The fourth Japanese x-ray astronomy satellite, ASCA, carries two imaging gas scintillation proportional counters (GIS) on its focal plane. Extensive ground calibration has established its position resolution to be 0.5 mm and FWHM energy resolution to be 8.0% both at 6 keV. When combined with the x-ray telescope, a sensitivity range becomes 0.7 - 10 keV. These properties have been confirmed through in-orbit calibrations. The in-orbit background of the GIS has been confirmed to be as low as (5 - 7) X 10^-4 c s^-1cm^-2keV^-1 over the 1 - 10 keV range. The long-term detector gain is stable within a few % for two years. Gain dependence on the position and temperature has been calibrated down to 1%. The overall energy response is calibrated very accurately. Thus the GIS is working as an all-round cosmic x-ray detector.

CHIP -- the continuous hard x-ray imager for astrophysics) -- is a powerful hard x ray imaging spectroscopy mission, an order of magnitude more sensitive to hard x rays than XTE, comprised of the large uniform coverage imager (LUCY) for all-sky coverage and the deep extragalactic survey imager (DESI) for more sensitive pointed observations. Both instrument complements will utilize the room temperature semiconductor CdZnTe in mosaiced arrays of position sensitive devices in conjunction with coded masks. Each unit will provide imaging from 2 - 100 keV with approximately 1 keV energy resolution throughout the entire energy range and few arcminute intrinsic spatial resolution. LUCY will provide (1) a complete flux- limited sample of the hard x-ray contents of our galaxy as well as of the extragalactic sky, (2) alarms and precise positions for transient phenomena on all timescales from seconds to days, and (3) continuous spectral/temporal studies of these objects over a vast range of timescales from seconds to days, to months, to years. DESI will extend LUCY's coverage even deeper by viewing a small portion of the hard x-ray sky (0.01 sr) for background limited studies of individual objects considerably deeper than present or future hard x-ray instruments.

The Marshall Space Flight Center, Alabama in a teaming arrangement with the Naval Research Laboratory, Maryland has developed the ISIS (impulsive solar imaging spectrometer) mission for viewing the sun and the sky in the EUV, soft, and hard x rays. The soft and hard x ray imaging as well as the gamma-ray spectroscopy will be provided by a three axis pointed Fourier telescope (i.e. a spatial modulation collimator). The EUV imager will be a supporting context instrument. This paper describes the optimized instrument concept and discusses the associated trades made in developing it. For example, the numbers of spatial frequencies measured versus the sensitivity needed for imaging weak sources is discussed in detail. ISIS builds upon the YOHKOH findings in that the telescope is tailored to image compact simple loop sources. Only two spatial frequencies need be measured, allowing substantial gains in sensitivity. In addition, this allows both the real and imaginary Fourier components to be measured, which is a vast improvement over approaches that measure only the real components.

We describe the design concept for the highly integrated Pluto payload system (HIPPS): a highly integrated, low-cost, light-weight, low-power instrument payload designed to fly aboard the proposed NASA Pluto flyby spacecraft destined for the Pluto/Charon system. The HIPPS payload is designed to accomplish all of the Pluto flyby prime (IA) science objectives, except radio science, set forth by NASA's Outer Planets Science Working Group (OPSWG) and the Pluto Express Science Definition Team (SDT). HIPPS contains a complement of three instrument components within one common infrastructure; these are: (1) a visible/near UV CCD imaging camera; (2) an infrared spectrograph; and (3) an ultraviolet spectrograph. A detailed description of each instrument is presented along with how they will meet the IA science requirements.

We present a space mission concept for a low energy gamma-ray telescope, ATHENA, which is under investigation as the next major advance in gamma-ray spectroscopy following the current COMPTON Gamma Ray Observatory and the planned INTEGRAL missions. The instrument covers the nuclear line emission energy domain with dramatically improved sensitivity and spectral resolution. The baseline configuration combines a high resolution Compton telescope constructed from Ge planar strip detectors for the 0.3 - 10 MeV energy region with a coded-aperture system for the 10 - 200 keV domain. The Ge Compton telescope provides a broad field of view with exceptional spectral and imaging resolution. The requirements, capabilities and simulations of ATHENA are discussed.

