A Si/CdTe Semiconductor Compton Camera
Shin Watanabe, Takaaki Tanaka, Kazuhiro Nakazawa, Takefumi Mitani, Kousuke Oonuki, Tadayuki Takahashi,
Takeshi Takashima, Hiroyasu Tajima, Yasushi Fukazawa, Masaharu Nomachi, Shin Kubo,
Mitsunobu Onishi and Yoshikatsu Kuroda

Ein

Abstract— We are developing a Compton camera based on
Si and CdTe semiconductor imaging devices with high energy
resolution. In this paper, results from the most recent prototype
are reported. The Compton camera consists of six layered doublesided Si Strip detectors and CdTe pixel detectors, which areread out with low noise analog ASICs, VA32TAs. We obtainedCompton reconstructed images and spectra of line gamma-rays
from 122 keV to 662 keV. The energy resolution is 9.1 keV and14 keV at 356 keV and 511 keV, respectively.

Si

θ
E1

Index Terms— Compton Camera, Silicon radiation detectors,
CdTe, Gamma-ray spectroscopy detectors, Gamma-ray astronomy
detectors

CdTe
E2

I. I NTRODUCTIONTHE Compton camera is the most promising approachfor gamma-ray detection ranging from several tens keV
to several MeV, especially in high energy astrophysics. In a
Compton camera, the deposited energy and position of the
gamma-ray interactions with the detector are obtained. Whena gamma-ray photon is scattered in one detector and absorbed
in another detector, the incident energy of the gamma-ray andthe scattering angle can be determined as,Ein= E1 + E2
(1)
me c2
me c2
cos θ = 1 −
+
,
(2)
E2
E1 + E2
where E1 is the energy of the recoil electron, E2 is the energyof the scattered photon and θ is the scattering angle.
As shown in eq. (2), the incident direction of a gammaray is calculated from the position and energy information of
the interactions. Therefore, employing imaging spectrometers
as components of Compton cameras, with their good energy
and position resolution, will dramatically improve the angularresolution and hence the sensitivity. From this point of view,
S. Watanabe, K. Nakazawa and T. Takashima are with Institute of Spaceand Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara,
Kanagawa, Japan.
T. Tanaka, T. Mitani, K. Oonuki and T. Takahashi are with Institute of Spaceand Astronautical Science, Japan Aerospace Exploration Agency, and also with
Department of Physics, University of Tokyo, Bunkyo, Tokyo, Japan.
H. Tajima is with Stanford Linear Accelerator Center, Menlo Park, CA,USA.
Y. Fukazawa is with Department of Physics, Hiroshima University, Higashi
Hiroshima, Hiroshima, Japan.
M. Nomachi is with Laboratory of Nuclear Studies, Osaka University,
Toyonaka, Osaka, Japan.
S Kubo is with Clear Pulse Ltd., Ohta, Tokyo, Japan.
M. Onishi and Y. Kuroda are with Nagoya Guidance and Propulsion System
Works, Mitsubishi Heavy Industries, Ltd., Komaki, Aichi, Japan

Fig. 1.

Schematic picture of our Si/CdTe semiconductor Compton camera.

Compton cameras based on semiconductors, such as Si, Ge,
CZT and CdTe, have been proposed and developments are ongoing in many groups [1]–[7]. A Compton camera also enables
us to measure polarization of gamma-rays, through obtaining
the azimuthal distribution of Compton scattering [8], [9].
Based on our developments for CdTe and Si detectors [10]–[14], we have proposed a new Si/CdTe semiconductor Compton
camera. Fig. 1 shows the basic concept of the Si/CdTe Compton
camera. Si detectors are used as scatterers, and CdTe detectors
are used as absorbers. The combination of Si and CdTe issuitable for detection of gamma-rays from several tens keV to afew MeV. The photo-absorption cross section of Si is small, andthe Compton cross section becomes relatively large because of
the small atomic number of Si (Z = 14). Additionally, Si works
better than other materials with larger atomic numbers in termsof the “Doppler broadening” effect [15]. On the other hand,
CdTe has high photo absorption efficiency for gamma-rays ofthis energy region, due to their high atomic numbers of 48 and52.
We have been developing prototypes composed of doublesided Si strip detectors (DSSDs) and CdTe pixel detectors. With
the first prototype consisting of one DSSD and two CdTe pixel
detectors, we have obtained Compton reconstructed images andspectra from 80 keV to 356 keV [16], and have demonstrated
the ability to detect polarized gamma-rays [17]. In this paper,
we report the results from our second prototype of the Si/CdTe
Compton camera. The prototype consists of six layered DSSDs
and three 8 × 8 CdTe pixel detectors.

