Cadmium Zinc Telluride (CZT) is the detector material of choice for the detection of X-rays in the 10 keV-1MeV energy band with excellent spatial and energy resolutions and without cryogenic cooling. In this contribution, we report on recent results of the CZT detector development program and several astrophysical experiments which make use of CZT detectors. In the first part of the paper, we discuss the performance of pixel and cross-strip CZT detectors read out with an ASIC developed at the Brookhaven National Laboratory. Our pixel detectors achieve some of the best energy resolutions reported in the literature. Cross-strip detectors are found to give an inferior performance and we investigate the reason for this performance difference. We also present results from a precision measurement of the effect of a steering grid on multi-pixel events obtained with a 200 micrometer collimator. In the second part of the paper, we describe the design and performance of the hard X-ray polarimeter X-Calibur. The polarimeter uses a 14 cm long scintillator scatterer, surrounded by an assembly of 32 2-5 mm thick CZT detectors. We discuss the sensitivity of the polarimeter to measure the linear polarization of 10 keV-80 keV X-rays on short and long balloon flights and results from testing the polarimeter in the laboratory.

The HEXAGONE balloon‐borne spectrometer has flown on 22 May 1989. HEXAGONE is a high resolution gamma‐ray spectrometer and consists of an array of twelve cooled germanium detectors. One of the observed targets was the Galactic Center and its vicinity (field of view 19° at 511 keV) and it was seen during 6.3 hours. The 511 keV annihilation line was observed with a flux of (8.88±2.67)×10−4 γcm−2 s−1, a width 1.09+1.38, −1.09 keV and its centroid at 511.54±0.38 keV. The results are consistent with an upper limit of 8.3×104 K for the temperature of the annihilation medium of the positrons.The HEXAGONE balloon‐borne spectrometer has flown on 22 May 1989. HEXAGONE is a high resolution gamma‐ray spectrometer and consists of an array of twelve cooled germanium detectors. One of the observed targets was the Galactic Center and its vicinity (field of view 19° at 511 keV) and it was seen during 6.3 hours. The 511 keV annihilation line was observed with a flux of (8.88±2.67)×10−4 γcm−2 s−1, a width 1.09+1.38, −1.09 keV and its centroid at 511.54±0.38 keV. The results are consistent with an upper limit of 8.3×104 K for the temperature of the annihilation medium of the positrons.

We report here on the optimization of 0.5 cm thick pixelated Orbotech CZT detectors with regards to the best contacting materials and the use of steering grids. We evaluated the performance of different contacting materials. Our study differs from earlier ones in that we investigated the performance of different anode and cathode materials separately. We obtain the best performance with Au cathodes. For different anode materials Ti and In give the best energy resolutions. The detector (2.0×2.0×0.5 cm3, 8×8 pixels) shows excellent 59 keV, 122 keV and 662 keV energy resolutions of 1.4 keV, 1.9 keV, and 7.4 keV, respectively. Furthermore, we report on using steering grids to improve on the performance of the pixelated detectors. Previously, the benefit of steering grids had been limited by additional electronic noise associated with currents between the negatively biased steering grids and the anode pixels. We are currently exploring the possibility to isolate the steering grid from the CZT substrates by a thin layer of Al2O3. We performed a series of measurements to determine by how much the isolation layer reduces the grid-pixel currents. Comparing the currents between two Au contacts before and after isolating one of the two contacts from the CZT with a 700 nm thick layer of Al2O3, we measure that the isolation layer reduces the currents by a factor of about 10 at 500 V. We present some results from a detector before and after deposition of an isolated steering grid. The grid indeed improves on the detectors energy resolution and detection efficiency. We show that simulations can be used to model the anode to cathode charge correlation in excellent agreement with the experimental results.

