We have been developed Si/CdTe semiconductor Compton telescope to explore the universe in the energy band from several 10 keV to a few MeV. In our Si/CdTe Compton telescope, a stacked thin CdTe pixel detector is a key component to achieve higher detection effciency for MeV gamma-rays maintaining high energy resolution. In this paper, results from a prototype stacked CdTe pixel detector are reported, which consists of three layers of CdTe pixel detectors and one CdTe pixel detector at their side. With this prototype detector, we succeeded in Compton reconstruction of images and spectra in the energy band from 122 keV to 662 keV. The energy resolution (FWHM) of reconstructed spectra is 7.3 keV at 511 keV and 3.1 keV at 122 keV, respectively.
Compton telescope is a promising technology to achieve very high sensitivity in the soft gamma-ray band (0.1-10 MeV) by utilizing Compton kinematics. Compton kinematics also enables polarization measurement which will open new windows to study gamma-ray production mechanism in the universe.
CdTe and Si semiconductor technologies are key technologies to realize the Compton telescope in which their high energy resolution is crucial for high angular resolution and background rejection capability. We have assembled a prototype module using a double-sided silicon strip detector and CdTe pixel detectors.
In this paper, we present expected polarization performance of a proposed mission (NeXT/SGD).
We also report results from polarization measurements using polarized synchrotron light and validation of EGS4 MC simulation.
We have developed a large CdTe pixel detector with dimensions of 23.7 x 13.0 mm2 and a pixel size of 448 x 448 μm2. The detector is based on recent technologies of an uniform CdTe single crystal, a two-dimensional ASIC, and stud bump-bonding to connect pixel electrodes on the CdTe surface to the ASIC. Good spectra are obtained from 1051 pixels out of total 1056 pixels. When we operate the detector at -50°C, the energy resolution is 0.67 keV and 0.99 keV at 14 keV and 60 keV, respectively. Week-long stability of the detector is confirmed at operating temperatures of both -50°C and -20°C. The detector also shows high uniformity: the peak positions for all pixels agree to within 0.82%, and the average of the energy resolution is 1.04 keV at a temperature of -50°C. When we normalized the peak area by the total counts detected by each pixel, a variation of 2.1% is obtained.
The Hard X-ray Detector (HXD-II), one of instruments onboard the Astro-E2 satellite to be launched in February 2005, is in the final stage of its development. The HXD-II probes the universe in the energy range of 10-600 keV with a sensitivity by an order of magnitude better than those of previous missions. The assembly of the HXD-II completed in January 2004, followed by a series of pre-launch qualification tests. As a result, the design goals of the HXD-II have been met. These include; a background level of 5 x 10-6 counts/s/keV/cm2 at 200 keV for GSO and 1 x 10-5 counts/s/keV/cm2 at 30 keV for PIN; energy resolutions of 2.9 keV (PIN diode, at 59.5 keV) and 10% (GSO scintillator, at 662 keV); and low energy thresholds of 10 keV for PIN diodes and 30 keV for GSO scintillators. The measured background predicts a continuum sensitivity of a few x 10-6 photons/s/keV/cm2. Anti-Counter units surrounding the HXD-II provide 50 keV-5 MeV information on gamma-ray bursts and bright X-ray transients.
A Semiconductor Multiple-Compton Telescope (SMCT) is expected to proceed a high-sensitivity soft gamma-ray observation in the energy range of 0.1-20 MeV. Double-sided silicon strip detector (DSSD) is one of key technologies for constructing SMCT, as well as the high-stopping semiconductor CdTe, because of its high energy resolution and high scattering efficiency. We have developed a low-noise system of DSSD and frontend LSI for SMCT, by optimizing geometrical structures of DSSD. We have thus obtained an energy resolution of 1.3 keV (FWHM) for 60 keV and 122 keV at -10°C in the multi-channel reading. Gamma-ray responses such as image flatness and charge splittings were found to be not problematic. We also demonstrated that our system achieved the good angular resolution close to the Doppler-broadening limit in the Compton imaging by two DSSDs.
We are developing a Compton telescope based on high resolution Si and CdTe imaging devices in order to obtain a high sensitivity astrophysical observation in sub-MeV gamma-ray region. In this paper, recent results from the prototype Si/CdTe semiconductor Compton telescope are reported. The Compton telescope consists of a double-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, and the angular resolution is 9.9° and 5.7° at 122 keV and 356 keV, respectively.