The X-ray detection system used to calibrate the Advanced X-ray Astrophysics Facility (AXAF) mirrors will include gas flow and sealed proportional counters. To meet the ultimate 1 percent goal of the calibration project, the transmission and uniformity of the windows must be well known for the soft X-ray wavelengths involved. Various window materials for use with proportional counters are examined for transmission at X-ray wavelengths in the range of 0.1 to 5.9 keV. These include the usual window materials (polypropylene and beryllium), as well as materials only recently employed for detector applications (polyimide and diamond). The transmission uniformity of beryllium at 1.49 keV is examined with a microchannel plate detector, producing a 'shadowgraph' of the window material illuminated with soft X-rays. This technique allows us to investigate nonuniformities on a spatial scale of about .2 mm.

The design and performance of imaging gas scintillation proportional counters (IGSPCs) developed for ASTRO-D are described. The 10 micrometers beryllium window has enabled the x- ray sensitivity down to 0.7 keV for a sealed-off gas counter, and a position-sensitive phototube equipped with multiwire anode gives good imaging capability. The laboratory model of the IGSPC shows an energy resolution 8% FWHM at 6 keV and a position resolution 0.5 mm FWHM with an effective area of 50 mm diameter. The onboard data system incorporating a 16-bit microprocessor efficiently discriminates the room background down to the order of magnitude of 3 X 10-4 cm-2 s-1 keV-1, similar to that achieved by the Ginga LAC instrument. These performances make the GIS experiment a very powerful focal plane instrument for ASTRO-D.

The characteristics of a conventional cylindrical geometry proportional counter filled with high pressure xenon gas up to 10 atm. were fundamentally investigated for use as a detector in hard X-ray astronomy. With a 2 percent methane gas mixture the energy resolutions at 10 atm. were 9.8 percent and 7.3 percent for 22 keV and 60 keV X-rays, respectively. From calculations of the Townsend ionization coefficient, it is shown that proportional counters at high pressure operate at weaker reduced electric field than low pressure counters. The characteristics of a parallel grid proportional counter at low pressure showed similar pressure dependence. It is suggested that this is the fundamental reason for the degradation of resolution observed with increasing pressure.

Methods have been developed to make ultrathin low-leak x-ray entrance windows which can withstand atmospheric pressures. The first prototypes have been 6 mm or 20 mm diameter windows with film thicknesses 0.5 micrometers - 2.5 micrometers of polyimide and 40 nm - 100 nm of aluminum. Also 0.5 micrometers - 1 micrometers thick beryllium windows with diameter of 6 mm have been fabricated. The goal is to fabricate 140 mm and 70 mm diameter windows for Danish-Finnish position sensitive proportional counters to be flown on the Soviet SPECTRUM-ROENTGEN-GAMMA satellite.

Prototype ICs for the Solar Heliospheric Observatory's Multi-Anode Microchannel Array (MAMA) have been developed; these ICs' charge-amplifier and comparator components were then tested with a view to pulse response and noise performance. All model performance predictions have been exceeded. Electrostatic discharge protection has been included on all IC connections; device operation over temperature has been consistent with model predictions.

The Multi-Anode Microchannel Array (MAMA) is a photon counting detector which utilizes a photocathode for photon to electron conversion, a microchannel plate (MCP) for signal amplification and a proximity focused anode array for position sensitivity. The detector electronics decode the position of an event through coincidence discrimination. The decoding algorithm which associates a given event with the appropriate pixel is determined by the geometry of the array. A new algorithm incorporated into a CMOS Application Specific Integrated Circuit (ASIC) decoder which improves the pixel spatial resolution is described. The new algorithm does not degrade the detector throughput and does not require any modifications to the detector tube. The standard MAMA detector has a pixel size of 25 x 25 square microns, but with the new decoder circuit the pixel size is reduced to 12.5 x 12.5 square microns. We have built the first set of decode electronics utilizing the new ASIC chips and report here on the first imaging tests of this system.