We explore the possibility to improve the performance of 0.5 cm thick cadmium zinc telluride (CZT) detectors with the help of steering grids on the anode side of the detectors. Steering grids can improve the energy resolution of CZT detectors by enhancing the small pixel effect; furthermore, they can increase their detection efficiency by steering electrons to the anode pixels which otherwise would drift to the area between pixels. Previously, the benefit of steering grids had been compromised by additional noise associated with currents between the steering grids and the anode pixels. We use thin film deposition techniques to isolate the steering grid from the CZT substrate by a 150 nm thick layer of the isolator Al2O3. While the thin layer does not affect the beneficial effect of the steering grid on the weighting potentials and the electric field inside the detector, it suppresses the currents between the steering grid and the anode pixels. In this contribution, we present first results from a 2times2times0.5 cm3 CZT detector with 8times8 pixels that we tested before and after deposition of an isolated steering grid. The steering grid improves the 662 keV energy resolution of the detector by a factor of 1.3 (from about 2% to about 1.5%), while not reducing the detection efficiency. To gain further insights into the detector response in the region between pixels, we measured energy spectra with a collimated 137Cs source. The collimator measurements can be used to enhance our understanding of energy spectra measured under flood illumination of the detectors

We describe the ``Monitor e Imageador de Raios-X'' (MIRAX), an X-ray astronomy satellite mission proposed by the high energy astrophysics group at the National Institute for Space Research (INPE) in Brazil to the Brazilian Space Agency. MIRAX is an international collaboration that includes, besides INPE, the University of California San Diego, the University of Tuebingen in Germany, the Massachusetts Institute of Technology and the Space Research Organization Netherlands. The payload of MIRAX will consist in two identical hard X-ray cameras (10 -200 keV) and one soft X-ray camera (2-28 keV), both with angular resolution of ~ 5-6 arcmin. The basic objective of MIRAX is to carry out continuous broadband imaging spectroscopy observations of a large source sample (~ 9 months/yr) in the central Galactic plane region. This will allow the detection, localization, possible identification, and spectral/temporal study of the entire history of transient phenomena to be carried out in one single mission. MIRAX will have sensitivities of ~ 5 mCrab/day in the 2-10 keV band (~2 times better than the All Sky Monitor on Rossi X-ray Timing Explorer) and 2.6 mCrab/day in the 10-100 keV band (~40 times better than the Earth Occultation technique of the Burst and Transient Source Experiment on the Compton Gamma-Ray Observatory). The MIRAX spacecraft will weigh about 200 kg and is expected to be launched in a low-altitude (~ 600 km) circular equatorial orbit around 2007/2008.

We report the first measurements of the 511 keV line emission from the Galactic Centre (GC) region performed with the spectrometer SPI on the space observatory INTEGRAL (International Gamma-Ray Astrophysics Laboratory). Taking into account the range of spatial distribution models which are consistent with the data, we derive a flux of 9.9(-2.1)(+4.7) x 10(-4) ph cm(-2) s(-1) and an intrinsic line width of 2.95(-0.51)(+0.45) keV (FWHM). The results are consistent with other high-spectroscopy measurements, though the width is found to be at the upper bound of previously reported values.

We describe the hard x-ray mission MIRAX - jointly proposed by teams from Brazil, the USA, Germany and the Netherlands. The scientific objective is to provide continuous 2-200 keV imaging of the central 1000 square degrees of our Galaxy for 9 months per year over up to 5 years. Durign times when the sun crosses the Galactic Center other areas like the Cygnus-, Vela- and the Magellanic Cloud-regions can be observed. MIRAX will detect, localize, identify and study sources of medium to hard x-ray emission, with special emphasis on short-lived, rare and unpredictable events, including weak x-ray transients and fast x-ray movae. MIRAX will reach in a one day observation a sensitivity of 1mCrab in 2-10 keV and 2.5mCrab in 10-100keV. MIRAX will provide a unique capability to study compact galactic objects - notably accreting neutron stars and black holes. It will:- Probe neutron star and x-ray burst theory wiht 20,000 type I x-ray bursts and 50 'superbursts' - Measure spin frequencies of neutron stars from 10-100 burst oscillations - Observe explosive flares and x-ray light curves during ejections in superluminal jets - Study soft gamma-ray repeaters, fast x-ray novae and new types of phenomena yet to be discovered. We describe the science and the instrumentation.