The ASTRO-E satellite is scheduled for launch in 2000 by the Institute of Space and Astronautical Science (ISAS). In this paper the design and performance of the hard x ray detector (HXD) developed for ASTRO-E are described. The HXD is a combination of YAP/BGO phoswich scintillators and silicon PIN diodes covering a wide energy band of 10 - 700 keV. The detector background is reduced down to several times 10^-6c/s/cm²/keV, and the sensitivity of the HXD is more than one order of magnitude higher than any other past missions in the range of a few 10 keV to several 100 keV. Thus ASTRO-E HXD is expected to achieve an extreme high performance for detecting cosmic hard x rays and low-energy gamma rays. Astrophysics to be explored with the HXT are expected to be extremely widespread and rich.

The Advanced X-ray Astrophysics Facility (AXAF) is a major NASA space observatory and is scheduled for launch in 1998. AXAF will perform high spatial and spectral resolution observations of celestial sources in the soft x-ray band 0.1 - 10 keV. The high resolution camera (HRC) is one of two focal plane instruments being developed for the AXAF. The HRC will be capable of observing point and extended sources with high sensitivity and high spatial resolution and will be used to record the high resolution spectra produced by an objective transmission grating. The HRC is based on microchannel plates (MCPs). We describe the design and development of the HRC, its expected performance, and some of its observational goals. The HRC consists of two separate detectors, HRC-I (imaging) and HRC-S (spectroscopy). HRC-I is used for imaging and has a field of view of 31 arc min by 31 arc min and a spatial resolution of less than 25 micrometers (equivalent to less than 0.5 arc sec). HRC- S is optimized to readout the spectrum of AXAF's low energy transmission grating (LETG) and this combination will achieve resolving powers in excess of 1000 at low energies and cover a wavelength range of 4 to 140 angstroms.

The Advanced X ray Astrophysics Facility (AXAF) contains two focal-plane science instruments -- the microchannel-plate high-resolution camera (HRC) and the AXAF CCD imaging spectrometer (ACIS). Each of these instruments provides two low-internal- background detectors, one for imaging and the other for reading out AXAF's objective transmission gratings. Taking maximum advantage of the low internal background of these instruments requires shielding against external electromagnetic and particle radiation. To optimize the shielding within weight constraints, we performed extensive numerical simulations of the photon transport and of the particle transport and activation within the AXAF. We discuss the simulations and report the results of the shielding study. With the adopted shielding design, the particle-induced background and the x-ray-induced background are each comparable to or less than the anticipated internal background of AXAF's imaging detectors (HRC and ACIS). Thus, the predicted total non-imaged background is very low -- less than 0.2 counts arcsec^-2 day^-1 for the HRC and even lower for the ACIS half-arcsec angular resolution, this low background has negligible effect upon point-source detection, for reasonable observation durations.

The prime focal instrument of the x-ray astronomy satellite ROSAT is the position sensitive proportional counter (PSPC). It is a conventional multiwire gas counter for the energy range from 0.1 to 2.4 keV. At a photon energy of 1 keV the PSPC has an energy resolution of 41% (FWHM), a position resolution of 230 micrometer and a quantum efficiency of 50%. With its very high charged particle background rejection efficiency of better than 99% the detector is best suited for deep exposures to reach so far unprecedented low x-ray flux limits, and also for imaging of extended low surface brightness objects. We describe the detector, report on its in- orbit performance, and present some highlights of the ROSAT all-sky survey and from pointed PSPC observations.

We are developing a field-widened spatial heterodyne spectrometer (SHS) for suborbital observations of the hot component of the diffuse interstellar medium. Our goal for these observations is to obtain the first velocity-resolved (20 km/s) line profiles of the C IV 154.8, 5.1 nm emission line from the Cygnus loop and from one direction at high galactic latitude. Long term, our interest is to develop an SHS instrument for a radial-velocity-resolved sky survey of the 10⁵ K 'coronal gas' in the interstellar medium using a small satellite. This paper reviews the scientific motivation and SHS concept and then discusses in more detail the optical design of the sounding rocket payload and the data taking strategy for the observations.

The cosmic unresolved background instrument using CCDs (CUBIC) is currently scheduled for launch on the Argentine/US SAC-B satellite late this year. This instrument is designed to perform moderate resolution nondispersive x-ray spectroscopy of the diffuse x-ray background over the band 0.2 - 10.0 keV using state-of-the-art photon-counting CCDs. The instrument is optimized for spectroscopy of diffuse emission with a field of view of 5 degrees by 5 degrees below 1 keV and 10 degrees by 10 degrees above 3 keV. Observations will typically last 1 - 3 days, and will obtain high quality CCD spectra of the diffuse background, nearby superbubbles and supernova remnants, and the brightest x-ray point sources. This paper gives an overview of the instrument design and CCD detectors.

