SAX will contain six instruments of which two will be Wide Field X-ray Cameras. Their design is based on the coded mask principle, mask and detector size are equal. We argue that this 'simple' camera design has certain advantages compared with the 'optimum' cameras where complete coding is pursued. The Field Of View (FWHM) is 20 degrees square, the angular resolution 5 arcminutes and the energy band ranges from 1.5 to 32 keV. The detector is a Multi Wire Proportional Counter with an area of 25.6 x 25.6 cm², the position resolution is better than 0.5 mm. The mask pattern is based on a pseudo random array that has in principle ideal imaging capabilities. We show that the imaging imperfections due to incomplete coding can mostly be corrected for with image reconstruction techniques.

Historical citations concerning the origins of coded-aperture imaging are corrected. Another scheme is presented for synthetic indirect imaging to overcome certain shortcomings of simple coded apertures. Pairs of Fresnel zone patterns are used to create moire patterns that can be Fourier transformed for image reconstruction. It is also conjectured that image reconstructions that are constrained to be nonnegative should overcome certain complaints concerning indirect imaging.

The development of thin plastic scintillating fibers has opened the way to new designs for detectors in gamma ray spectroscopy and imaging. Monte Carlo simulation of these scintillating fiber detectors can provide important data for their use in designs of gamma ray telescopes and medical imagers. Results will be presented for different detector designs using 0.25 mm to 1 mm wide scintillation fibers for gamma ray energies between 0.5 and 50 Mev. These simulations show the significant improvements which can be achieved by applying this type of detectors in gamma ray astronomy and medical imaging.

Several imaging spectrometers, involving three distinct rotation modulation collimator designs, have been simulated on a computer. Data produced by the Monte-Carlo technique were used to reconstruct images using the method of rotational aperture synthesis'. Common to all the simulations were the use of nonposition-sensitive detectors, cylindrical collimator geometry, data accumulation over 360°, and grids producing consecutive harmonics of the lowest spatial frequency. The statistical behavior of 'simple and complex images were studied including the noise produced by the reconstruction method and by the detector background. Aberrations or artifacts were produced by the following: variations of detector efficiency, misalignment of the instrument and rotation axes, time varying backgrounds, parallax (as encountered in laboratory testing), and using only one detector of each frequency pair. Methods were devised to eliminate each of these aberrations or artifacts; most of these methods are exact and do not increase the background noise. To determine the optimum number of detectors to use for a given total area, the reconstructed image of a single point was studied as a function of resolution. If, for a constant flux, one expands the image field proportional to the number of detectors used, the peak height, peak width, sidelobe structure, and background characteristics remain unchanged within statistics. Thus, this method imposes no constraint on resolution; rather, geometry and instrument complexity determine the practical limit.

We are constructing a telescope with arcminute resolution in the soft 7-ray band. This telescope will provide the first images of cosmic sources on arcminute scales in the energy range 30 - 200 keV. Arcminute resolution gives us the capability, for the first time, to image truly diffuse emission in this wavelength band, opening up exciting new scientific opportunities. The payload consists of ~36 independent coaligned modules. Each module consists of an alkali halide scintillating crystal collimated to a one dimensional coded aperture mask. Every module is fixed in the telescope with a different rotational orientation, allowing reconstruction of two dimensional images. For our application this novel approach has several advantages over a standard two dimensional coded aperture implementation. We have simulated this system and demonstrated the fidelity and robustness of the reconstructions. In addition, we have refined the GRATIS detector technology and achieved improved spatial resolution over that previously reported.

We present results from a prototype high pressure xenon gas scintillation drift chamber using a novel wave-shifter fiber readout scheme. We have operated the chamber at pressures as high as 20 atmospheres and have determined that the secondary light yield is linear in both reduced field and pressure. We have measured the primary scintillation light yield to be one photon per 76±12 eV deposited energy. We present initial results of our chamber for the two-interaction separation (<4 mm in the drift direction, mm orthogonal to the drift); for the position resolution (<400 gm rms in the plane orthogonal to the drift direction); and for the energy resolution (ΔE/E < 6% FVVHM at 122 keV).