Size reduction of two new multi-anode microchannel array (MAMA) readout systems is described. The systems are based on two analog and one digital application specific integrated circuits (ASICs). The new readout systems reduce volume over previous discrete designs by 80 percent while improving electrical performance on virtually every significant parameter. Emphasis is made on the packaging used to achieve the volume reduction. Surface mount technology (SMT) is combined with modular construction for the analog portion of the readout. SMT reliability concerns and the board area impact of MIL SPEC SMT components is addressed. Package selection for the analog ASIC is discussed. Future sytems will require even denser packaging and the volume reduction progression is shown.

We report on the development of a new high-dynamic-range two-stage Multi-Anode Microchannel Array (MAMA) imaging tube designed for improved high count rate performance at FUV and EUV wavelengths. The new two-stage MAMA tube employs two 25-mm-diameter format MCPs placed in tandem with a small gap between the plates. The front (input) MCP is designed to be a low-gain converter plate that supports an opaque photocathode and converts the detected photons to electrons, while the second (output) MCP is of higher conductivity and thus maintains the overall gain of the multiplier at high count rates. The second MCP is mounted in proximity focus with a (224 x 960)-pixel fine-fine coincidence MAMA array for high-spatial-resolution imaging studies. The applied voltage across each MCP can be controlled independently. We report on the gain and dynamic range performance characteristics of the two-stage MAMA tube in two different configurations: first, with the output MCP having moderate conductivity (about 100 MOhm); and second, with the output MCP having very high conductivity (about 2 MOhm). These results are compared and contrasted with those of the more conventional MAMA tube configuration which employs a single high-gain curved-channel MCP.

Results are presented from an evaluation of three sets of low resistance microchannel plate (MCP) stacks; the tests encompassed gain, pulse-height distribution, background rate, event rate capacity as a function of illuminated area, and performance changes due to high temperature bakeout and high flux UV scrub. The MCPs are found to heat up, requiring from minutes to hours to reach stabilization. The event rate is strongly dependent on the size of the area being illuminated, with larger areas experiencing a gain drop onset at lower rates than smaller areas.

The observed counting rates of microchannel plate (MCP) based detectors for high resolution observations of celestial EUV and X-ray sources vary over many orders of magnitude; the counting capability of an individual channel, however, is not high, and is associated with dead-times ranging from 0.1 msec to 1 sec. The dead-time increases with the area illuminated; attention is presently given to laboratory determinations of the count rate characteristics of a MCP detector as a function of illuminated area, and a model is developed for these results' use in the interpretation of space observations.

A novel low energy astronomical gamma-ray detector is being developed for future satellite missions. Recent advances in the technology of photodiodes and small, low noise amplifier circuits have meant that more compact detectors can be assembled in a complex array in order to give a 3-D position reconstruction capability. In a mask-detector telescope this capability is potentially very useful since it allows the reconstruction of the path of the incident gamma rays making it valuable both for imaging and background rejection. A small prototype of a 3-D detector has been realized for test in a balloon mission. The detector is based on a 12 X 8 array of position sensitive CsI(T1) bars, typically 15 cm long with 1.3 X 1.3 cm cross section, viewed at each end by photodiodes. The detector includes four 1.3 X 1.3 X 2.5 cm CsI(T1) scintillators located above the main array in order to evaluate the low energy response of the imager. The detector constitutes an active block of 2400 cm3 of scintillator that can operate in the 0.2 - 10 MeV energy range. The energy resolution is 13% at 662 keV and the positional resolution is of the order of 1.5 cm in each dimension. An active shield of CSI(T1) and plastic scintillators surrounds the bar detector. The overall experiment is briefly described in general and preliminary results of laboratory tests are presented.

Hard x-ray reflectivity measurements of mosaic crystals are being performed at the x-ray facility of the physics department of the University of Ferrara. This paper reports on preliminary results obtained by using flat samples of pyrolytic graphite (002) with a thickness of 2 mm and a mosaic spread of 0.3 deg. A short description is given of the experimental apparatus and calibration procedures followed.

Results are reported from an effort to define a passive magnetic field concept for the High Energy X-ray Timing Experiment (HEXTE), in the interest of reducing the detector-gain variations due to 0.5-1.0-sec timescale magnetic field variations. This will allow a sensitivity of the order of 1 percent of the HEXTE background. While aperture modulation and automatic gain control will minimize effects on timescales of tens of seconds and longer, passive magnetic shielding of the photomultiplier tubes will address 1-sec timescale variations due to aperture motions.