CUBIC, the cosmic unresolved x ray background instrument using CCDs, is instrumented to make moderate resolution x-ray spectral measurements of diffuse targets at spatial scales of a few degrees. While the energy range is nominally 200 eV - 10 keV, the CCDs have been designed to maximize the soft x ray performance by using novel structures. A two part aperture increases the area-solid angle product above 1 keV to maximize sensitivity to the cosmic component of the diffuse x ray background. Here we report preliminary results of our preflight laboratory calibrations performed at Penn State of the dark current, readnoise, nonlinearity, charge transfer efficiency, energy resolution, and quantum efficiency of the two flight CCDs. We also discuss calibration of the detector field of view and the preliminary area-solid angle product of the instrument.

We present the results of a comparison of data processing algorithms to be used with space- borne x-ray CCD cameras such as those aboard ASCA, CUBIC and AXAF. The goal is to optimize efficiency and accuracy based upon the capabilities and limitations of the on-board processors. We examine the two main components of processing: determination of the bias (or zero) -level, and event recognition. An algorithm to generate a pixel-by-pixel bias by on-board processing is developed and tested. The on-board bias frame is compared to a bias created from a standard laboratory pixel-by-pixel averaging of dark frames. We show that an accurate pixel-by-pixel bias frame can be created with an on-board algorithm in as few as 15 frames. We show that a bias frame created from that algorithm performs as well as meanframes created in the laboratory. On-board algorithms that handle bias determination and event selection simultaneously are also developed. We show that several types of these algorithms successfully process the CCD data, although the algorithm should be chosen according to the specific capabilities of the processors. The procedures were evaluated by examining event quality and single/split event ratios, and more importantly by the determination of spectral energy resolution (e.g., the FWHM of ⁵⁵Fe). The algorithms were compared and evaluated for laboratory data from several different cameras and types of CCD devices.

We have proposed a gamma-ray burst mission concept called burst arcsecond imaging and spectroscopy (BASIS) in response to NASA's announcement for new mission concept studies. The scientific objectives are to accurately locate bursts, determine their distance scale, and measure the physical characteristics of the emission region. Arcsecond burst positions (angular resolution approximately 30 arcsec, source positions approximately 3 arcsec for greater than 10^-6 erg cm^-2 bursts) are obtained for about 100 bursts per year using the 10 - 200 keV emission. This allows the first deep, unconfused counterpart searches at other wavelengths. The key technological breakthrough that makes such measurements possible is the development of CdZnTe room-temperature semiconductor detectors with fine (approximately 100 micron) spatial resolution. Fine spectroscopy is obtained between 0.2 keV and 200 keV. The 0.2 keV threshold allows the first measurements of absorption in our galaxy and possible host galaxies, constraining the distance scale and host environment. The mission concept and its scientific objectives are described.

We have begun to study a mission to carry out the first high sensitivity imaging survey of the entire sky at hard x-ray energies (5 - 600 keV). The Energetic X-ray Imaging Survey Telescope (EXIST) would include 2 - 4 large area coded aperture telescopes with offset fields of view allowing total exposures of >= 500 ksec and flux sensitivities below 1 mCrab over the full sky in a year with time resolution from msec to months for each source as well as high spatial and spectral resolution for sources, transients and gamma-ray bursts. A pointed observatory phase, with the telescopes co-aligned, would follow and achieve still greater sensitivities and temporal coverage, allowing the detailed study of virtually all classes of accretion sources (cataclysmic variables to quasars) as well as diffuse galactic emission. The baseline concept originally proposed for the detector is a modularized array (4 X 4) of Cd-Zn-Te crystals (6.25 cm² each, or 100 cm²/module). An array of 5 X 5 modules, or 2500 cm² total detector area with 1.25 mm spatial resolution, would constitute the focal plane readout of each of the four telescopes. A brief descriptio of the proposed detector and telescopes and predicted backgrounds and sensitivity is given.