The HEAO1 A4 satellite hard X-Ray sky survey, performed in the late '70s, has discovered a crowded and complex hard X-Ray sky in the range 10 180 keV. This intrigued scenario has been recently confirmed by high quality balloon borne experiments. These experiments in spite of their good spectral capability have been generally unable to provide good positional resolution and large sky coverage because of the use of passive collimators with wide field of view (f.o.v.) (typically 3 ÷ 15 degree). It is now evident the scientific need for a new generation of hard X-Ray instruments providing high imaging and spectral resolution over a wide energy range to study the spectral behaviour of different classes of cosmic sources and to identify these X-Ray emitters with their counterparts at optical, infrared and radio wavelenghts. In this note we will describe a new type of position sensitive MultiWire Proportional Counter (MWPC) recently designed and built at the prototype level in our Institute. This detector, expected to be fully operational in two years, will be assembled with a coded mask, employed as the imaging device, and flown on-board a balloon borne experiment as a high-resolutionwide-angle hard X-Ray telescope. The main scientific goal is to produce sky images in the range 15 + 180 keV with arcminute angular resolution, good spectral resolution (λ/Δλ=20) and milliCrab sensitivity, during a typical observation time of 10⁴ seconds. A space qualified version of this instrument operative in the range 2.5 ÷ 180 keV has been proposed on-board the Soviet mission "Spectrum X-Famma" expected to fly in the mid '90s.

The WINKLER spectrometer is a matrix of nine high-purity, n-type germanium detectors developed for astrophysical observations and terrestrial radiation monitoring. The spectrometer has been fitted with a set of modulation collimator grids designed for imaging hard x-ray and gamma-ray sources by the method of Mertz, Nakano, and Kilner. This technique employs a pair of gridded collimators in front of each detector with the number of grid bars varying from one to N, where N is the number of detectors. When the collimator pairs are rotated through a full 360 degree angular range, the detector signals provide the information for a two-dimensional band-limited Fourier reconstruction of order N. Tests of the spectrometer with single and multiple point sources as well as continuous source distributions are reported. The spectrometer field-of-view is 20 deg, and the observed FWHM of the point spread function is 1.6 deg, in good agreement with simulation results. Images have been obtained for gamma-ray energies from 60 keV to 1.3 MeV, although transmission through the grids reduces contrast at the higher energies. Potential capabilities of the spectrometer for locating the position of single point sources or resolving structure in closely-spaced source distributions are discussed, as well as proposed upgrades to improve angular resolution.

We have performed simple laboratory studies of several of the newer high-Z inorganic scintillators, with a primary goal of evaluating their relative merits as sensors for space-borne instruments. It is appropriate to consider using one of these materials when high light output can be exchanged for some other beneficial property, such as higher stopping power (bismuth germanate), superior resistance to radiation damage (barium fluoride), or fast decay time (barium fluoride and pure cesium iodide). Our work has revealed or confirmed other important characteristics both favorable and unfavorable of these newer scintillators. For example, the temperature dependence and particle species dependence of the fast and slow scintillation output of barium fluoride and pure cesium iodide will be described.

A gamma ray detector system, originally designed for the GRASP gamma ray telescope satellite, is being developed. It has the ability to determine the position of a single photon interaction in one plane to an accuracy of 15 mm, and with a precision of <20 mm FWHM in the third dimension. The total sensitive area of the GRASP detector is 1859 cm 2 .