Fig. 4. The 8 × 8 CdTe pixel detector. The signal from each pixel is fed into
VA32TAs on the FEC.
(a)

(b)

B. CdTe Pixel Detectors
Fig. 2. (a): The double-sided Si strip detector (DSSD). (b): A shadow picture
obtained with the DSSD. 22 keV X-rays are used.

Fig. 3.

We use 8 × 8 CdTe pixel detectors as absorbers in theCompton camera. The CdTe pixel detector is based on the
Schottky CdTe diode device, utilizing indium as the anodeand platinum as the cathode. By utilizing diode structure, we
can obtain high energy resolution [10]–[12]. Fig. 4 shows apicture of the pixel detector. The detector has dimensions of
18.55 mm × 18.55 mm and a thickness of 500 µm. The indium
side is used as a common electrode and is biased with a voltage
of 400 V. The platinum side is divided into 8 by 8 pixels
surrounded by a guard ring with a width of 1 mm. The pixel
size is 2 mm × 2 mm, and the gap between the pixels is 50 µm.
Each pixel is connected to a fanout board by using In/Au studbump bonding technology [19]. The signal from each pixel is
fed into the VA32TAs on-board the FEC. The VA32TA andFEC design are the same as that used in DSSD readout.

The six layered DSSDs. The pitch between DSSD layers is 5.4 mm.

C. Compton Camera Setup
II. S ETUP
A. Stacked DSSDs
For the Compton scatterers, we use DSSDs with an area of
2.56 cm × 2.56 cm and a thickness of 300 µm. The strip pitchof the DSSD is 400 µm and 64 strips are implemented on eachside.
The signals from the strips are processed by front-end-cards(FECs) on which two low noise analog ASICs, VA32TAs [18]are mounted. The strips on the p-side are connected directly
to the input of the ASIC, while the strips of the n-side areconnected via coupling capacitors. In order to obtain full
depletion of the device, the n-side is biased with a voltageof 110 V. Since the spectral resolution of the p-side is better
than that of the n-side, we have created spectra from the pstrips, and data from the n-strips are only used for positional
information.
Fig. 2 shows a picture of the DSSD and a shadow image
obtained with it. The shadow mask is a bookmark made ofbrass covered with gold, whose thickness is 0.8 mm. The imageis created by collecting 22 keV X-rays from a 109 Cd source.
In order to increase the efficiency of Compton scattering, westack six DSSDs. A picture of the six-layered DSSD is shownin Fig. 3. The gap between each DSSD layer is 5.4 mm.

By combining the stacked DSSDs and three CdTe pixel detectors, we constructed a prototype Compton camera. A pictureof the prototype is shown in Fig. 5. Two CdTe pixel detectors
are placed underneath the DSSDs, and another detector isarranged on the side of the DSSDs.
A schematic diagram of the readout electronics is shownin Fig. 6. Signals from all detectors are fed into VA32TAs
mounted on FECs. Fifteen FECs are connected to the interface card (IFC). The IFC provides bias currents/voltages for
VA32TAs, and repeater functions for digital and analog circuitin the ASIC. The readout card (ROC) performs analog-todigital conversions and readout sequence controls. A packetof data is constructed event by event in the ROC, and is sent
to an acquisition computer via the serial data interface basedon Space Wire network [20]. Detailed information on IFC and
ROC is described in the paper of Mitani et al. [21]. In thisprototype, the signals from the comparator outputs from thep-sides of six layered DSSDs and three CdTe pixel detectors
are ORed to make trigger pulses. With each trigger, the pulse
heights of all channels are acquired.
III. DATA A NALYSIS AND R ESULTS
Using radio isotopes, we acquired data with the prototype
to test the imaging and spectroscopy capabilities as a Compton
camera. We placed the radio isotopes 350 mm above the surface

A gamma-ray
sourceFECs
N-SideIFC

ROC
AnalogMPX

DSSDs

P-SideCdTe Pixel
Detectors

TRIG

ADC

Data

CTRL
&
Repeater

TRIG/CTRL
PacketGeneration
TRIG

Bias

Fig. 6.