We report on the status of modifications to an existing extreme ultraviolet (EUV) telescope/spectrograph sounding rocket payload for planetary observations in the 800 - 1200 angstrom wavelength band. The instrument is composed of an existing Wolter Type II grazing incidence telescope, a newly built 0.4-m normal incidence Rowland Circle spectrograph, and an open-structure resistive-anode microchannel plate detector. The modified payload has successfully completed three NASA sounding rocket flights within 1994 - 1995. Future flights are anticipated for additional studies of planetary and cometary atmospheres and intersteller absorption. A detailed description of the payload, along with the performance characteristics of the integrated instrument are presented. In addition, some preliminary flight results from the above three missions are also presented.

Germanium strip detectors combine high quality spectral resolution with two-dimensional positioning of gamma-ray interactions. Readout is accomplished using crossed electrodes on opposite faces of a planar germanium detector. Potential astrophysics applications include focal plane detectors for coded-aperture or grazing incidence x-ray mirror imagers, and as detection elements of a high resolution Compton telescope. We report on test results of two germanium strips detectors, one with 2 mm position resolution, the other with 9 mm. We discuss general device performance in terms of energy and position resolution, crosstalk effects, potential applications, and a demonstration of imaging properties.

Superconducting tunnel junctions can be used as high resolution x-ray and gamma-ray detectors. Until recently, most results were from detectors that consisted of niobium and aluminum thin films deposited on insulating substrates. Typically Nb films with thicknesses of several hundred nanometers are used as absorbers. These thin film devices inherently suffer from poor quantum efficiency. To increase this efficiency a foil or a single crystal, which can be thicker and can have a larger area than the thin films, can be used as the superconducting absorber. We are working on using ultra-pure, high-Z, superconducting crystals as the x-ray and gamma-ray absorbers. We are planning to fabricate a detector which uses a 10 micrometer-thick Ta crystal as the absorber, which will have a quantum efficiency of greater than 99% at 6 keV. As a test of the different processing steps we fabricated Al/AlOx/Al superconducting tunnel junctions on top of a 30 micrometer thick Al foil. In this paper several of the fabrication issues involved are presented as well as the first results from the Al foil test devices.

Superconducting tunnel junctions can be used as part of a high-resolution, energy-dispersive x- ray detector. The energy of the absorbed x ray is used to break superconducting electron pairs, producing on the order of 10⁶ excitations, called quasiparticles. The number of quasiparticles produced is proportional to the energy of the absorbed x ray. When a bias voltage is maintained across the barrier, these quasiparticles produce a net tunneling current. Either the peak tunneling current or the total tunneled charge may be measured to determine the energy of the absorbed x ray. The tunneling rate, and therefore the signal, is enhanced by the use of a quasiparticle trap near the tunnel barrier. The trapping efficiency is improved by decreasing the energy gap, though this reduces the maximum temperature at which the device may operate. In our niobium/aluminum configuration, we can very the energy gap in the trapping layer by varying its thickness. This paper examines the performance of two devices with 50 nm aluminum traps at temperatures ranging from 100 mK to 700 mK. We found that this device has a very good energy resolution of about 12 eV FWHM at 1 keV. This energy resolution is independent of temperature for much of this temperature range.

Measurements are presented on the x ray response of superconducting tunnel junction (STJ) detectors, over the energy range of 50 - 1800 eV. This includes the measurement of the lowest x-ray energies published to date. Energy resolution and response linearity is measured as a function of device geometry. It is shown that self-recombination of quasi-particles leads to an energy non-linearity which depends on junction volume. The effect of count rate limitations on energy resolution is established for rates up to 10 kHz.

The possibility of using superconducting tunnelling junctions (STJ) coupled to a crystal absorber for x-ray spectroscopy has been investigated in the range 1 to 22 keV. Photo- electrons created as a result of the x-ray photo-absorption in a suitable crystal will give rise to phonon production in the crystal-absorber. A matrix of STJs mounted on this absorber can be used essentially as microphones to detect these phonons. The total energy detected by the matrix provides a measure of the absorbed photon's energy while the distribution through the matrix provides the spatial resolution. The use of a suitable crystal absorber should significantly improve the efficiency at higher energies. This is a serious limitation which faces STJs, when used to directly absorb the radiation above a few keV.

Measurements of the x ray response of niobium-based superconducting tunnel junctions with Al trapping layers are presented. Signal amplitudes equivalent to as many as 2.3 multiplied by 10⁸ tunneled electrons for a 5.9 keV photon are observed, corresponding to an amplification factor of approximately 100 per initially created quasiparticle in niobium. The detectors, however, exhibit a significant non-linearity in their energy response. The energy resolution is approximately 140 eV FWHM at 5.9 keV.

