Development of a Si/CdTe semiconductor Compton telescope
Takaaki Tanakaa,b , Takefumi Mitania,b , Shin Watanabea , Kazuhiro Nakazawaa ,Kousuke Oonukia,b , Goro Satoa,b , Tadayuki Takahashia,b ,Ken’ichi Tamuraa,b , Hiroyasu Tajimac , Hidehito Nakamurad , Masaharu Nomachid ,Tatsuya Nakamotoe and Yasushi Fukazawaea Institute of Space and Astronautical Science, JAXA, Sagamihara, Kanagawa, 229-8510,

Japan

b Department of Physics, University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japanc Stanford Linear Accelerator Center, Stanford, CA 94309-4349, USAd Department of Physics, Osaka University, Toyonaka, Osaka, 560-0043, Japane Department of Physics, Hiroshima University, Higashi-Hiroshima, Hiroshima, 739-8526,

Japan
ABSTRACT
We are developing a Compton telescope based on high resolution Si and CdTe imaging devices in order to obtaina high sensitivity astrophysical observation in sub-MeV gamma-ray region. In this paper, recent results fromthe prototype Si/CdTe semiconductor Compton telescope are reported. The Compton telescope consists of adouble-sided Si strip detector (DSSD) and CdTe pixel detectors, combined with low noise analog LSI, VA32TA.
With this detector, we obtained Compton reconstructed images and spectra from line gamma-rays ranging from
81 keV up to 356 keV. The energy resolution is 3.8 keV and 7.9 keV at 122 keV and 356 keV, respectively, andthe angular resolution is 9.9◦ and 5.7◦ at 122 keV and 356 keV, respectively.
Keywords: gamma-ray, Compton telescope, semicondictor detector, CdTe, Silicon Strip Detector

1. INTRODUCTION
Gamma-ray universe in the energy band of 100 keV to 10 MeV is a good observational window to study nucleosynthesis and particle acceleration in high energy astrophysical objects. However, in this energy band, observation
sensitivity have been still limited, due to high background, difficulty in detecting photons, and incapability ofimaging. A Compton telescope tracking the Compton scattering process of gamma-rays by position and energy
sensitive detectors is difficult but a promising approach to bring a breakthrough in this energy band.
In the MeV region, COMPTEL1 on-board CGRO (Compton Gamma-Ray Observatory) was the first successfulCompton telescope and brought many pioneering results.2 In a Compton telescope, deposited energy andposition of the gamma-ray interactions with the detector are acquired. When a gamma-ray photon is scatteredin one detector and absorbed in another detector, the incident energy of the gamma-ray and the scattering angle
can be determined as,
Ein
cos θ

= E1 + E2
me c2
me c2
= 1−
+
,
E2
E1 + E2(1)(2)

where E1 is the energy of the recoil electron, E2 is the energy of the scattered photon and θ is the scattering
angle. The latter equation presents the incident direction as a cone in the sky.
As shown in equation (2), incident direction of a gamma-ray is calculated from the position and the energy
information of interactions. Therefore, employing semiconductor imaging spectrometers as components of Compton telescopes, with their good energy and position resolution, will drastically improve the angular resolution
Further author information: (Send correspondence to T.Tanaka) E-mail: ttanaka@astro.isas.jaxa.jp

and hence the sensitivity. In this point of view, advanced Compton telescopes based on Si, Ge, CZT and CdTe
are proposed and development is on-going in many groups.3–8 A Compton telescope also enables us to measurepolarization of gamma-rays, by obtaining the azimuthal distribution of Compton scattering.9, 10
Based on our CdTe and Si detector technologies,11–15 we are working on a new Si/CdTe semiconductor
Compton telescope to explore the universe in the energy band from 100 keV to a few MeV. In this paper,
we describe experimental results obtained with a prototype Compton telescope which consists of one layer ofa Double-sided Si strip detector (DSSD) and one layer of CdTe pixel detectors. Detailed performance of the
DSSD and the vision of next-generation gamma-ray missions using this technique are reported elsewhere in thisconference proceedings.14, 16 Demonstration of polarization detection are reported in Mitani et al.17 and Tajima
et al.18