The schematic diagram of the readout system.

Fig. 7. The relation between ADC channel and energy is shown (a) for a
strip of the DSSD and (b) for a pixel of the CdTe. The dots are obtained frompositions of photo-absorption peaks. Additionally, for DSSDs, we also used
the position of Compton edge of the 511 keV line. The lines show the third
natural spline curves connecting all dots.

Fig. 5.

The prototype of the DSSD/CdTe Compton Camera.

of the top DSSD. The strengths of the used isotopes are 1–
3 MBq. Although there is no system to measure the dead time inour setup, the acquisition times of the following measurements
are for several days in the real time. The DSSDs and the CdTe
detectors were cooled to −5◦ C.
A. Single Hit Events
In order to reconstruct Compton events, relations between an
ADC channel of a pulse height and an actual energy deposit
must be obtained precisely. Therefore, we analyzed “single-

hit events” and obtained photo-absorption peaks of gammaray lines from radio isotopes. The “single-hit” means that only
one channel of the DSSDs or the CdTe pixel detectors has apulse height above specified levels in the ADC unit. The levels
correspond to about 15 keV and 25 keV for DSSDs and CdTe
pixels, respectively.
Fig. 7 shows relations between ADC channel and energy
for a DSSD strip and a CdTe pixel as typical examples. For
DSSDs, in addition to the positions of photo-absorption peaks,
positions of 511 keV Compton edges (341 keV) are used. As
shown in the plots of Fig. 7, the energy deposits are not simply
proportional to the ADC channels. Therefore, we adopted third
neutral spline curves connecting all measured points for thecalibration formula.
By using the relations obtained above, sum spectra of “single
hit events” are created. Fig. 8 shows the spectra of DSSD ((a))
and CdTe pixel detector ((b)). The energy resolutions derived

(a) DSSD(b) CdTe

Fig. 8. The “single hit” spectra created from the DSSD events (a) and the
CdTe events (b).

from these spectra are plotted in Fig. 9. The full-width-at-halfmaximum (FWHM) of the DSSD is ∼ 2 keV regardless of theincident energy. Therefore, this energy resolution is attributable
to the readout system. On the other hand, the FWHM of CdTe is
proportional to the incident energy, and ∆E/E is about 2.5 %.
This tendency means that the major contributor to the energy
resolution is the charge loss due to low mobility and shortlift-time of carriers in CdTe [25]. Though higher bias voltage
should improve the energy resolution of CdTe, we kept the bias
voltage of 400 V with the emphasis on stable operation.
B. Compton Reconstruction
For Compton reconstruction, data reduction is performed asfollows. Firstly, “two-hit events”, one hit in a DSSD and one
hit in a CdTe, were selected from all the data. Here, one hit
in a DSSD means that only one channel that is connected to a
DSSD has a pulse hight above 8 keV, and one hit in a CdTe
means that the only one channel that is connected to a CdTe
detector has a pulse height above 20 keV. From each twohit event, the information on the energy deposits detected in
the DSSD (ESi ) and in the CdTe detector (ECdTe ) and their
hit positions are obtained. Secondly, we calculate the incident
gamma-ray energy (Eγ ) and the scattering angle (θComp ). In
the calculations, we assumed that incident gamma-rays arescattered in the DSSD and fully absorbed in the CdTe pixel
detector. On this assumption,
Eγ = ESi + ECdTe ,(3)

Fig. 9.
The energy resolutions of (a) DSSD and (b) CdTe. For DSSD,
the achieved energy resolution is about 2.0 keV regardless of energy. On theother hand, the energy resolution of CdTe is proportional to energy. ∆E/E is∼ 2.5 %.

andµcos θComp = 1 −

me c2
me c2
−
ECdTe
ESi + ECdTe

¶
.