The ROSAT (Roentgen Satellite) observatory was launched 1990 June 1, with a microchannel- plate-based high resolution imager (HRI) as one of the focal plane instruments of its primary soft x-ray telescope. Exhaustion of the gas supply for ROSAT's other focal-plane detector has left the HRI as the sole instrument for continuing the program of celestial soft x ray observations. The long-term behavior of the HRI is presented, with descriptions of imaging performance, quantum efficiency and gain stability, spectral resolution, UV response, and background characteristics.

We report on the results of a synchrotron calibration of two identical microchannel plate (MCP) detectors carried out at the CCL Daresbury synchrotron radiation source (SRS). The SRS was run with low ring current to allow operation of the detectors in photon-counting mode. Both detectors were half coated with KBr and half with CsI. Detector 1 was calibrated, for both photocathodes, in 1 eV steps over the energy range 50 - 350 eV, on SRS beamline 6.1. We present measurements of edge-related absolute quantum efficiency features arising from both the photocathodes and the underlying lead silicate glass. We also describe the results of charge abstraction lifetests of Detector 1, made possible by the small cross section and relatively high peak count rate of the line 6.1 x-ray beam. A preliminary analysis of the calibration of detector 2 in 3 eV steps over the energy range 2000 - 6000 eV (on IRC beamline 4.2) is also presented.

We have previously demonstrated the enhanced performance of progressive geometry readouts, such as the SPAN two dimensional charge division readout, in MCP based detectors. The nine electrode two-dimensional Vernier readout described in this paper is the latest development in this series of devices. The Vernier readout uses three triplets of electrodes, each triplet consisting of three electrodes whose areas vary sinusoidally and whose phases are each displaced by 120 degrees. The co-ordinate of an event at any point in the active area of the readout is encoded uniquely by the three phases, one phase being generated by each triplet. The Vernier technique uses only the phase information encoded by the electrode areas, whereas previous designs, such as SPAN, also relied on modulation of the sinusoidal amplitude to encode a co-ordinate uniquely. The sensitivity to varying charge footprint size caused by this reliance is thus avoided in the Vernier readout. In addition, fixed pattern noise in the image, resulting from signal digitization prior to phase calculation, is avoided by encoding the final x and y co-ordinates as linear combinations of all three phases. The pattern geometry can be chosen to ensure that the fixed pattern noise in each phase never coincides with that in other phases when combined in the decoding algorithm. We present images and performance data from an MCP based detector using a one Vernier anode, with an active diameter of 25 mm. A first image from the nine electrode two dimensional Vernier anode is shown and its preliminary performance is discussed.

The microchannel plates for the detectors in the SUMER and UVCS instruments aboard the Solar Orbiting Heliospheric Observatory (SOHO) mission to be launched in late 1995 are described. A low resistance Z stack of microchannel plates (MCPs) is employed in a detector format of 27 mm multiplied by 10 mm using a multilayer cross delay line anode (XDL) with 1024 by 360 digitized pixels. The MCP stacks provide gains of greater than 2 multiplied by 10⁷ with good pulse height distributions (as low as 25% FWHM) under uniform flood illumination. Background rates of approximately equals 0.6 event cm^-2 sec^-1 are obtained for this configuration. Local counting rates up to approximately equals 800 events/pixel/sec have been achieved with little drop of the MCP gain. MCP preconditioning results are discussed, showing that some MCP stacks fail to have gain decreases when subjected to a high flux UV scrub. Also, although the bare MCP quantum efficiencies are close to those expected (approximately equals 10%), we found that the long wavelength response of KBr photocathodes could be substantially enhanced by the MCP scrubbing process. Flat field images are characterized by a low level of MCP fixed pattern noise and are stable. Preliminary calibration results for the instruments are shown.

The high resolution camera (HRC) will be one of the two focal plane instruments on the Advanced X-ray Astrophysics Facility (AXAF). AXAF is a major NASA space observatory and is scheduled for launch in 1998. The essential elements of the HRC instruments are chevron pairs of microchannel plates (MCPs). The HRC MCPs provide x ray conversion and electron multiplication while maintaining high spatial and temporal resolution. In addition, the HRC MCPs will be the largest format, the lowest internal background, and the highest resolution of any MCP-based x-ray imaging detector. This paper presents results obtained in testing and evaluating flight candidate MCPs with emphasis on their low internal background out-of-band (high energy) response and their spatial uniformity.

