission to studythe non-thermal universe

(6th X-ray satellite in Japan, hope to be launched in 2010)


Spectrometer

Hard X-ray Imager

SGD

What’s ‘next’ in the NeXT mission• Super Mirror + Hard X-ray Imager

• High resolution X-ray detector (FWHM = 3 eV at 6 keV)• Soft Gamma-ray Detector (30 keV - 600 keV) (+polarization)

Super Mirror ( 0.5-80 keV )

Hard X-ray Imager

focal length8 - 12 m

g-rayDetector

ISAS

30’’ HPD


137Cs

FWHM2.1 keV

662keV

High Resolution CdTe detector- New Detector Material for the future mission -

• High Z semiconductor (ZCd = 48, ZTe = 52)

-> Significant Progress in 1990’s(Takahashi et al. IEEE NS49, 3,2002, review by Takahashi &Watanabe, IEEE NS48, 4, 950, 2001)

see posters by Tanaka et al.and by Mitani et al.

ISAS projectHigh Energy Resolution

12.8mm

Fine Position Resolution

CdTe Gamma-ray Imager(pixel size 200 µm)

ISAS & Bonn U.


To improve the sensitivity in the sub-MeV region

Key issues:

HXD Concept (High Signal to Background ratio)• tight active shields (Well-type shield)• the collimated narrow field of view (0.5 degree at 100 keV, 4 degree at 500keV by a fine collimator and BGO)• Compton suppression for high energygamma-ray• the compound-eye configuration.

• Cosmic X-ray Background (CXB) from the FOV• Non X-ray Background (Internal Background)• Confusion Limit in the FOV/Error circle

How can we improve this for the NeXT?Internal Background limits the sensitivity.

Si

GSO

10-600 keV HXD for Astro E-2BGO


Semiconductor Compton Telescopefor the pointing observation…

Stack of Si strips

High Resolution CdTe pixels

If we replace GSO+Si PIN diode usedin the HXD by ….

CG by Yuriko S

Well-type Active shield

and put them into the well…


New Concept: Narrow FOV Compton Camera•　Gamma-rays from the source comefrom the “narrow” FOV (0.5-3 degFWHM) (Direction is Given!)

Select two hits events andaccept only if

†

E2 =(E1+ E2)

1+(E1+ E2)(1- cosq)

mec2

No need to worry about the sequenceif scattering angle is below…

First scattering (E1) has lower energy

This condition is expected to get rid of most of internal background.

(Takahashi et al. 2003, SPIE, vol. 4851)(Adoption of Fine Coll. is still an option)


• Lower accidental coincidences• Imaging capability withan angular resolution of ~degree,→ Important for modeling the backgroundspectrum for the Non-Compton mode

Narrow FOV Compton Camera


• Lower accidental coincidences• Imaging capability withan angular resolution of ~degree,→ Important for modeling the backgroundspectrum for the Non-Compton mode

Narrow FOV Compton Camera •24 layers of 0.5 mm-thick Strip Strip detectors

•6 mm-thick CdTe Pixel (res. 1mm)

Effective Areatotal

one Compton+ Abs.

Polarization (Scattered at Si and absorped in CdTe)

(200 keV)


Key technologiesunder development

1. High resolution Silicon Strip detector2. High resolution CdTe pixels/strips

(see posters by Mitani and Tanaka)3. Low Noise ASIC 4. Signal extraction (bump bonding)

Si strip with a new ASIC

0

200

400

600

800

1000

12002x10

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

ΔE =1.5keV(FWHM)

25mm/400micron pitch

Uno etal., 2003

Tajima et al. 2003, SPIE, 4851

Takahashi etal., IEEE, NS. 48, 3,2001


Compton Reconstruction

Tajima, Uno, Mitani, Nakazawa, Takahashi, Fukazawa et al.


Sensitivity of the NeXT mission0.3 - 600 keV

– High Sensitivity for both Line and Continuum

– Polarization measurement 100 ks

CasA

Line Cont.

This is not the end of the story…

68keV


Semiconductor Multi Compton Telescope(SMCT)

For the future MeV Gamma-rayAstronomy

Maybe by a big mission Or by a small satellite

Or by a formation flight

Or by a balloon


CdTe telescope• CdTe has a high Compton Efficiency for the energy above 300 keV ( Eff. = 40% at 1MeV for 80 layers , 250 cm2)　Compact Compton Telescope for micro/small satellite(important to increase chances of the mission)

25cm

80layers

80 layers of0.5 mm thickCdTe (and/or Si)

Conceptual design of CdTe SMCT

Si

Si

Si

CdTe

CdTe

CdTe

Eff. of MultiCompton

Note: Angular resolution

Large FOV

Polarization


Active Pair Telescope (APT)Above 10 MeV, Pair Production is the dominant process

radiation length (r.l.)of CdTe:1.52cm

-> can be used as an active CONVERTER as well as a calorimeter (total r.l. -> 2.6 r.l. for80 layers )

0.5 mm thick CdTe --> 0.03 r.l(same as the conversion foil used in GLAST)

Highly Sensitivedetector below 100 MeV

Fully active pair production telescopeGLAST Gamma-ray below 100 MeV would be absorbed by conversion foil (loose efficiency)

CdTe APT

(Takahashi et al. 2003, SPIE, vol. 4851)


Summary• Development of High Resolution CdTe and Si

strips/pixels are in progress.– Pixels, Strips and related technology for CdTe/CZT/Si

are now well in our hands.– ex. Focal plane detector for the super mirror

• New detector concepts– Narrow FOV Compton telescope (SGD) for the NeXT

mission (upto several hundred keV, polarization)– Semiconductor Multi Compton Telescope (SMCT) for

MeV gamma-rays– Active Pair-production Telescope (APT)

• For the demonstration, we will have balloonmissions in 2003-2006.

Documents

Soft Gamma-ray Detector (SGD) for the NeXT mission and beyond…