The High Energy X-Ray Timing Experiment (HEXTE), currently under development for the X-Ray Timing Explorer (XTE) mission, employs a closed loop gain control system to attain 0.5 percent stabilization of each of eight-phoswich detector gains. This Automatic Gain Control (AGC) system utilizes a split window discriminator scheme to control the response of each detector pulse height analyzer to gated Am-241 X-ray events at 60 keV. A prototype AGC system has been implemented and tested within the gain perturbation environment expected to be experienced by the HEXTE instrument in flight. The AGC system and test configuration are described. Response, stability and noise characteristics are measured and compared with theoretical predictions. The system is found to be generally suitable for the HEXTE application.

Soft x-ray filter designs for the Brigham Young University `Goldhelox Project' are discussed. Three polymers intended for use as a supportive substrate for a soft x-ray solar filter having a passband centered at 171 angstroms are examined. The use of polymer substrates is examined because of vibrational and mechanical stresses associated with the shuttle launch, preventing the use of a free standing filter, and because of Goldhelox's special need to locate the filter near the imaging plane. The uniform consistency of a polymer support prevents any imaging of the filter support structure, as would occur if a traditional mesh support were used. The polymer substrates investigated are: AP-1, Formvar, and polypropylene. Their transmissive characteristics of the polymers are examined along with the feasibility of their use. Transmission as a function of energy for each polymer is given over an energy range of 10 to 180 eV.

Several approaches to imaging hard X-rays emitted from solar flares have been proposed or are planned for the nineties including the spatial modulation collimator (SMC) and the rotating modulation collimator (RMC). A survey of current solar flare theoretical literature indicates the desirability of spatial resolutions down to 1 arcsecond, field of views greater than the full solar disk (i.e., 32 arcminutes), and temporal resolutions down to 1 second. Although the sun typically provides relatively high flux levels, the requirement for 1 second temporal resolution raises the question as to the viability of Fourier telescopes subject to the aforementioned constraints. A basic photon counting, Monte Carlo 'end-to-end' model telescope was employed using the Astronomical Image Processing System (AIPS) for image reconstruction. The resulting solar flare hard X-ray images compared against typical observations indicated that both telescopes show promise for the future.

The `Goldhelox' project (`GOLD' for the color of the sun and `HELOX' for heliocentric observations in x rays) includes a student run research team, involving more than 30 volunteer students and five advising professors, to design and build a project to obtain observations of the sun in x rays by using the Space Shuttle as a platform while situated in a NASA Get-Away Special (GAS) canister. The GAS program allows universities, companies, and others to send small self-contained experiments into space in canisters that are placed in the Shuttle's cargo bay. The main scientific objective is to construct a high-resolution soft x-ray telescope to take rapid succession, full disk pictures of the sun, hopefully during Solar Max. These images will help in the understanding of such solar features as the corona, flares, and chromosphere. The project is organized into four major groups. The Flight Readiness Team is in charge of testing, quality control, all safety aspects, and NASA documentation. The optics system is being designed and built by the Optics Team, and this includes the telescope that has curved- substrate, multilayer mirrors, an x-ray filter, a microchannel plate (MCP) detector, a phosphor screen, a fiberoptic plate, and a customized camera that uses ordinary film. The motors for driving the telescope in two axes, worm drives, sealed container for the electronics and batteries, and the overall structure are part of the Mechanical Team. The Electrical Team's responsibilities include the photodiode sun sensor, a small heater for environmental control, lead-acid gel batteries, the main data collecting computer, telescope controller, supporting electronics, and electrical feedthroughs. This project should increase knowledge in the area of x-ray optics and spaced-based physics.