The microsphere plate (MSP) is a new type of electron multiplier device operating along similar lines to the well known microchannel plate (MCP). The MSP is manufactured by El- Mul Technologies Ltd., using glass beads 20 to 60 micrometer diameter, sintered together to form a wafer less than 1 mm thick. Conductive coatings are applied to the upper and lower surfaces, and a high voltage is applied between these two electrodes, allowing secondary electron multiplication to take place. The device uses the surfaces of the randomly arranged interstices of the sintered glass beads as dynodes, whereas in the MCP, dynodes are constituted by the inner surfaces of the longitudinal pores. The homogeneous composition of the MSP causes charge to spread laterally during multiplication, resulting in a spatial resolution of about 2 linepairs/mm when proximity focused to a phosphor. Charge division readouts benefit from this charge spreading, such as the wedge and strip anode which requires a charge footprint of order 1 - 2 mm diameter. We present results of experiments on the imaging performance of detectors using MSPs with readouts such as the wedge and strip anode. We discuss and quantify the potential advantages to be gained from MSPs, such as the higher gain achievable per stage, reduced susceptibility to paralysis owing to their isotropic conductivity, etc. Potential MSP disadvantages, such as image nonlinearities, quantum efficiency variability, and pulse height saturation are analyzed.

Microsphere plates (MSPs), a new type of electron multiplier, consisting of sintered disks of glass beads, have recently become available from El-Mul Technologies Ltd. The principles of MSP operation are similar to those of microchannel plates (MCPs). This paper reports a survey of the gain, resistance, dark noise, count rate capability, charge abstraction lifetime, and image characteristics of a number of standard 33 mm diameter microsphere plates (of thickness 0.7 and 1.4 mm), operated both singly and as two-stage multipliers. We also describe a simple Monte-Carlo model of MSP operation, which enables us to estimate numerically a number of MSP characteristics, including (1) output pulse height distributions (PHDs), (2) output electron spatial and energy distributions, and (3) transit time distributions.

A photon-counting intensified charge injection device (CID) detector is currently in development at the Laboratory for Astronomy and Solar Physics at the Goddard Space Flight Center. Analogous microchannel-plate-intensified CCD detectors have achieved impressive spatial resolution performance in photon-counting operation. Such detectors suffer, however, from a severe limitation on local dynamic range; local event rates must be kept low in order to minimize event overlap at the frame rates achievable for reading out a full CCD. By utilizing a random access CID for the readout stage, we plan to avoid this severe local count rate limitation by virtue of the addressable (rather than serial) readout capability of such a device. Different portions of the detector field can be framed at different rates, as appropriate to the brightness distribution of the scene, maximizing the local count rate limit for a given pixel read rate and event processing capability. A high spatial resolution, high count rate photon counting detector of this type is of interest in a number of applications in space and ground- based astronomy. In this report, we present: (1) the advantages and applications of this kind of detector, (2) remarks on the suitability of different CID architectures, (3) our system design concept, and (4) the status and plans for our fabrication and testing efforts.

We present a progress report on the development of intensified charge coupled devices (ICCDs) used in both analog mode with CCD integrating the output of an MCP and in photon counting mode where single MCP events are centroided to subpixel accuracy by the CCD and readout electronics. Spatial resolutions of 36 lp/mm have been achieved using a 15 micrometer pitch MCP in the analog mode. In the photon counting mode, individual MCP pores with the same spacing have been easily resolved indicating spatial resolutions of less than 10 micrometer. A discussion of the centroiding algorithms are presented, as well as a description of the electronic designs that will increase the diffuse event rate of the photon counting ICCD to 50,000 events/sec.

