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Employing Fourier-synthesis optics and one-dimensional position-sensitive detectors, we are developing a novel hard X-ray imager which can work in the ~ 10 keV to ~ 200 keV range either as a telescope or a microscope. As the detection part of our imager, we have developed a strip detector made of Schottky CdTe diode, with its cathode divided into 64 channels of 150 [micro]m pitch. Electrodes of all channels are gold-stud bonded to a fanout board, and connected to low noise analog ASIC. We read out signals from all channels simultaneously. As the grid optics elements, one-dimensional 'modulation collimator' grids of 1 mm thick tungsten have been manufactured, with 10 grid pitches ranging from 0.2 mm to 2 mm with harmonic ratios. Combining the CdTe strip detector and the grids, we have verified hard X-ray imaging performance of this system. Using an [sup.241]Am source, we have successfully obtained an image in the 10-70 keV range with a spatial resolution of ~ 0.5 mm. Index Terms--CdTe, Fourier transforms, microstrip, X-ray astronomy detectors, X-ray imaging.

Compton telescopes based on semiconductor technologies are being developed to explore the gamma-ray universe in an energy band 0.1-20 MeV, which is not well covered by the present or near-future gamma-ray telescopes. The key feature of such Compton telescopes is the high energy resolution that is crucial for high angular resolution and high background rejection capability. The energy resolution around 1 keV is required to approach physical limit of the angular resolution due to Doppler broadening. We have developed a low noise front-end ASIC (application-specific integrated circuit), VA32TA, to realize this goal for the readout of double-sided silicon strip detector (DSSD) and cadmium telluride (CdTe) pixel detector which are essential elements of the semiconductor Compton telescope. We report on the design and test results of the VA32TA. We have reached an energy resolution of 1.3 keV [full-width at half-maximum (FWHM)] for 60 and 122 keV at 0[degrees] C with a DSSD and 1.7 keV (FWHM) with a CdTe detector. Index Terms--Analog integrated circuits, cadmium telluride, Compton camera, gamma-ray detectors, silicon radiation detectors.

We report the performance of an Avalanche Photodiode (APD) that has a large-area (1 cm²) and a thick depletion layer (~30 µm) in application to electron measurements. It is shown that the dead layer is sufficiently thin for the detection of electrons at energies less than 10 keV; the lowest measurable energy is ~5 keV. We also confirmed that the energy resolution is not significantly deteriorated by the non-uniformity of the thickness of the dead layer or the internal gain. The energy resolution at the lower energy range (<10 keV) is limited by the electric noise. Dependence of the electric noise on the detector size is also discussed. Furthermore, the effective multiplication profile in the normal direction is inferred from the experimental data. [ABSTRACT FROM AUTHOR]

Recent results from the Schottky CdTe diode detectors employing a guard-ring (GR) electrode are reported. A cathode electrode, made of platinum, was separated into an active electrode(s) and a surrounding GR. Typical leakage current of a device with active area of 2 × 2 mm² and 0.5 mm thickness surrounded by a GR, is 7 and 20 pA at a bias of 100 and 500 V, respectively, operated at 20 ° Spectral resolution of this device is 0.93 and 1.2 keV (FWHM) at 59.5 and 122 keY, respectively, operated at 20 °C with a bias of 800 V. Detailed study of the characteristics of these devices working as a gamma-ray detector is presented. [ABSTRACT FROM AUTHOR]

Deals with a study which developed a large array detector composed of 1024 individual CdTe diodes. Schottky CdTe diode under edge-on geometry; Large area gamma-ray camera; Readout electronics.

Describes progress on the use of Schottky cadmium telluride (CdTe) diode detectors for spectrometry. Advantage from the low leakage current of the CdTe diode; Implication of the high bias voltage for a relatively thin detector; Factors that lead to an energy resolution.

Presents a study that developed a method to extract mobility-lifetime products in order to characterize cadmium telluride/cadmium zinc telluride detectors in a planar configuration. Characteristics of the detectors; Way of determining mobility; Issues for a detector to be used as a spectrometer.