The HEXTE, part of the X-Ray Timing Explorer (XTE), is designed to make high sensitivity temporal and spectral measurements of X-rays with energies between 15 and 250 keV using NaI/CsI phoswich scintillation counters. To achieve the required sensitivity it is necessary to provide anticoincidence of charged cosmic ray particles incident upon the instrument, some of which interact to produce background X-rays. The proposed cosmic ray particle anticoincidence shield detector for HEXTE uses a novel design based on plastic scintillators and wavelength-shifter bars. It consists of five segments, each with a 7 mm thick plastic scintillator, roughly 50 cm x 50 cm in size, coupled to two wavelength-shifter bars viewed by 1/2 inch photomultiplier tubes. These segments are configured into a five-sided, box-like structure around the main detector system. Results of laboratory testing of a model segment, and calculations of the expected performance of the flight segments and particle anticoincidence detector system are presented to demonstrate that the above anticoincidence detector system satisfies its scientific requirements.

X-ray interferometry has the potential for observations of unprecedented angular resolution and far-reaching astrophysical consequences. A new concept for an x-ray interferometric observatory that obtains an angular resolution 105 times better than AXAF is presented. Using a grazing incidence fringe spectrum design, the x-ray interferometer operates over a broad band (0.2 - 8 keV), with on the order of magnitude 18 concentric Wolter-Schwarzschild mirror shells of diameter 0.6 - 2.4 m. A fringe-sensitive detector measures the closely spaced Fizeau fringes in the focal plane. Fringe phasing is maintained using an optical metrology system and two optical Michelson stellar interferometers to provide absolute inertial reference for the phase tracking center. Mirror phasing is maintained with active control of low spatial frequency figure errors. The interferometer is capable of obtaining detailed images of nearby stellar coronae, imaging the broad-line regions and jets of many AGNs, and resolving the accretion disks of a selection of bright AGNs and QSOs.

Imaging Extreme Ultraviolet (EUV) Multi-Anode Microchannel Array (MAMA) detector systems with formats of 360 x 1024 pixels and pixel dimensions of 25 x 25 sq microns are being fabricated and tested for flight in two instruments on the ESA/NASA Solar and Heliospheric Observatory (SOHO). In addition, very-large-format (1024 x 1024)- and (2048 x 2048)-pixel Far Ultraviolet (FUV) and EUV MAMA detectors with pixel dimensions of 25 x 25 sq microns are being fabricated and tested for use in the NASA Goddard Space Flight Center's Hubble Space Telescope Imaging Spectrograph (STIS), a second-generation instrument scheduled for in-orbit installation in 1997. Finally, FUV MAMA detectors with formats of 224 x 960 pixels and pixel dimensions of 14 x 14 sq microns are being evaluated as prototypes of the detector for the prime FUV spectrograph of the Far Ultraviolet Spectroscopic Explorer (FUSE/Lyman) mission. The configurations and performance characteristics of the different detector systems are described, and the plans for further development of the Advanced Technology MAMA detector system discussed.

Photometric imaging of ionospheric/magnetospheric O II emission at 83.4 nm is a primary objective for mapping the distribution of O(+) ions. However, instrumental sensitivity has been a major barrier to realizing this goal. We report an instrumental design employing a low focal ratio three-mirror camera where the reflecting surfaces act as both narrowband reflection filters at 83.4 nm and as a high quality imaging system. The design includes coatings with reflectances that are relatively insensitive to the angle of incidence of light. The peak reflectance per mirror is more than 60 percent at 83.4 nm with the average reflectance for out-of-band wavelengths of less than 5 percent. The net reflective transmission for the three mirrors is greater than 20 percent with 6.8 nm bandwidth and 0.01 percent maximum transmittance for out-of-band wavelengths. The transmittance at 30.4 nm is 0.03 percent at 58.4 nm 0.05 percent, and at 121.6 nm 0.004 percent. When used with an open microchannel plate detector, contamination by H Ly-alpha is essentially eliminated. With this spectral purity and effective elimination of major contributors to background contamination noise, a signal-to-noise ratio (excluding detector noise) of 10 is achievable for a 0.01 R signal in 8.8 seconds for the full 6 deg field-of-view.

The Silicon X-ray array, or 'SIXA' detector experiment will be carried by one of the 8-m focal length X-ray telescopes of the Spectrum-X-Gamma satellite. SIXA, which will measure X-ray spectra at good resolution simultaneously with the other X-ray telescope's gathering of images, uses 19 discrete, circular and closely packed Si(Li) detectors with an estimated resolution of 170-180 eV at 6 keV. The electronics of the SIXA instrument uses 19 parallel amplifier channels.