We describe the design and performance of a charge coupled device (CCD) X-ray camera developed at Penn State. The camera uses an MIT Lincoln Labs frame-store CCD as the detector element. A laboratory version using a PC-based CCD controller and data acquisition system and a thermoelectric cooler has been completed and is being used for laboratory testing of the CCD. This is an extremely flexible system, with all clock waveforms and voltages, the operating temperature, and data acquisition and display under software control by the PC. Using this camera, we have measured read noise of less than 1.5 e- with the serial clocks running backwards to suppress dark current. The energy resolution at 5.9 keV with the CCD running in its normal configuration is 120 eV. The flexibility of the camera allows automated testing and parameterization of CCDs of arbitrary format. A flight version of this camera is also being built, and will be launched in late 1989 or early 1990 to make spectrally resolved images of the Puppis A supernova remnant.

The Reflection Grating Spectrometer (RGS) experiment on the X-ray Multi-Mirror (XMM) spacecraft will consist of two identical medium resolution ( ~100 - 560) reflection grating spectrometers operating in the 5-35 Å range.1 The dispersed X-ray beam will be detected by an array of 10 CCD's (nine for spectroscopy, one for wavelength and alignment calibration). This paper describes the requirements set upon CCD performance by this experiment as well as the first results obtained with a special test setup which has been designed as to allow optimum flexibility in changing all CCD parameters (clock sequences, slopes, bias voltages etc.) under software control.

A number of future space-borne X-ray astronomy missions have now been proposed, which will utilise CCD imaging devices in their focal planes. The CCDs will offer simultaneously high spatial resolution, excellent energy resolution and detection sensitivity. However, a number of technological developments are still to be demonstrated before the X-ray performance of CCDs is optimised. The development of CCDs fabricated on high resistivity silicon wafers, combined with back thinning and annealing processes, allows the production of fully depleted detectors. These devices are capable of detecting single X-ray photons , with high efficiency throughout the 0.1-15keV energy band. Efficient coverage of focal planes is facilitated with the introduction of new large area CCDs. The EEV P88000 series CCDs have a range of formats up to 1242 x 1152 pixels (6.5 sq cm), and have included process changes to optimise noise (5.5 electrons rms) and dark current. Results of a programme to investigate the tolerance of EEV CCDs to ionising radiation are also presented.

A large area, high sensitivity hard X-Ray experiment, operating in the energy range 15 = 300 keV, has been succesfully flown twice (1986 and 1987) from the balloon launching facility of Trapani-Milo (Sicily). This balloon borne multitechnique telescope was designed and built within the framework of an international collaboration between the Istituto di Fisica Cosmica and the Istituto di Astrofisica Spaziale, C.N.R., Italy and the Department of Physics of the Southampton University, U.K. The telescope consists of two different arrays; scintillation detectors(NaI 5.5 mm thick actively shielded) with a total area of 2,700 cm 2, and Multiwire Proportional Counters (MWPC) with a total sensitive area of 900 cm2. The scintillation detectors provide a large sensitive area over the energy range 20 300 keV, with moderate energy resolution, while the proportional counters cover the range 15 4. 130 keV with good spectral resolution (8% at 120 keV). During the two flights several cosmic sources have been observed and detected. Preliminary results will be presented on the Crab, used as an in-flight calibration source, and on the extragalactic objects 3C273, NGC 4151 and MCG 8-11-11.

The High Energy X-Ray Timing Experiment (HEXTE) is one of three x-ray instrument components on NASA's X-Ray Timing Explorer (XTE) mission to be launched in 1994 for the detailed, 2-200 keV study of bright x-ray pulsars and other x-ray sources through observations of their temporal variability. Through extensive, dedicated, pointed observations of these sources, XTE will directly address issues pertaining to the nature of compact matter (white dwarfs to massive black holes), the evolution of systems containing these objects, and the conditions of astrophysical plasmas in their vicinity under extreme conditions of gravity, magnetic fields, and temperatures. The HEXTE is composed of two clusters, each containing four NaI/CsI phoswich scintillation counters with a total net collecting area of 800 cm² per cluster. The detector system is designed to achieve state-of-the-art scintillator energy resolution (AEA 5. 0.1 @ 100 keV) and high spectral sensitivity (3 σ detection of 1 milliCrab active galaxy in one energy resolution element - Δ E = 20 keV - at 100 keV in 10⁵s). This high performance is achieved through the large area and controlling systematic uncertainties to be 0.001 of instrument background, by utilization of aperture modulation rapid with respect to instrument background variations, automatic gain control, and a small field of view (1° FWHM). Instrument control and data formatting is accomplished by an onboard microcomputer system, which can be configured to maximize the scientific return for each individual observation within the constraint of 5000 bits/s of allocated telemetry.