2. SI/CDTE SEMICONDUCTOR COMPTON TELESCOPE
Basic concept of Si/CdTe Compton telescope is to utilize Si as a scatterer and CdTe as an absorber.4, 17 Compared to Compton telescopes using scintillator as an absorber, this design improves the performance especially at
sub-MeV region, as low as 100 keV. The lower energy coverage is prefered to connect the band pass of Compton
telescope with that of the technology using hard X-ray focusing mirror optics.19, 20
A schematic image of Si/CdTe Compton telescope is shown in Figure 1. The major interaction processof Si with gamma-rays with energy higher than 60 keV is Compton scattering, while in CdTe photo-electric
absorbtion is still dominant up to 300 keV (Figure 2). In a Si/CdTe Compton telescope, therefore, “oneCompton and absorption” events dominate the data around several hundred keV. A merit of utilizing this kindof event is that it is relatively easy to analyze. For example, in Compton scattering of photons with energy lessthan me /2 = 255.5 keV, the recoil electron energy is always less than that of the scattered photon.3 In addition,
the ambiguity in the Compton scattering angle caused by the orbital motion of bound electron is relatively small
for Si compared to that of Ge and CdTe. This effect is called “Doppler broadening effect21 ”, and is the dominantfactor of angular resolution around a few hundered keV.
The demerit of current Si/CdTe Compton telescope design is that it looses effective area especially at thehigher energy band, as much as a few MeV. This is simply because the density of Si (2.3 g/cm3 ) is much less thanthat of CdTe (5.9 g/cm3 ). For Compton telescope aiming mainly at a few MeV band, increasing the number
and thickness of CdTe layers becomes important.
Ein
Si

θ
E1
CdTe
E2
Figure 1. Schematic picture of our Si/CdTe semiconductor Compton telescope under development

3. EXPERIMENTAL SETUP
Two key technologies for our Si/CdTe Compton telescope are DSSD and CdTe pixel detectors. In this section,
we describe the detail of the newly developed 8 × 8 CdTe pixel detector and design of the prototype Compton

Figure 2. Linear attenuation coefficients for photo-electric absorption, Compton scattering and pair production in Si
and CdTe.

telescope. Detail of the DSSD development is described in Fukazawa et al.,14 this conference.

3.1. The 8 × 8 CdTe Pixel Detector
The 8 × 8 CdTe pixel detector is based on the Schottky CdTe diode device, utilizing indium as the anode andplatinum as the cathode. This device is developed with ACRORAD, Japan and characterized by its low leakage
current and high uniformity.11, 22 Figure 3 (left) shows the photo of the detector. The detector has dimensionsof 18.55 mm × 18.55 mm and a thickness of 500 µm. The indium side is used as a common electrode and theplatinum side is divided into 8 by 8 pixels and a guard ring with a width of 1 mm. The guard-ring electrodeare attached to reduce the leakage current of the side and corner pixels because most of the leakage current isthrough the detector perimeter.12, 13 Pixel size is 2 mm × 2 mm, and the gap between each pixel is 50 µm.
Each pixel is connected to a fanout board by bump bonding technology developed in cooperation with
Mitsubishi Heavy Industry, Japan.23 Since the leakage current of each pixel is as low as ∼ 100 pA at a bias
voltage of 500 V even at room temperature, the signal lines are directly connected to the input of readout
electronics, an analog LSI VA32TA.15, 24 This LSI is developed with IDEA, Norway, and characterized by its
low noise. The LSIs are read out via specially designed compact readout system including an ADC and FPGA,
which is controlled with a fast serial interface ”Space Wire (IEEE 1355)”.25
Figure 3 (right) shows a spectrum of 57 Co obtained with the CdTe pixel detectors employed in the prototype
Compton telescope. In these detectors, all 128 channels are properly connected and their spectra are summed
after gain correction. The data is measured at a temperature of −10 ◦ C and with a bias voltage of 500 V. Theenergy resolution is 3.2 keV (FWHM) for the 122 keV peak.