Recent developments in the manufacture of GaAs detectors for high energy physics applications and dark matter searches have resulted in working devices made from LEC and HB starting material This offers the promise of routine manufacture of reproducible devices at a modest cost. The most advanced of the techniques is that of Schottky diodes on LEC material. Results are presented demonstrating the performance of such devices (3.0 mm X 5.0 mm X 200 micrometers ) as x-ray detectors, including their low temperature operation. An alternative technique using charge collection in bulk HB material at temperatures down to liquid helium also is briefly described.

Two types of drift device, namely photodiodes and position sensitive drift chambers with segmented anode and cathode structures, have been studied at room temperature and below. Leakage current and electron mobility have been investigated at low temperature for the drift photodiodes. Self-triggering has been achieved for the position sensitive drift chambers using 60 keV photons, and differences in arrival time between the prompt trigger signal from the cathode and the delayed anode signal have been studied as a function of drift distance and temperature. The response of the photodiodes when coupled to a CsI scintillator at room temperature has been assessed.

Silicon bolometers are currently under development for milliKelvin operation; these devices are being produced using Si wafer fabrication technology. The design and performance of individual bolometers, using doped layers with a thickness in the range 0.1 to 3 (mu) , are described. The use of epitaxial growth to replace ion implantation for improved performance is described and initial results reported.

X-ray detectors based on superconducting tunnel junction technology are desirable due to their potential for higher energy resolution and greater charge carrier production than conventional semiconductor devices. Single junction devices fabricated by thermal or plasma oxidation of elemental, soft metal, superconductors have shown some promise, but tend to suffer from poor opacity, performance degradation upon thermal recycling, and unequal total charge collected for absorption of x rays in different layers due to differing tunneling characteristics of each layer. More complex designs, such as quasi-particle trapping systems and all refractory materials, can help with the unequal charge and thermal cycling problems, respectively. However, new problems in complexity of fabrication and short quasi-particle lifetimes arise. Other potential difficulties include resolution degradation due to trapping of quasi-particles at the photoabsorption site or near defects and tolerance of the devices to faults induced by their environment. The use of multilayers of superconducting tunnel junctions, consisting of tens to hundreds of identical tunnel junctions stacked on top of one another, as a design can address these problems. The multilayer can, in principle, be made as thick as desired in order to increase opacity, while the individual superconducting layers can be made very thin in order that the tunneling time of the quasi-particles be short compared with the quasi-particle lifetime for even refractory superconductors. In addition, the layer thinness helps to alleviate undesirable quasi-particle trapping. The inherent redundancy of junctions in a multilayered device allows for continued operation even after multiple single layer failures. The unique physical and technological possibilities of multilayered devices, such as resonant tunneling and built in preamplification, make them structures worthy of study even without the more pragmatic inducements described above.

We discuss a high resolution microchannel plate (MCP) imaging detector to be used in measurements of Doppler-shifted hydrogen Lyman-alpha line emission from Jupiter and the interplanetary medium. The detector is housed in a vacuum-tight stainless steel cylinder (to provide shielding from magnetic fields) with a MgF2 window. Operating at nominal voltage, the four plate configuration provides a gain of 1.2 x 10 exp 7 electrons per incident photon. The wedge-and-strip anode has two-dimensional imaging capabilities, with a resolution of 40 microns FWHM over a one centimeter diameter area. The detector has a high quantum efficiency while retaining a low background rate. A KBr photocathode is used to enhance the quantum efficiency of the bare MCPs to a value of 35 percent at Lyman-alpha.

Requirements for spaceflight optical instruments usually dictate that for the structures be rigid, lightweight, and thermally stable. In addition, for interferometric far ultraviolet (FUV) spectrometers, the requirements for torsional deflection are more severe than with conventional spectrometers. To meet the challenge for rigid and lightweight optical instruments, this paper explores the design of a high-stiffness structure for the support of an FUV spatial heterodyne interferometer where the torsional deflection of the instrument is on the order of 10 arc seconds. The structure is based on use of a thin, hollow section beam with weight-relieving between optical elements. The design also uses a modular and self-contained positioning mechanism that is removed after final optical alignment. Several specific material properties are presented as criteria for material selection. The parameters which affect the particular design requirements are identified with respect to the desired material properties and physical design features. Although large thin sections are susceptible to thermal gradients, this could be minimized by a trade-off for weight, where adequate margin exists. This paper describes the preliminary design for the structure and presents an analysis to verify compliance with the requirements.