The SPI instrument has been launched on-board the INTEGRAL observatory on October 17, 2002. SPI is a spectrometer devoted to the sky observation in the 20 keV-8 MeV energy range using 19 germanium detectors. The performance of the cryogenic system is nominal and allows to cool the 19 kg of germanium down to 85 K with a comfortable margin. The energy resolution of the whole camera is 2.5 keV at 1.1 MeV. This resolution degrades with time due to particle irradiation in space. We show that the annealing process allows the recovery of the initial performance. The anticoincidence shield works as expected, with a low threshold at 75 keV, reducing the GeD background by a factor of 20. The digital front-end electronics system allows the perfect alignement in time of all the signals as well as the optimisation of the dead time (12%). We demonstrate that SPI is able to map regions as complex as the galactic plane. The obtained spectrum of the Crab nebula validates the present version of our response matrix. The 3sigma sensitivity of the instrument at 1 MeV is 8x10(-7) ph cm(-2) s(-1) keV(-1) for the continuum and 3x10(-5) ph cm(-2) s(-1) for narrow lines.

The SPI instrument has been launched on-board the INTEGRAL observatory on October 17, 2002. SPI is a spectrometer devoted to the sky observation in the 20 keV-8 MeV energy range using 19 germanium detectors. The performance of the cryogenic system is nominal and allows to cool the 19 kg of germanium down to 85 K with a comfortable margin. The energy resolution of the whole camera is 2.5 keV at 1.1 MeV. This resolution degrades with time due to particle irradiation in space. We show that the annealing process allows the recovery of the initial performance. The anticoincidence shield works as expected, with a low threshold at 75 keV, reducing the GeD background by a factor of 20. The digital front-end electronics system allows the perfect alignement in time of all the signals as well as the optimisation of the dead time (12%). We demonstrate that SPI is able to map regions as complex as the galactic plane. The obtained spectrum of the Crab nebula validates the present version of our response matrix. The 3 σ sensitivity of the instrument at 1 MeV is 8 10ph·cm·s·keV for the continuum and 3 10ph·cm·s for narrow lines.

We present the analysis of the first observations of the Cygnus region by the SPI spectrometer onboard the Integral Gamma Ray Observatory, encompassing similar to600 ks of data. Three sources namely Cyg X-1, Cyg X-3 and EXO 2030+375 were clearly detected. Our data illustrate the temporal variability of Cyg X-1 in the energy range from 20 keV to 300 keV. The spectral analysis shows a remarkable stability of the Cyg X-1 spectra when averaged over one day timescale. The other goal of these observations is SPI inflight calibration and performance verification. The latest objective has been achieved as demonstrated by the results presented in this paper.

SPI is a high spectral resolution gamma-ray telescope on board the ESA mission INTEGRAL (International Gamma Ray Astrophysics Laboratory). It consists of an array of 19 closely packed germanium detectors surrounded by an active anticoincidence shield of BGO. The imaging capabilities of the instrument are obtained with a tungsten coded aperture mask located 1.7 m from the Ge array. The fully coded field-of-view is 16degrees, the partially coded field of view amounts to 31degrees, and the angular resolution is 2.5degrees. The energy range extends from 20 keV to 8 MeV with a typical energy resolution of 2.5 keV at 1.3 MeV. Here we present the general concept of the instrument followed by a brief description of each of the main subsystems. INTEGRAL was successfully launched in October 2002 and SPI is functioning extremely well.

Well detectors are pixelized gas proportional counters that are true two-dimensional imagers. Well detectors are attractive not only for their imaging capabilities (currently less than 300 mm FWHM resolution), but they are also economical to produce and simple to operate even in very large areas. These detectors are mechanically robust, highly stable even at large gas gains and operate at room temperature. We are developing well detectors for large-area (~400 cm2) X-ray imagers, as well as for very large-area (>10 m2) electron trackers for gamma-ray imaging. We describe the fabrication and performance of our 5 x 5 cm2 prototypes and discuss our development plans for both X-ray imagers and electron trackers. This includes demonstrating the technology for focal plane detectors for LOBSTER-ISS, a capillary-optic soft X-ray monitor proposed for the International Space Station in 2006.

We are designing the Minute of Arc Resolution Gamma-ray Imaging Experiment (MARGIE) as a 100 day Ultra Long Duration Balloon (ULDB) mission to: a) detect and localize gamma-ray bursts; and b) survey the hard X-ray sky. Major advances in designing the CZT detectors increase the senstitivity to higher energy. Design of the gondola has also progressed.

The FAR-XITE is a proposed Balloon Payload that consists of 10 nested mirror modules. The mirrors are coated with multilayers that allow FAR_XITE to reach 100 keV with better than 1 arcminute angular resolution. We describe the science objectives, optical design and specifications, and present our recent results of advances in X-ray mirror fabrication techniques.