We describe a new position readout scheme, applicable to proportional counters, which provides the attributes required for large format, high energy x-ray detectors, such as that proposed for the Eixon x-ray monitor instrument on the ESA INTEGRAL mission. Large format detectors for coded mask imaging require a position resolution of typically less than 1 mm, in order to over-sample the projected mask pixel. Background rejection at higher energies can be improved by using fluorescence gating. However, this technique requires the position readout to be capable of detecting the simultaneous double event signature. The scheme we propose combines both excellent position resolution with the ability to resolve simultaneous events. The readout scheme consists of an array of charge measurement electronic channels connected to groups of cathode strips. The particular cathode grouping arrangement allows a large reduction (approximately 1/6) in the number of channels required compared to the fully parallel scheme, with one channel per electrode. However, the new design still retains the charge centroiding and parallel processing capabilities of the fully parallel scheme, enabling it to provide high spatial resolution and resolve multiple simultaneous events. We present results of a Monte Carlo simulation of the detector and readout. The simulation models the physics involved in each x ray interaction and predicts the primary ionization distribution. Simulation of electron diffusion and gas multiplication are used to predict the charge induced on each cathode strip. Electronic noise and other signal degradation factors are included for a realistic assessment of readout performance. Thus far, the position readout is modeled in one axis only. The success of the new scheme is assessed by comparison with the fully parallel readout.

Based on experimental data obtained with a xenon filled low energy gas scintillation proportional counter (LE-GSPC) the performance and characteristics of such detectors are discussed in the context of their spectroscopic capabilities. Measurements were made at a synchrotron radiation facility, taking advantage of the tuneability and excellent collimation of the source. The energy linearity and the associated discontinuities at the xenon absorption edges are described for the range 0.15 to 6 keV. The results relating to the energy resolution as a function of energy and the L-escape peaks are also presented.

The potential performance characteristics of a liquid Xe proportional counter are discussed. Benefits in terms of spatial resolution, energy range, operating voltage, and energy resolution are possible. Practical problems, such as readout, purity, microstrip charging, and charge recombination, are reviewed. A preliminary observation of a gain of approximately 10 using a microstrip detector in liquid Xe is reported.

It was discovered in accelerator experiments that after intense pulse irradiation the energy resolution of LXe gamma-spectrometer is temporally worsened and then is restored. Both the threshold of distortion and time of recovery depend on detector sizes and strength of electric field. The reason for such phenomenon is accumulation of positive ions. Analysis of sources of pulse irradiation in cosmic experiments shows that doses in these pulses can be more then threshold but because of too low a frequency of the pulsed events the worsening of energy resolution is not important for measurements during long intervals of time. However, in the spectra measurement of pulsed events considerations of this paper can be essential.

The high energy transmission grating spectrometer (HETGS) for the Advanced X-ray Astrophysics Facility (AXAF) uses transmission gratings of period 2000 and 4000 angstrom to diffract x rays in the energy range 400 - 9000 eV. The gratings are so-called phased gratings, where the phase shift of x rays through the grating bars causes constructive interference at some wavelengths, thereby increasing the efficiency (in first order) to a level higher than would be expected for an opaque grating. AXAF has a program goal of calibrating the efficiencies (or effective areas) of the various spectrometers and imaging detectors (including the contribution of the x-ray mirrors) to an accuracy of a few percent. The HETGS group has elected to attempt a calibration at the sub-assembly level (i.e., the grating elements only, independent of the detectors and mirrors) at the 1% level. Since it is impossible (in practice) to measure grating efficiencies for all of the AXAF grating elements (336 elements in the flight assembly) at all energies, we have chosen instead to develop a model of the diffraction efficiency in all orders, and determine the parameters of the model by measuring the diffraction efficiencies at a few x ray energies. We verify the model by detailed studies of a few gratings made at the National Synchrotron Light Source. To date, we believe that we have an HETG model which is nearly accurate enough in the range 2200 - 9000 eV. At the lower energies of interest (400 eV - 2200 eV), however, the best fit grating model deviates from the synchrotron data by more than a few percent on average. In this paper we describe the model, the synchrotron tests that verify it, the discrepancies that we find at lower energies, and our plan to resolve the problems.

The high energy transmission grating spectrometer (HETGS) of the Advanced X-Ray Astrophysics Facility (AXAF) will include 336 gratings, of period 2000 angstrom and 4000 angstrom. The flight gratings have entered production, and preliminary tests for verification and calibration have begun. We present the current status of the x-ray tests at MIT, focusing on diffraction efficiency measurements and a grating tilt test. We indicate the direction the x ray testing will take in the near term.