3.2. The prototype Compton Telescope System
The prototype Si/CdTe Compton telescope consists of two CdTe pixel detectors and a DSSD. The DSSD has
a thickness of 300 µm. There are 64 strips with a length of 2.53 cm in both sides oriented orthogonally. The
strip pitch is 400 µm and the gap between the strips is 100 µm. By reading out both the p-strips and n-strips,
we can obtain two-dimensional positional information. The device is also read out with VA32TA. The p-strips
are connected directly to the input of the LSI, and the n-strips are connected via coupling capacitors. To fully
deplete the device, the n-side is biased with a voltage of 110 V. Because the spectral resolution of the p-side isbetter than that of the n-side, we obtained spectra only from the p-strips, and data from the n-strips are used forthe positional information. Figure 4 shows a spectrum of 133 Ba obtained with the p-strips of the DSSD operated
at a temperature of −10 ◦ C. The energy resolution for 81.0 keV peak is 1.9 keV (FWHM).

Figure 3. Photo of the 8 × 8 CdTe pixel detector (left) and 57 Co spectrum from all 128 channels with the two detectors
employed in the prototype Compton telescope(right). The operated temperature is −10 ◦ C and the applied bias voltage
is 500 V. The peaking time of the shaping amplifier in VA32TA is set at 2 µsec.

Figure 5 presents the arrangement of two CdTe pixel detectors and the DSSD at our Compton telescope.
The separation between the DSSD layer and the CdTe layer is 12.5 mm. In the following experiment, we kept
the whole detector system at a temperature of −10 ◦ C. We irradiated gamma-ray sources of 57 Co and 133 Ba
which were placed 353 mm above the surface of the DSSD. Triggers only from the LSIs connected to the CdTe
detectors were enabled. When a trigger was generated from some channel, all channels connected to the CdTe
detector which issued the trigger and all channels connected to the DSSD are read out.

Figure 4. Photo of the DSSD (left) and 133 Ba spectrum obtained with the p-strips at a temperature of −10 ◦ C (right).
The peaking time of the shaping amplifier is 2 µsec.

CdTe
Pixel
(No.1)

DSSD
ch 31

DSSD
CdTe
Pixel
(No.2)yp−sidexz1.25 cmp−siden−sideCdTe Pixel(No.2)
z

CdTe Pixel(No.1)ch 0
ch 31

n−sidech 0yx

Figure 5. Configuration of the prototype Si/CdTe Compton telescope.