(4)

From the calculated scattering angle and the two-hit positions, aCompton cone is drawn on the sky event by event. We projected
the cone onto the plane at the distance of 350 mm, and obtained
the image of the gamma-ray source.
Fig. 10 shows the Compton reconstructed images obtainedwith the prototype. A circle with a radius of 5 degree is drawn
together with each image as reference. Fig. 10 (a) is the imageof 57 Co 122 keV gammay-rays, by selecting events in which
the sum of energy deposits at the DSSD and the CdTe pixel
detector is within 118–128 keV. The image of 133 Ba events
above 260 keV is shown in Fig. 10 (b). Fig. 10 (c) and (d) are
images of 22 Na and 137 Cs, respectively. The selected energy
regions are 500–520 keV and 650–675 keV, respectively. We
note that the images are asymmetric because the arrangementof CdTe absorbers is not symmetric. Additionally, the “bananashape” image of 57 Co 122 keV is caused by the fact that the
scattering angle must be larger than 45◦ to deposit an energy
larger than 8 keV at the DSSD, which is the energy thresholdin this analysis.
In order to evaluate the angular resolution of our prototype Compton camera, we compare the calculated Comptonscattering angles (θComp ) with those defined by the locationof gamma-ray source and hit positions (θGeom ) (see Fig. 11).
The difference between the two values reflects the angularresolution of the Compton camera. We examined the distri-

800

800

°

radius 5

600

0.3

600

400

0.25

400

0.2

0
0.15

-200
0.1

-400
-600
-800
-800 -600 -400 -200

0 200 400 600 800
x [mm]

0

0.1

-200

0.08

-800
-800 -600 -400 -200

0.02
0 200 400 600 800
x [mm]

0.2

0.18

°

radius 5

600

0.16

400

0.14
0.12

0.15

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0.1

-400

y [mm]

200

0

0.1

0

0.08

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0.06

-400

0.04

0.05
-600

-600

-800
-800 -600 -400 -200

0 200 400 600 800
x [mm](c) 22 Na 511 keV
Fig. 10.

0(b) 133 Ba 276, 303, 356, 384 keV

200
y [mm]

0.04

0

800

400

0.06

-400
-600

0.25

600

0.12

0.05

°

radius 5

0.16
0.14

(a) 57 Co 122 keV

800

0.18

200
y [mm]y [mm]

200

0.2

°

radius 5

0

0.02

-800
-800 -600 -400 -200

0 200 400 600 800
x [mm]

0(d) 137 Cs 662 keV

Compton reconstructed images of 57 Co, 133 Ba, 22 Na and 137 Cs. Circles with a radius of 5 degrees are drawn together with the images.

bution of θComp − θGeom for various peaks of 57 Co (122 keV
and 136 keV), 133 Ba (356 keV), 22 Na (511 keV) and 137 Cs(662 keV). In Fig. 11, the distribution of θComp − θGeom for
511 keV events is shown as an example. The FWHM of these
distributions, which is the angular resolution of the Compton
camera, is plotted against the incident energy in Fig. 12. The
angular resolution becomes better as the incident gamma-ray
energy becomes higher.
We estimated the contributions of the position and theenergy resolution of the DSSD and the CdTe detector. The
contribution of the position resolution (∆θpos ) is estimated byusing the actual hit positions obtained from the experimentand the strip/pixel size of the DSSD and the CdTe detector.
To estimate the contribution of the energy resolution (∆θene ),we used the Compton-scattering angles of actual events andsmoothed them with the detector energy resolutions derived
from “single-hit” events, which are ∆E ∼ 2.0 keV (FWHM)
and ∆E/E ∼ 2.5 % (FWHM) for the DSSD and the CdTe
pixel detector, respectively. In Fig. 12, the estimated values areplotted.
The other contributions to the angular resolution include theeffect of “Doppler broadening”. The Compton reconstruction
is performed on the basis of eq. (3) and eq. (4), in which
the target electrons are assumed to be free and at rest. In realdetectors, however, target electrons are bound to their atomic
nuclei with non-zero orbital momentum. The uncertainties ofthe bounding energy and the orbital momentum lead to thedegradation of the angular resolution in Compton cameras.
This effect is known as Doppler broadening [22]. In orderto estimate the amount of Doppler broadening, we perform aMonte Carlo simulation using the Geant4 package [23]. As thecode of Compton scattering including Doppler broadening, we
use the package developed by R.M. Kippen [24]. In Fig. 12, theestimated values (∆θDB ) from the simulation are also plotted.
The effect of the Doppler broadening becomes smaller as theincident energy becomes higher, because the binding energy
and momentum of electrons in materials become relatively
small for gamma-ray photons with higher energies. In the same
figure, the total values of ∆θpos , ∆θene and ∆θDB :q∆θtotal = (∆θpos )2 + (∆θene )2 + (∆θDB )2(5)
are plotted together with the experimental data. The experimental values can be explained by the three contributions. In mostcases, the angular resolution is limited by the effect of Doppler
broadening, except that the contribution of position resolution iscomparable to that of Doppler broadening in the higher energy
region (> 500 keV).
In order to obtain a clearer image, there is room for improvement in the arrangement of DSSD scatterers and CdTe
absorbers. Because the Doppler broadening is restrained in thesmaller scattering angles [7], [16], the arrangement that enables
to pick up more events with a small scattering angle should
contribute to make a clearer image. Since small angle scatters
are associated with low energy scattering electrons, a lower
energy threshold for DSSD becomes also important to pick up