Spaceflight optical instruments have two conflicting requirements. They need to be both rigid and lightweight. In addition, for interferometric far ultraviolet spectrometers, the requirements for precision positioning are more severe than for conventional spectrometers. To meet the challenge of lightweight optical instruments, a modular adjustment mechanism was developed to position two orthogonal axes of a universal three-axis gimbal support system with a positioning accuracy on the order of 10 arc seconds. The mechanism was designed as a self-contained assembly which can be removed after final alignment of a spacebound optical instrument to reduce its in-flight mass. To demonstrate the concept, a number of these assemblies were made and mounted on two of the positioning axes of a far ultraviolet spatial heterodyne interferometer. A shaft clamp was used on each positioning axis to retain the adjusted position. This paper describes the design of the mechanism and presents optical test results.

A need has arisen for efficient, blazed, symmetric gratings for use as beam splitters in far and extreme ultraviolet interferometers. In particular, the development of an all-reflection, far ultraviolet spatial heterodyne interferometer can benefit tremendously from such a grating. To fulfill this need, we have manufactured a mechanically ruled grating with a V-groove profile blazed for H Lyman-alpha at 1216 A. We present the grating performance at Lyman-alpha in the context of its application to the spatial heterodyne interferometer.

PN-CCDs are being developed as focal plane detectors for ESA's X-ray Multi-Mirror satellite mission (XMM), to be launched at the end of this century. As a part of the European Photon Imaging Camera (EPIC) the pn-CCDs will convert the incoming X-ray radiation with high quantum efficiency, low readout noise, excellent background rejection, timing in the microsec regime, radiation tolerance up to several hundreds of krads and a position resolution tailored according to the angular resolution of the telescope. The goal of our laboratorial efforts for this mission is to fabricate a monolithic pn-CCD of an active area of 6 x 6 sq cm having 768 on-chip JFET amplifiers located at the end of each CCD line. It is the aim of this contribution to report on the ongoing work of the pn-CCD system. This article focuses on the position resolution capabilities of fully depleted pn-CCDs, some recent results in the noise analysis and preliminary results on 10 MeV proton damage.

The properties of niobium superconducting tunnel junctions as x-ray detectors are investigated. The charge output, which depends on the geometry of the system, is severely reduced by self recombination in small size junctions and the specific characteristics of the barrier. These loss mechanisms, coupled with another energy loss mechanism due to phonon propagation into the substrate, cause additional variances on the charge output, which degrade the energy resolution.

The two co-aligned x-ray imaging telescopes in the JET-X instrument on Spectrum R-G use passively cooled x-ray sensitive CCDs in the focal plane imagers. Development of the CCD for JET-X, the design and performance of the focal plane assembly are reviewed and improvements to both the low energy and high energy quantum efficiency are described. Performance data on spatial and energy resolution, and the rejection efficiency to charged particle background, obtained with prototype CCDs, are presented.

An all-reflection spatial heterodyne spectrometer (SHS) has been recently developed. The advantages over conventional high-resolution grating spectrometers are that the SHS requires no mechanical scanning, a self-compensating optical design permits easy alignment, and it is much smaller than other spectrometers of comparable resolution. Since all beam-splits and recombinations occur by reflection off of a diffraction grating, the interferometer is capable of operating well into the extreme ultraviolet (EUV) and possibly into the soft X-ray region. A description of the design and the characteristics of the instrument is presented. Also, test results, including sample interferograms as well as their Fourier-transformed spectra, at both visible and UV wavelengths are shown. Finally, we report on future developments and possible applications.