4. DATA ANALYSIS
4.1. Compton Reconstruction of Images
Data reduction is performed as follows. First,“two-hit events”, one hit in DSSD and one hit in CdTe, wereselected from the raw data. Here, one hit in DSSD means that only one channel that is connected to DSSD has
a pulse hight above 6 keV, and one hit in CdTe detectors means that only one channel that is connected to CdTe
detectors has a pulse hight above 20 keV.
A scatter plot of the energy deposit at the DSSD (ESi ) and at the CdTe detectors (ECdTe ) is shown in Figure 6.
This plot is obtained when we irradiated 57 Co to the Compton telescope. There are branches which satisfies
ESi + ECdTe ∼= 122 keV and ESi + ECdTe ∼= 136 keV. These branches are the events in which incident gamma-raysof 122 keV or136 keV are scattered in one detector and then absorbed in the other. Another noticeable branches
are those parallel to the horizontal axis around ESi = 20–30 keV. These are the events by the fuorescence X-rays
from Cd (Kα : 23.1 keV, Kβ : 26.1 keV) and Te (Kα : 27.4 keV, Kβ : 31.0 keV) which escape from the CdTe
detectors and are absorbed in the DSSD, and not the Compton events.
For these “two-hit events”, we calculated the Compton-scattering angle by using equation (2). In the calculation, we assumed that incident gamma-rays are scattered in the DSSD and absorbed in the CdTe pixel detector.
From the calculated scattering angle and the two hit positions, the Compton cones are drawn on the sky event by
event. We projected the cone at the plane at the distance of 353 mm, and obtained the image of the gamma-ray
source. Figure 7 shows the images obtained with the experimental data, in which the gamma-ray source position
can be clearly identified.
Figure 7(a) is obtained by irradiating gamma-rays from two 57 Co sources. These sources are placed 230 mm
separate from each other, which corresponds to 33◦ at the distance of 363 mm. The 57 Co image is obtained by
selecting events in which sum of the energy deposit at the DSSD and the CdTe detectro is within 122 ± 5 keV.
For the 133 Ba images, energy selection is above 250 keV and 81 ± 5 keV for Figure 7(b) and (c), respectively.
In Figure 7, appearance of each image is different. This reflects the basic process and geometry of the detector.
For example, 81 keV image has a peculiar “batterfly-like” shape. This is caused by the fact that the scattering
angle must be larger than 60◦ to deposit an energy larger than 6 keV at the DSSD, which is the energy thresholdin this analysis, and that Compton cones with peculiar orientation are obtained because the CdTe detectors areoffset from the DSSD. Another impressive image is obtained when we select the energy band of 100–250 keV for133
Ba irradiation data (Figure 7(d)). Compared with line images (Figure 7(b) and (c)), the location of 133 Ba

Figure 6. Scatter plot of deposited energy at the DSSD (ESi ) and at the CdTe detectors (ECdTe ) for all two-hit events
when we irradiated 57 Co to the prototype detector.

source is not clear. This is because the image is dominated by back scattered events and “Compton-Compton”
events which finally escaped from the detector. From this data, we see that it is better to use thicker CdTe
detector and, if possible, utilize a surrounding shield counter to identify the physical process of each event.

4.2. Angular Resolution
In order to evaluate angular resolution of our prototype Compton telescope, we compare the calculated Comptonscattering angles (θComp ) with those defined by the location of gamma-ray source and hit positions (θGeom ) (seeFigure 8). The difference between the two values reflects the angular resolution of Compton telescope.
We examined the distribution of θComp − θGeom for various peaks of 57 Co (122 keV and 136 keV) andBa (81.0 keV, 303 keV and 356 keV). Figure 9 shows the example of 122 keV events. The FWHM of these
distributions (∆θexp ), which is the angular resolution of the Compton telescope, is plotted against the incident
gamma-ray energy in Figure 10. The angular resolution obtained from Geant4 Monte Carlo simulations,26 using
the Compton scattering process, G4LECS27, 28 are also plotted. The experimental results are consistent with theresults from the simulation.
133

As shown in Figure 10, the angular resolution becomes better as the incident gamma-ray energy becomes
higher. For example, ∆θexp = 16◦ at 81.0 keV and ∆θexp = 5.7◦ at 356 keV. In order to examine the reasonof this tendency, we estimated the contribution of position and energy resolution of the DSSD and the CdTe
detector. Contribution of position resolution (∆θpos ) is estimated by using the actual hit positions obtained
from the experiment and the strip/pixel size of the DSSD and the CdTe detector. To estimate the contributionof energy resolution (∆θene ), we used the Compton-scattering angles of actual events and smoothed them with
detector energy resolution. In Figure 10, the estimated values are plotted. In the same Figure, the values ofq∆θDB = (∆θexp )2 − (∆θpos )2 − (∆θene )2(3)
are also plotted. This can be interpreted to be the contribution of Doppler broadening, which is supportedby the fact that the experimental data is consistent with those obtained from simulations. As seen in Figure
10, ∆θene and ∆θDB becomes smaller as the incident energy becomes higher, whereas ∆θpos becomes larger.
The tendency of ∆θDB is consistent with that of Monte Carlo simulations in several papers (e.g. Zoglauer andKanbach 200321 ). ∆θpos becomes smaller when the incident gamma-ray energy is smaller, because in such events