Position of the Source(known)

γ
θGeom
DSSD

CdTe pixel

Fig. 11. Definition of θGeom and distribution of θComp −θGeom for 511 keVevents.

such events. Additionally, in order to obtain undistorted images,
symmetric arrangement of CdTe absorber is indispensable.
The energy spectrum of a Compton camera can be obtained
from the sum of energy deposits. The dashed line in Fig. 13
shows the spectrum obtained by simply summing the energies
for all “two-hit events”. In the spectrum, the four gamma-ray
peaks (276 keV, 303 keV, 356 keV and 384 keV) from 133 Ba
cannot be identified clearly. In a Compton camera, we canselect events by using the Compton reconstructed image. The
solid line spectrum drawn in Fig. 13 is made from the events
satisfying the condition that the drawn Compton cone meetsat the source position. The gamma-ray peaks are enhanced
and four peaks are clearly resolved. The energy resolution is
9.1 keV (FWHM) at 356 keV.
Spectra of higher energy gamma-rays are shown in Fig. 14.
The upper panel of Fig. 14 shows the spectrum of 22 Na, andthe lower one shows the 137 Cs spectrum. The achieved energy
resolutions are 14 keV (2.7 %) and 18 keV (2.7 %) at 511 keV
and 662 keV, respectively. These values are consistent with theenergy resolution of the DSSD (∆ESi (FWHM) ∼ 2.0 keV) andthe CdTe pixel detector (∆ECdTE /E ∼ 2.5 %), i.e. the energy
resolution of this Compton camera is expressed asp∆E = (∆ESi )2 + (∆ECdTe )2 ,(6)
In the case of this experiment, the energy resolution of the CdTe
pixel detector limits the spectroscopic ability of this prototype.
As discussed in § III-A, the energy resolution of the CdTe
pixel detector is attributable to the charge collection efficiency.
A higher bias voltage of > 1000 V for 0.5 mm thickness isFig. 12. Relation between incident gamma-ray energy and angular resolution.
Filled circles show the experimental data. Open triangles, squares and diamonds
are estimated contributions of detector energy resolution, detector position
resolution and Doppler broadening, respectively. The total values of the threeestimated values are plotted by open circles.

Fig. 14. Compton reconstructed spectra of 22 Na (upper) and 137 Cs (lower).
The achieved energy resolutions are 13.8 keV and 18.0 keV for 511 keV and
662 keV gamma-rays, respectively.

In order to improve the quality of the Compton reconstruction
image, the arrangement of DSSD scatterers and CdTe absorbers
is important. Small scattering angles minimize the Doppler
broadening effect, which limits the angular resolution of the
prototype. In addition, a symmetric arrangement of CdTe absorbers is indispensable to obtain obtain undistorted images. On
the other hand, for the higher energy resolution, it is essential
to improve the energy resolution of CdTe absorbers. Based on
the results, we are developing the next prototype, consisting of
more DSSD layers and a symmetrical arrangement of CdTe
absorbers. We are also addressing further improvements of
CdTe detectors to achieve a high energy resolution.
ACKNOWLEDGMENT
The authors would like to thank C. Baluta for his criticalreading of the manuscript.
Fig. 13. Compton reconstructed spectra of 133 Ba. The dashed line shows
the simple sum of two-hit events, while the solid line shows the sum of events
identified to be emitted from the source by Compton reconstruction. The energy
resolution is 9.1 keV (FWHM) at 356 keV.

required to achieve a < 1% energy resolution [25]. In order toenable such a high bias voltage, improvements in bump bonding
and electrode formations are essential.
IV. S UMMARY AND F URTHER P ROSPECTIVE
We have constructed a prototype Si/CdTe Compton camera,
consisting of six-layered DSSDs and three 8 × 8 CdTe pixel
detectors. By using this prototype, we have obtained Compton
reconstructed images and spectra of gamma-rays from 122 keV
to 662 keV. The achieved energy resolutions are 9.1 keV and14 keV at 356 keV and 511 keV, respectively. The angularresolution is 3.9 degree (FWHM) for 511 keV gamma-ray
photons.