The Burst and Transient Source Experiment (BATSE), one of four experiments on the Gamma Ray Observatory (GRO), is expected to provide the most sensitive observations of γ-ray bursts yet obtained, as well as to provide long-term monitoring of hard x-ray and low-energy γ-ray emission from bright pulsating sources, transients, and solar flares. Eight uncollimated modules, positioned at the corners of the spacecraft to provide an unobstructed view of the sky, detect sources by various techniques based on time variability. Use of detectors with anisotropic response allows location of γ-ray bursts to be determined to an accuracy of s1° using BATSE data alone. The completed BATSE underwent intensive testing and calibration prior to its delivery in October 1988 for integration on the GRO. We describe the instrument and summarize the results of the testing and calibration as they relate to characterization of systematic uncertainties in BATSE btirst location.

Space-station Observer for Nuclear Gamma-ray Spectroscopy (SONGS) was proposed to NASA for the Space Station Attached Payloads Program. The instrument comprises an array of 19 two-segment, n-type Ge detectors providing high energy resolution with a total sensor area of 373 cm2. A rotational modulation collimator imaging system which can be deployed in and out of the nominal 15°F0V, provides a spatial resolution of 1.2°. Energy resolution of 1 keV at 100 keV and 2 keV at 1 MeV permits definitive identification of line spectra resulting from high energy processes at work in the cosmos. The 36 sensitivities limits of (3-8)106 photons/(cm2 s) are achieved for lines between 100 keV and 1-2 MeV, and a few times 10-7 photons/(cm2 s keV) for the continuum flux with exposure periods of 106 s. In addition, the close-packed Ge sensor array provides a natural sensitivity for the measurement of gamma ray polarization in the 100 keV to 1 MeV energy range. Such polarization data should yield important information relating to the structure of the magnetosphere of neutron stars and of the accretion disk of black holes. The entire instrument will be mounted on a two-axis pointing system with the capability to fix on a target source independent of the Space Station orientation. A quick response for the pointer will allow observations of transient events. A massive (-270 kg), multi-segmented, NaI shield surrounding the Ge detectors is designed to recognize a gamma-ray burst or a solar flare event and to determine its source direction to about 2-3° which is precise enough to direct the pointer well within the 15° FOY of the Ge detectors. The SONGS spectrometer is a derivative of the Advanced Nuclear Gamma-ray Analysis System (ANGAS), the design of which is essentially complete and ready for production. The Space Station is an ideal platform to perform gamma-ray astronomy since it accommodates large payloads, permits long term observations, and orbits in a relatively low background environment by virtue of its low altitude and low inclination angle.

We are developing a Monitoring X-Ray Experiment (MOXE) for the Soviet Spectrum-X-Gamma Mission. MOXE is an X-ray all-sky monitor based on array of pinhole cameras, to be provided via a collaboration between Goddard Space Flight Center and Los Alamos National Laboratory. Our objectives are 1) to alert other observers on Spectrum-X-Gamma and other platforms of interesting transient activity, and 2) to synoptically monitor the X-ray sky and study long-term changes in X-ray binaries. MOXE will be sensitive to sources as faint as 2 milliCrab (56) in 1 day, and cover the 2-20 keV band.