This work presents the first results of our development of normal-insulating-superconducting tunnel junctions used as energy dispersive detectors for low energy particles. The device described here is a Ag/Al₂O₃/Al tunnel junction of area 1.5 multiplied by 10⁴ micrometer squared with thicknesses of 200 nm for the normal Ag strip and 100 nm for the superconducting Al film. Two different high-speed SQUID systems manufactured by quantum magnetics and HYPRES, respectively, were used for the readout of this device. At 80 mK bath temperature we obtained an energy resolution DeltaE_FWHM equals 250 eV for 5.89 keV x rays absorbed directly in the normal metal. This energy resolution appears to be limited in large part by the observed strong position dependence of the device response.

Andromeda is a wide-field, imaging, hard x-ray/soft gamma-ray instrument capable of detecting gamma-ray bursts (GRBs) a factor approximately 20 times fainter than GRO/BATSE. During one-year of a two-year mission, it could determine whether GRBs are Galactic or cosmological in origin by searching for an excess of bursts towards the nearby Andromeda galaxy (M31). As a pointed, imaging instrument with sensitivity in the 10 - 200 keV band significantly better than previous coded-aperture instruments, Andromeda is capable of carrying out important secondary science objectives: for example, studying the soft-gamma- repeater and x-ray transient populations of M31 and the Galactic bulge. Andromeda is a coded aperture gamma-ray telescope consisting of a hexagonal coded mask coupled to an alkali- halide imaging scintillation detector, a flight-proven technology adapted from the balloon- borne Caltech gamma-ray imaging payload (GRIP). The new instrument is optimized for the 10 - 200 keV band and has 1.5 degree angular resolution over a 17 degree FWHM field of view. Andromeda is designed to be a small, low-cost mission, and draws its design largely from existing instrumentation. Andromeda was submitted to the STEDI program, and will also be proposed as a NASA Small Explorer.

We report the first performance measurements of a sub-millimeter CdZnTe strip detector developed as a prototype for space-borne astronomical instruments. Strip detector arrays can be used to provide two-dimensional position resolution with fewer electronic channels than pixellated arrays. Arrays of this type and other candidate technologies are under investigation for the position-sensitive backplane detector for a coded-aperture telescope operating in the range of 30 - 300 keV. The prototype is a 1.4 mm thick, 64 multiplied by 64 stripe CdZnTe array of 0.375 mm pitch in both dimensions, approximately one square inch of sensitive area. Pulse height spectra in both single and orthogonal stripe coincidence mode were recorded at several energies. The results are compared to slab- and pixel-geometry detector spectra. The room-temperature energy resolution is less than 10 keV (FWHM) for 122 keV photons with a peak-to-valley ratio greater than 5:1. The response to photons with energies up to 662 keV appears to be considerably improved relative to that of previously reported slab and pixel detectors. We also show that strip detectors can yield spatial and energy resolutions similar to those of pixellated arrays with the same dimensions. Electrostatic effects on the pulse heights, read-out circuit complexity, and issues related to design of space borne instruments are also discussed.

We are studying a Next Generation X-ray Observatory, NGXO, that will provide a high resolution spectral capability with large collecting area, at a relatively low cost. The mission consists of two co-aligned telescope systems that provide coverage from 0.3 - 60 keV. One is optimized to cover the 0.3 - 12 keV band with 2 eV spectral resolution using an array of quantum calorimeters with a peak effective area of 2,000 cm². The spectral resolution will be five times better than the calorimeter planned for Astro-E, with more than a ten-fold increase in effective area over previous high resolution x-ray spectroscopy missions. The second telescope will be the first focusing optics to operate in the 10 - 60 keV energy range, and will have arc minute angular resolution with 500 cm² collecting area at 30 keV. The sensitivities of the two telescopes are matched to make possible many thousands of high quality x-ray spectral observations, from an available population of more than one million galactic and extragalactic x-ray sources. The NGXO mission is capable of addressing new astrophysical problems which include: determining the mass of a black hole, neutron star, or white dwarf in binary systems from x-ray line radial velocity measurements; determining the 0.3 - 60 keV x-ray spectrum from AGN and determining their contribution to the x-ray background in this energy band; measuring Compton reflection spectra from cold material in accretion driven systems; determining the Hubble constant using resonant line absorption of QSO spectra by rich clusters; searching for a hot 10 million degree intergalactic medium; mapping the dynamics of the intracluster medium; mapping the ionization state, abundance and emission from supernova remnants on a 15 arc second angular scale; and measuring mass motion in stellar flares and the dynamics of accretion flows.