R EFERENCES[1] T. Takahashi, K. Makishima, Y. Fukazawa, M. Kokubun, K. Nakazawa,
M. Nomachi, H. Tajima, M. Tashiro and Y. Terada, “Hard X-ray and γ-ray
Detectors for the NEXT mission”, New Astronomy Reviews, 48, pp. 269–
273, 2004.
[2] T. Takahashi, A. Awaki, T. Dotani, Y. Fukazawa, K. Hayashida, T. Kamae,
J. Kataoka, N. Kawai, S. Kitamoto, T. Kohmura, M. Kokubun, K. Koyama,
K. Makishima, H. Matsumoto, E. Miyata, T. Murakami, K. Nakazawa,
M. Nomachi, M. Ozaki, H. Tajima, M. Tashiro, T. Tamagawa, Y. Terada,
H. Tsunemi, T. Tsuru, K. Yamaoka, D. Yonetoku, and A. Yoshida, “Wideband X-ray Imager (WXI) and Soft Gamma-ray Detector (SGD) for the
NeXT Mission”, Proc. SPIE, 5488, pp. 549–560, 2004.
[3] T. Takahashi, K. Nakazawa, T. Kamae, H. Tajima, Y. Fukazawa, M. Nomachi and M. Kokubun, “High resolution CdTe detectors for the next generation multi-Compton gamma-ray telescope”, Proc. SPIE, 4851, pp. 1228–
1235, 2003.
[4] G. Kanbach, R. Andritschke, F. Schopper, V. Schönfelder, A. Zoglauer,
P.F. Bloser, S.D. Hunter, J.A. Ryan, M. McConnell, V. Reglero, G. DiCocco
and J. Knödlseder, “The MEGA project”, New Astronomy Reviews, 48,
pp. 275–280, 2004.
[5] J.D. Kurfess, W.N. Johnson, R.A. Kroeger, B.F. Phlips and E.A. Wulf,“Development and applications of position-sensitive solid-state gamma ray
detectors”, Nucl. Instrum. Methods, A505, pp. 256–264, 2003.