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Figure 7. Compton reconstructed images. (a) Image of two 57 Co sources by events within 122 ± 5 keV. (b)–(d) Imageobtained by irradiating 133 Ba. (b) Events in which total energy deposit is above 250 keV. (c) Events within 81 ± 5 keV.
(d) Events from 100 keV to 250 keV.

only larger scattering angle and hence the longer distance events can be reconstructed due to the energy thresholdfor the DSSD (6 keV).
In order to investigate the relation between the scattering angles and the angular resolution, we plotted
the angular resolution against Compton scattering angle from 57 Co data in Figure 11. The estimated value of
uncertainty due to position resolution, energy resolution and Doppler broadening are obtained in the same way
as Figure 10 and plotted together. The value of ∆θexp is somewhat larger for larger scattering angles, and ouranalysis shows that this tendency is caused by Doppler broadening. In other words, the contribution of Doppler
broadening can be reduced if we can reconstruct the events with smaller scattering angles, which means lower
energy threshold for the DSSD.

Position of the Source(known)

γ
θGeom
DSSD

CdTe pixel

Figure 8. Definition of θGeom

Figure 9. Distribution of θComp − θGeom for 122 keV events.

Figure 10. Relation between incident gamma-ray energy and angular resolution.

Figure 11. Relation between Compton-scattering angle and angular resolution for 122 keV events.

4.3. Compton Reconstruction of Spectra
Energy spectra of the incident gamma-rays are obtained by summing deposited energy at the DSSD and the
CdTe detector as shown in equation (1). The dotted lines in Figure 12 show the spectra which we obtained bysimply summing the deposited energy at each detector for all “two-hit events”. In these spectra, the gamma-ray
peaks from the sources can not be clearly identified since we can not distinguish “one-Compton and absorption
events” from other “two-hit events”, such as events in which gamma-rays are scattered in the DSSD and scatteredagain in the CdTe and so on. Then we performed event selection by Compton kinematics. We selected the events
satisfying |θComp − θGeom | < 16◦ . The solid lines in Figure 12 show the spectra of gamma-rays from 57 Co and133
Ba after this selection. In these spectra, the gamma-ray peaks from the source are relatively enhanced.
The energy resolution is 3.8 keV (FWHM) for 122 keV gamma-rays and 7.6 keV for 356 keV. These values
are generally consistent with the energy resolution of the DSSD (1.9 keV) and the CdTe pixel detectors (3.2 keV
for 122 keV and 7.5 keV for 356 keV) under this setup, i.e. the energy resolution of this Compton telescope isexpressed asp∆E = (∆ESi )2 + (∆ECdTe )2 ,(4)
where ∆ESi and ∆ECdTe are the energy resolution of the DSSD and the CdTe detector, respectively.

4.4. Compton Reconstruction of K-escape Events
As described above, significant number of fluorescence X-rays from the CdTe detectors are detected in the DSSD
due to high fluorescence yield of Cd and Te (∼ 80% for the K shell). Depending on the detector geometry,K-escape events can share significant ratio in total events. Therefore, we attempted to reconstruct events inwhich photons are scattered at the DSSD, absorbed at the CdTe, K-escape takes place and the fluorescence line
is detected again in the DSSD.
First, we selected three-hit events, twice in the DSSD and once in the CdTe detector. Then we further selectthe events in which one of the deposited energy in the DSSD is between 20 keV and 34 keV. After adding thesemeasured value to the energy observed in the CdTe detector, we calculated the Compton-scattering angle as theusual two-hit events. Figure 13 (right) shows a spectrum of 57 Co obtained from this analysis. Only the events
which satisfy |θComp − θGeom | < 16◦ are selected. The peak around 122 keV is clearly identified.