We describe the recent progress on the use of Schottky Cadmium telluride (CdTe) diode detectors for γ-ray spectroscopy. The extremely low leakage current of the newly developed CdTe diode allows us to apply a much higher bias voltage in comparison with the previous CdTe detectors. Both the improved charge-collection efficiency and the low leakage current lead to a good energy resolution even at room temperature. Large-area CdTe diode detectors with dimensions of 21.5 × 21.5 mm2 are now available. By stacking 40 layers of these large-area devices, we have achieved a good energy resolution of several keV (FWHM) for MeV γ-rays. [Copyright &y& Elsevier]

Abstract: We are developing a semiconductor Compton telescope to explore the universe in the energy band from several tens of keV to a few MeV. A detector material of combined Si strip and CdTe pixel is used to cover the energy range around 60keV. For energies above several hundred keV, in contrast, the higher detection efficiency of CdTe semiconductor in comparison with Si is expected to play an important role as both an absorber and a scatterer. In order to demonstrate the spectral and imaging capability of a CdTe-based Compton camera, we developed a Compton telescope consisting of a stack of CdTe pixel detectors as a small scale prototype. With this prototype, we succeeded in reconstructing images and spectra by solving the Compton kinematics within the energy band from 122 to 662keV. The energy resolution (FWHM) of reconstructed spectra is 7.3keV at 511keV. The angular resolution obtained at 511keV is measured to be (FWHM). [Copyright &y& Elsevier]

Abstract: We are developing a Compton telescope based on high-resolution Si and CdTe detectors for astrophysical observations in sub-MeV/MeV gamma-ray region. Recently, we constructed a prototype Compton telescope which consists of six layers of double-sided Si strip detectors (DSSDs) and CdTe pixel detectors to demonstrate the basic performance of this new technology. By irradiating the detector with gamma rays from radio isotope sources, we have succeeded in Compton reconstruction of images and spectra. The obtained angular resolution is 3.9°(FWHM) at 511keV, and the energy resolution is 14keV (FWHM) at the same energy. In addition to the conventional Compton reconstruction, i.e., drawing cones in the sky, we also demonstrated a full reconstruction by tracking Compton recoil electrons using the signals detected in successive Si layers. By irradiating 137Cs source, we successfully obtained an image and a spectrum of 662keV line emission with this method. As a next step, development of larger DSSDs with a size of is under way to improve the effective area of the Compton telescope. We are also developing a new low-noise analog ASIC to handle the increasing number of channels. Initial results from these two new technologies are presented in this paper as well. [Copyright &y& Elsevier]

Abstract: We report our development of CdTe pixel detectors for Si/CdTe semiconductor Compton cameras. We have constructed a prototype of a Si/CdTe Compton camera, consisting of six layered double-sided silicon strip detectors and three CdTe pixel detectors. By using this prototype, we have demonstrated the concept of the Si/CdTe Compton cameras. We have successfully obtained Compton reconstructed images for 80–662keV gamma-rays. The achieved angular resolution is about 4degrees for 511keV gamma-rays. The energy resolution is 14keV (FWHM) at 511keV. In order to improve the performance of the Compton camera, we have evaluated all CdTe pixel detectors we have constructed. We found that the – curve is helpful to select good detectors. [Copyright &y& Elsevier]

Abstract: Cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) have been regarded as promising semiconductor materials for hard X-ray and -ray detection. The high-atomic number of the materials gives a high quantum efficiency in comparison with Si. The large band-gap energy allows to operate the detector at room temperature. Based on recent achievements in high-resolution CdTe detectors, in the technology of ASICs and in bump-bonding, we have proposed the novel hard X-ray and -ray detectors for the NeXT mission in Japan. The high-energy response of the super mirror onboard NeXT will enable us to perform the first sensitive imaging observations up to 80keV. The focal plane detector, which combines a fully depleted X-ray CCD and a pixellated CdTe detector, will provide spectra and images in the wide energy range from 0.5 to 80keV. In the soft -ray band up to , a narrow field-of-view Compton -ray telescope utilizing several tens of layers of thin Si or CdTe detector will provide precise spectra with much higher sensitivity than present instruments. The continuum sensitivity will reach several in the hard X-ray region and a few in the soft -ray region. [Copyright &y& Elsevier]