[6] T. J. O’Neill, D. Bhattacharya, M. Polsen, A.D. Zych, J. Samimi
and A. Akyuz, “Development of the TIGRE Compton telescope forintermediate-energy gamma-ray astronomy”, IEEE Trans. Nucl. Sci., vol.
50, pp. 251–257, 2003.
[7] Y.F. Du, Z. He, G.F. Knoll, D.K. Wehe and W. Li, “Evaluation of aCompton scattering camera using 3-D position sensitive CdZnTe detectors”, Nucl. Instrum. Methods, A457, pp. 203–211, 2001.
[8] T. Kamae, R. Enomoto and N. Hanada, “A new method to measure energy,
direction, ans polarization of gamma rays”, Nucl. Instrum. Methods, A260,
pp. 254–257, 1987.
[9] F. Lei, A.J. Dean and G.L. Hills, “Compton polarimetry in gamma-ray
astronomy”, Space Science Reviews, 82, pp. 309–388, 1997.
[10] T. Takahashi, T. Mitani, Y. Kobayashi, M. Kouda, G. Sato, S. Watanabe,
K. Nakazawa, Y. Okada, M. Funaki, R. Ohno and K. Mori, “High
Resolution Schottky CdTe Detector,” IEEE Trans. Nucl. Sci., vol. 49,
pp. 1297–1303, 2002.
[11] T. Tanaka, Y. Kobayashi, T. Mitani, K. Nakazawa, K. Oonuki, G. Sato,
T. Takahashi and S. Watanabe, “Recent achievements of the high resolution
Schottky CdTe diode for γ-ray detectors”, New Astronomy Reviews, 48,
pp. 309–313, 2004.
[12] K. Nakazawa, K. Oonuki, T. Tanaka, Y. Kobayashi, K. Tamura, T. Mitani,
G. Sato, S. Watanabe, T. Takahashi, R. Ohno, A. Kitajima, Y. Kuroda and
M. Onishi, “Improvement of the CdTe Diode Detectors using a Guard-ringElectrode”, IEEE Trans. Nucl. Sci., vol. 51, pp. 1881–1885, 2004.
[13] Y. Fukazawa, T. Nakamoto, N. Sawamoto, S. Uno, T. Ohsugi, H. Tajima,
T. Takahashi, T. Mitani, T. Tanaka and K. Nakazawa, “Low-noise Doublesided Silicon Strip Detector for Soft Gamma-ray Compton Camera”, Proc.
SPIE, 5501, 2004.
[14] H. Tajima, T. Kamae, S. Uno, T. Nakamoto, Y. Fukazawa, T. Mitani,
T. Takahashi, K. Nakazawa, Y. Okada and M. Nomachi, “Low Noise
Double-Sided Silicon Strip Detector for Multiple-Compton Gamma-ray
Telescope”, Proc. SPIE, 4851, pp. 875–884, 2003.
[15] R. Ribberfors, “Relationship of the relativistic Compton cross section to
the momentum distribution of bound electron states”, Phys. Rev. B, vol. 12,
pp. 2067–2073, 1975.
[16] T. Tanaka, T. Mitani, S. Watanabe, K. Nakazawa, K. Oonuki, G. Sato,
T. Takahashi, K. Tamura, H. Tajima, H. Nakamura, M. Nomachi,
T. Nakamoto and Y. Fukazawa, “Development of a Si/CdTe semiconductor
Compton telescope”, Proc. SPIE, 5501, pp. 229–240, 2004.
[17] T. Mitani, T. Tanaka, K. Nakazawa, T. Takahashi, H. Tajima, H. Nakamura, M. Nomachi, T. Nakamoto and Y. Fukazawa, “A Prototype of
Si/CdTe Compton Camera and the Polarization Measurement”, IEEE
Trans. Nucl. Sci., vol. 51, pp. 2432–2437, 2004.
[18] H. Tajima, T. Nakamoto, T. Tanaka, S. Uno, T. Mitani, E do Couto e Silva,
Y. Fukazawa, T. Kamae, G. Madejski, D. Marlow, K. Nakazawa, M. Nomachi, Y. Okada and T. Takahashi, “Performance of a Low Noise Front-end
ASIC for Si/CdTe Detectors in Compton Gamma-ray Telescope”, IEEE
Trans. Nucl. Sci., vol. 51, pp. 842–847, 2004.
[19] T. Takahashi, S. Watanabe, M. Kouda, G. Sato, S. Kubo, Y. Kuroda,
M. Onishi and R. Ohno, “High Resolution CdTe Detector and Applications
to Imaging Devices,” IEEE Trans. Nucl. Sci. vol. 48, No.3, pp. 281–291,
2001.
[20] M. Nomachi, S. Ishii, Y. Kuroda, H. Nakamura, T. Sugimoto and
T. Takahashi, “A Data Readout System with High-Speed Serial Data Link
for Balloonborne X-ray Detectors”, IEEE Trans. Nucl. Sci., submitted in
2004[21] T. Mitani, H. Nakamura, S. Uno, T. Takahashi, K. Nakazawa, S. Watanabe, H. Tajima, M. Nomachi, Y. Fukazawa, S. Kubo, Y. Kuroda, M. Onishi
and R. Ohno, “Large area Gamma-ray Imaging Detector Based on High
Resolution CdTe Diode”, IEEE Trans. Nucl. Sci., vol. 50, pp. 1048–1052,
2003.
[22] A. Zoglauer and G. Kanbach, “Doppler broadening as a lower limit to
the angular resolution of next generation Compton telescopes”, Proc SPIE,
4851, pp. 1302–1309, 2003.
[23] S. Agostinelli et al., “GEANT4– a simulation toolkit”, Nucl. Instrum.
Methods, A506, pp. 250–303, 2003.
[24] R.M. Kippen, “The GEANT low energy Compton scattering (GLECS)
package for use in simulating advanced Compton telescopes”, New Astronomy Reviews, 48, pp. 221–225, 2004.
[25] T. Takahashi and S. Watanabe, “Recent Progress in CdTe and CdZnTe
Detector,” IEEE Trans. Nucl. Sci., vol. 48, No. 4, pp. 950-959, 2001.