A novel, fledgling approach to the filtering of EUV radiation for laboratory and space applications is reviewed. Foils perforated by a set of parallel channels with submicron diameters serve as wavelength-dependent filters. Each channel passes photons when the wavelength is much smaller than the channel diameter. The transmission of the channel drops dramatically, however, when the wavelength becomes comparable to or larger than the channel diameter. The relevant theoretical considerations as well as available experimental data are presented. Several different ways to manufacture such kind of filters are outlined, including nuclear track filters, anodized metal films, and microchannel plate technology. Advantages and disadvantages of each technique are discussed. The history of the work in the field as well as prospects for the future are presented.

The X-ray detection system used to calibrate the Advanced X-ray Astrophysics Facility (AXAF) mirrors will include gas flow and sealed proportional counters. To meet the ultimate 1 percent goal of the calibration project, the transmission and uniformity of the windows must be well known for the soft X-ray wavelengths involved. Various window materials for use with proportional counters are examined for transmission at X-ray wavelengths in the range of 0.1 to 5.9 keV. These include the usual window materials (polypropylene and beryllium), as well as materials only recently employed for detector applications (polyimide and diamond). The transmission uniformity of beryllium at 1.49 keV is examined with a microchannel plate detector, producing a 'shadowgraph' of the window material illuminated with soft X-rays. This technique allows us to investigate nonuniformities on a spatial scale of about .2 mm.

A Bragg Crystal Spectrometer (BCS) using a gas flow proportional counter as its primary detector is among the instruments under development for AXAF. The BCS will employ windows of 1-micron-thick polyimide coated on both sides with 200 A of Al; this window composition, while X-ray transmitting, will leak gas at a lower rate than the polypropylene film-based windows formerly employed. Accounts are given of the results obtained with additional innovative X-ray window materials currently under development, including diamond and Si-enriched Si3N4.

The X Ray Multimirror Mission will include a spectrometer consisting of two arrays of variable line-spaced reflection gratings for use in the 350 eV to 2.5 keV energy range. Approximately 720 replica gratings will be needed for two flight grating arrays and one spare. Evaluation of potential master gratings to be used in the replication process has begun. Both reflectivity and scattering x-ray measurements for three mechanically ruled prototype master gratings have been reported.

Remote sensing of resonantly scattered 304 angstrom sunlight by He+ in the earth's plasmasphere would provide a structural map of the plasmasphere. The primary concern for such an imaging system is the extraction of the 304 angstrom signal out of a background of other wavelengths of much higher intensities. The capability of multilayer mirrors and thin film filters for this task are analyzed and some guidelines for the design of these optical elements for space imaging applications are presented. Analysis shows that multilayer mirrors require the use of a filter to remove longer wavelength background emissions and they do not provide uniform reflectance over the desired 30 deg field of view. An effective and simpler alternative for this application may be a Si coated Te transmission filter without multilayer mirrors.

DSRI will provide a set of four imaging proportional counters for the Danish-Soviet X-ray telescopes XSPECT/SODART. The sensor principle is based on the novel micro-strip proportional counter (MSPC), where the strip electrodes are deposited by photolithography onto a rigid substrate. The MSPC offers many advantages : A uniform gas gain, an excellent energy resolution, the possibility to match the strip pitch to the desired positron resolution, a fast charge collection and low operating voltages. However, a stable behaviour of the MSPC requires a careful choice of both substrate and strip electrode material. The low energy detectors will be equipped with polyimide windows of 0.5 pm thickness, providing a high quantum efficiency even at 200 eV with an energy resolution comparable to that of solid state detectors. The MSPC is capable of operating at high counting rates (iO ph s1) and the electronics is designed to match this capability.

In the past decade, gas scintillation proportional counters (GSPCs) have proved their reliability and usefulness in space applications. The combination of high quantum efficiency over a wide energy range, large effective area, good spectral resolution, and high time resolution has given GSPCs a special role in x-ray astronomy. A wide variety of possible configurations makes matching of particular requirements possible. An exact understanding of the physics involved is essential for the further improvement and precise calibration of GSPCs. This paper shows that synchrotron radiation sources, with their continuously variable energies, fluxes, and collimation, provide the ideal tool by which to study the physical processes occurring in GSPCs as well as being perfectly suited for the calibration of such instruments.