A Gas Scintillation Counter (GSC) with high background rejection capability, fast timing char-acteristics and good energy resolution has been developed for quasimolecular X-ray spectroscopy in inelastic heavy ion - atom collisions. The detector presented in this paper consists of a high pressure Xe-filled absorption cell and a secondary scintillation parallel gap. Highly efficient de-tection of the primary light provides a time resolution of 3 ns (FWHM). The energy resolution is 4.3% (FWHM) for 60 keV X-rays. A rejection efficiency of 92% for Compton background in the energy range between 35 and 160 keV is obtained by applying the K - fluorescence gating method and pulse-shape analysis, to the secondary scintillation pulse.

Although multiwire detectors have been overtaken in some applications of x-ray imaging, they have certain characteristics which can be used to advantage in synchrotron radiation studies, for example in small angle diffraction or scattering experiments on biological systems.In particular,the size of the active region of the detector and the total number of pixels can be conveniently matched to the dimensions of the synchrotron beam and to the optics of the beam line camera.Furthermore,the large dynamic range inherent in single photon counting systems can be exploited to ensure the collection of high quality data even when the diffuse and coherent scattering factor varies over several orders of magnitude. Linear and two dimensional detectors are in regular use at the Daresbury Synchrotron Radiation Source all using the delay line readout method and a standardised data acquisition system which includes facilities for time resolved measurements. The source characteristics and the beam line optical instrumentation are described to show the properties which influence the design of imaging detectors and from this the parameters of the detectors currently in use are examined together with details of test measurements. Some examples of experimental results are given. The development of systems for one and two dimensional detectors to replace the delay line readout method and to operate at the very high count rates available from synchrotron sources is being actively pursued and will soon reach prototype stage.The design of these systems which use custom designed circuits and high speed digital correlation techniques will be outlined.

The GSI 5m grazing incidence spectrometer has been prepared and tested off-line using a Penning discharge light source. We have developed a two-dimensional position-sensitive detector as well as hardware and software for data accumulation, display and analysis. This detector is in situ interchangeable with a double scannner. First measurements have been made of recoil and beam foil spectra of highly ionized atoms using 1.4 MeV/u ion beams from the UNILAC-accelerator at GSI (Gesellschaft far Schwerionenforschung mbH, Darmstadt). The current status of the instrument, the position-sensitive detector system and examples of measured spectra are presented.

We have applied the technique of Doppler tuned spectroscopy, developed by Schmeider and Marrusl , to high Z, highly ionized atomic systems. Our Doppler spectrometer is tuned to the ~102 keV Lyman-alpha radiation in hydrogen-like uranium. This paper reviews this instrument. The systematic and random errors that are important for spectrometer accuracy are explained. Advantages of the Doppler technique in the high Z regime over crystal spectrometers are discussed. Preliminary results from a successful run at the Lawrence Berkeley Laboratory (LBL) BEVALAC are presented.

Two types of wireless position sensitive X-ray proportional counters are under development at the Danish Space Research Institute. One detector - the microstrip proportional counter - employs very narrowly spaced conducting strips deposited on an isolating substrate instead of wires. The gas gain is uniform over the entire detector area and the achievable energy resolution is close to or better than the best achievable for single wire proportional counters. The position readout is made using a wedge and strip electrode mounted on the back-side of the insulating glass substrate. The second detector employs a uniform electric field between two parallel electrodes in order to achieve amplification. Parallel electrodes have better energy resolution, better timing resolution and are easier to construct and more durable than multiwire chambers. The parallel gap is formed between an etched Ni mesh and a segmented anode in the form of a wedge and strip electrode. The X-ray photon energy is derived from the mesh electrode, whereas the position information is taken from the anode. Submilimeter position resolutions have been achieved. In both detectors the energy signal has a very fast risetime and background rejection based on pulse shape analysis is, therefore, very efficient. The background rejection efficiencies achieved and the optimum rejection method for spaceborne detectors will be discussed.