Figure 12. Compton reconstructed spectra of 57 Co (left) and 133 Ba (right). Dotted lines show the simple sum of two-hit
events, while solid lines show the sum of events identified to be emitted from the source by Compton reconstruction.
Note that there are many events which are photo-absorbed in CdTe followed by K-escape emission in the former, whichis excluded in the latter, so that the peak counts also becomes smaller in the latter.

γ

Compton scattering

Photo−electric absorption

DSSD

fluorescence X−ray

CdTe pixel
Photo−electric absorption

Figure 13. Three-hit events by K-escape (left) and the reconstructed spectrum of 57 Co obtained from such events (right).

5. IMPLICATIONS FROM THE PROTOTYPE
From §4.2, it is clear that the angular resolution of the prototype Compton telescope can be improved if theenergy resolution becomes better especially for lower energy and if the position resolution becomes better for
higher energy. In view of energy resolution, the CdTe detectors used in the prototype Compton telescope are
not satisfactory. Actually, the best channel in other detector with the same design shows an energy resolution of
1.7 keV. We are currently trying to improve this properties by optimizing parameters for bump bonding. Figure
14 shows the sum spectrum of all channels of the latest version of 8 × 8 CdTe pixel device, obtained at 20 ◦ Cwith a bias voltage of 600 V. An energy resolution of 2.4 keV (FWHM) at 122 keV is obtained with the detector.
Development of CdTe pixel detectors with smaller pixel size is also in underway.29 If we can make the pixel size
smaller, we will improve not only the position resolution but also the energy resolution since the capacitance andthe leakage current per pixel can be reduced. However, we need to be careful for charge sharing or K-escape tothe other pixels in smaller pixel size detectors.
Obtaining higher detection efficiency is another crucial issue for the next version of the Compton telescope.
Currently, we are working on two directions. One is to make a multi-layer DSSD, up to 24 layers or more.
Another way is to improve the thickness of the detector. We are now developing 500 µm thick DSSD and thicker
CdTe pixel detectors up to 5 mm.

Figure 14. 57 Co spectrum obtained with our latest version of the 8×8 CdTe pixel detector operated at room temperature.
The applied bias voltage is 600 V.

6. CONCLUSION
Si/CdTe semiconductor Compton telescope is attractive to explore the universe in sub-MeV gamma-ray region.
We constructed a prototype Compton telescope which consists of one layer of DSSD and one layer of CdTe pixel
detectors. With this prototype detector, we succeeded in Compton reconstruction of images and spectra in theenergy band from 80 keV to 400 keV. The obtained angular resolution is 5.7◦ and 9.9◦ at 122 keV and 356 keV,
respectively, and the energy resolution is 3.6 keV (FWHM) at 122 keV and 7.6 keV (FWHM) at 356 keV.
The lower energy coverage down to 80 keV owes to good energy resolution and lower energy threshold of ourdetectors. We also succeeded in reconstruction of three-hit events by Compton scattering and K-escape, whichbecomes significant under some configuration of Compton telescopes. With these results, we have experimentallydemonstrated the high capabilities of a Si/CdTe Compton telescope.

REFERENCES
1. V. Schönfelder et al., “Instrument description and performance of the imaging gamma-ray telescope COMPTEL aboard NASA’s Compton Gamma Ray Observatory”, ApJ Suppl., 86, pp. 657–692, 1993.