The INTErnational Gamma Ray Astrophysics Laboratory (INTEGRAL) mission's onboard spectrometer, the INTEGRAL spectrometer (SPI), is described. The SPI constitutes one of the four main mission instruments. It is optimized for detailed measurements of gamma ray lines and for the mapping of diffuse sources. It combines a coded aperture mask with an array of large volume, high purity germanium detectors. The detectors make precise measurements of the gamma ray energies over the 20 keV to 8 MeV range. The instrument's characteristics are described and the Monte Carlo simulation of its performance is outlined. It will be possible to study gamma ray emission from compact objects or line profiles with a high energy resolution and a high angular resolution.

The HEXIS (High Energy X-Ray Imaging Spectrometer) is a MIDEX-class mission concept to perform a deep survey and continuous monitoring of nearly the entire sky in the 5-200 keV band. It uses arrays of position-sensitive Cadmium-Zinc Telluride (CZT) detectors and coded masks to achieve 26/ resolution and a 5 sigma sensitivity (> 20 keV) of 4 milliCrab in one day and 0.2 milliCrab in one year. With these capabilities it is estimated that similar to 5000 sources can be discovered and localized and have their spectra and variability characterized. Hundreds of gamma-ray bursts would be detected each year and localized to < 20/. HEXIS also contains a narrow field, 5 degrees, coded mask imager for detailed studies of selected regions. This has three are minute resolution and is seven times more sensitive than the all-sky system. The HEXIS detector concept uses crossed strip readout to achieve 0.5 mm resolution pixels for large area arrays, similar to 400 cm(2). This technique is under development at UCSD and Washington University. Detectors have been studied with tuneable monochromatic x-ray beams and mapped with finely collimated 30 micron beams. These results show that the crossed strip readout has the necessary spatial and spectral characteristics. The HEXIS concept is described and results are presented on the detectors' spatial and spectral properties.

The absence of a BATSE line detection during the mission’s first six years has led to a statistical analysis of the occurrence of lines in the BATSE database; this statistical analysis will still be relevant if lines are detected. We review our methodology, and present new simulations of line detectability as a function of the line parameters. We also discuss the calculation of the number of “trials” in the BATSE database, which is necessary for our line detection criteria.

The International Gamma-ray Astrophysics Laboratory (INTEGRAL) is conceived as the next logical step in gamma-ray astronomy after the US Compton Gamma-Ray Observatory (CGRO) and the French/Russian SIGMA mission.The INTEGRAL scientific payload consists of two main instruments (Imager and Spectrometer) and two monitor instruments (X-Ray Monitor and Optical Transient Camera).The INTEGRAL spectrometer "SPI" is optimized for detailed measurements of gamma-ray lines and mapping of diffuse sources. It combines a coded aperture mask with an array of large volume, high-purity germanium detectors. The detectors make precise measurements of the gamma-ray energies over the 20 keV-8 MeV energy range.This paper presents the instrument characteristics these properties have been evaluated by means of Monte Carlo calculations. With the characteristic features It will be possible to study gamma-ray emission from compact objects or line profiles with a high-energy resolution and a good angular resolution.

SPI (Spectrometer for INTEGRAL) is a high spectral resolution gamma-ray telescope using cooled germanium detectors that will, be flown on board the INTEGRAL mission in 2001. It consists of an array of 19 closely-packed germanium detectors surrounded by an active bismuth germanate (BGO) anti-coincidence shield. The instrument operates over the energy range 20 keV to 8 MeV with an energy resolution of 1-5 keV. A tungsten coded-aperture mask located 1.7 m from the detector array provides imaging over a 15 degrees fully-coded field-of-view with an angular resolution of similar to 3 degrees. The point source narrow-line sensitivity is estimated to be 3-7 x 10(-6) ph cm(-2) s(-1) over most of the range of the instrument (E > 200 keV) for a 10(6) s observation. With its combination of high sensitivity, high spectral resolution and imaging, SPI will improve significantly over the performance of previous instruments such as HEAO-3, OSSE, and Comptel. It can be expected to take a major step forward in experimental studies in nuclear astrophysics. The SPI instrument is being developed under the auspices of the European Space Agency by a large international team of scientists and engineers in both Europe and the United States.