2. V. Schönfelder et al., “COMPTEL overview: Achievements and expectations”, Astron. Astrophys. Suppl.,
120, pp. 13–21, 1996.
3. T. Takahashi et al., “Hard X-ray and γ-ray Detectors for the NEXT mission”, New Astronomy Reviews, 48,
pp. 269–273, 2004.
4. T. Takahashi et al., “High resolution CdTe detectors for the next generation multi-Compton gamma-ray
telescope”, Proc. SPIE, 4851, pp. 1228–1235, 2003.
5. G. Kanbach et al., “The MEGA project,” New Astronomy Reviews, 48, pp. 275–280, 2004.
6. J. D. Kurfess et al., “Development and applications of position-sensitive solid-state gamma ray detectors ,”Nucl. Instrum. Methods, A505, pp. 256–264, 2003.
7. T. J. O’Neill et al., “Development of the TIGRE Compton telescope for intermediate-energy gamma-ray
astronomy,” IEEE Trans. Nucl. Sci., 50, pp. 251–257, 2003.
8. Y. F. Du et al., “Evaluation of a Compton scattering camera using 3-D position sensitive CdZnTe detectors,”in Proc. SPIE, 3768, 1999, pp. 228–238.
9. 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.
10. F. Lei, A. J. Dean and G. L. Hills, “Compton polarimetry in gamma-ray astronomy,” Space Science Reviews,
82, pp. 309–388, 1997.
11. T. Takahashi et al., “ High Resolution Schottky CdTe Diodes”, IEEE Trans.Nucl. Sci., 49, pp. 1297–1303,
2002.
12. T. Tanaka et al., “Recent achievements of the high resolution Schottky CdTe diode for γ-ray detectors”,
New Astronomy Reviews, 48, pp. 309–313, 2004.
13. K. Nakazawa et al., “Improvement of the CdTe Diode Detectors using a Guard-ring Electrode”, IEEE Trans.
Nucl. Sci., in press, 2004.
14. Y. Fukazawa et al., “Low-noise Double-sided Silicon Strip Detector for Soft Gamma-ray Compton Camera”,
in this proceedings.
15. H. Tajima et al., “Low Noise Double-Sided Silicon Strip Detector for Multiple-Compton Gamma-ray Telescope”, Proc. SPIE, 4851, pp. 875–884, 2003.
16. T. Takahashi et al., “Wide-band X-ray imager (WHI) and soft gamma-ray detector (SGD) for the NEXTmission”, Proc. SPIE, 5488, 2004.
17. T. Mitani et al., “A Prototype of Si/CdTe Compton Camera and the Polarization Measurement”, IEEE
Trans. Nucl. Sci., in press, 2004.
18. H. Tajima et al., “Gamma-ray polarimetry with Compton Telescope”, Proc. SPIE, 5488, 2004.
19. K. Yamashita et al., “Supermirror hard-x-ray telescope”, Applied Optics, 37, pp. 8067–8073, 1998.
20. J. E. Koglin et al., “Development and production of hard X-ray multilayer optics for HEFT”, Proc. SPIE,
4851, pp. 607–618, 2002.
21. 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.
22. K. Nakazawa et al., “Large area CdTe diode detector for space application”, Nucl. Instrum. Methods, A512,
pp. 412–418, 2003.
23. T. Takahashi et al. “ High Resolution CdTe Detectorand Applications to Imaging Devices”, IEEE Trans.
Nucl. Sci., 48, pp. 287-291, 2001.
24. H. Tajima et al., “Performance of a Low Noise Front-end ASIC for Si/CdTe Detectors in Compton Gammaray Telescope”, IEEE Trans. Nucl. Sci., in press, 2004.
25. T. Mitani et al., “Large area Gamma-ray Imaging Detector Based on High Resolution CdTe Diode”, IEEE
Trans. Nucl. Sci., 50, pp. 1048–1052, 2003.
26. Geant4, http://wwwasd.web.cern.ch/wwwasd/geant4/geant4.html
27. R. M. Kippen, “The GEANT Low Energy Compton Scattering (GLECS) Packages for use in Simulating
Advenced Compton Telescopes”, New Astronomy Reviews, 48, pp. 221–225, 2004.
28. GEANT4 Low-Energy Compton Scattering (G4LECS) package, http://nis-www.lanl.gov/˜mkippen/actsim/
29. K. Oonuki et al., “Development of Uniform CdTe Pixel Detectors Based on Caltech ASIC”, in this proceedings.