A new generation of proportional counter is currently being developed at MSFC. The device, known as a multistep fluorescence gated detector, combines superior energy and spatial resolution with a very high degree of background rejection to produce a versatile instrument ideally suited to x-ray astronomy in the 20-100 keV energy range.

We describe the gas proportional counter used for X-ray detection on the Solar-A Bragg Crystal Spectrometer Instrument. The sealed detector utilises a multi-anode geometry together with a wedge and wedge (or backgam-mon) cathode pattern to provide one-dimensional imaging along the dispersion axis. We discuss the development programme which has lead up the design of the Prototype Detector. Finally, we present results of the imaging performance, energy resolution and countrate capability.

The ROSAT position sensitive proportional counter is a multi wire X-ray detector which uses a mixture of Argon, Xenon and Methan as counter gas. In the X-ray energy band from 0.1 keV to 2.2 keV, this gas shows several absorption edges, caused by Argon-L and Xenon-N shells between 100 eV and 350 eV, and Xenon-M shells between 670 eV and 1150 eV. To measure the anode pulse height as a function of X-ray energy, we set up an X-ray spectrometer, using a transmission grating with 1000 lines per mm and a high intensity X-ray continuum source. The spectrometer had a resolution of 0.3 A. Besides the well known discontinuity of the pulse height at the Argon-L III/II edges, we could identify almost all Xenon edges in our energy range. Between the edges, the anode pulse height is proportional to the X-ray energy. At the edges, the pulse height drops, corresponding to an energy loss of a few electron volt. We will describe the measurements and present the results.

A collaboration of astrophysicists from Iowa State University, University of Michigan, the Smithsonian Astro-physical Observatory, England, and Ireland plan to construct a new 10-meter diameter γ-ray Cerenkov telescope on Mt. Hopkins in Arizona. By operating in coincidence with the original 10-meter reflector, the sensitivity for 7-ray detection will improve by more than an order of magnitude. This increase will permit observation of compact objects with the intrinsic luminosity of the Crab nebula which lie within a range of 7 kiloparsecs. The new telescope, named GRANITE (for Gamma-Ray Astrophysics New Imaging Telescope), will include a 109 element imaging photon detector with a 0.2° pixel size. The entire system consists of a steerable alti-azimuth mount, a faceted mirror assembly, a highly segmented photon detector, and ancilliary data acquisition and control electronics. The reflector mount will be fabricated using techniques developed for satellite communications dishes. The mirrors will be second-surface aluminized borosilicate glass optimized for wavelengths in the range of 300 to 400 nanometers. Signals from the photomultiplier detector array will be characterized and recorded according to their amplitude, time of arrival, and width. Each of these subsystems will be described with an emphasis on the trade-offs between cost and instrument performance. This telescope is considered an engineering prototype for a large array of aerenkov detectors which will further enhance our ability to detect astrophysical sources of very high energy gamma rays.

We report a novel, imaging, low-energy (.1 - 10 MeV) gamma-ray spectrometer. This device has excellent position resolution ( ~2 mm @ 350 keV), near unity quantum efficiency, and alkali halide-type energy resolution at an extremely low cost per unit area. This is possible through the separation of the energy and position sensing functions in an alkali halide-based gamma-ray detector.

We report on the development of a pulse shape discrimination (PSD) technique to reject the B-decay background resulting from activation of germanium (Ge) gamma-ray detectors by cosmic ray secondaries. These B-decays are a major source of background at 0.2-2 MeV energies in well shielded Ge detector systems. The technique exploits the difference between the detected current pulse shapes of single- and multiple-site energy depositions within the detector: B-decays are primarily single-site events while photons at these energies typically Compton scatter before being photoelectrically absorbed to produce multiple-site events. Algorithms have been developed to distinguish between single- and multiple-site pulse shapes. Depending upon the amount of background due to sources other than B-decay, PSD can more than double the detector sensitivity. In addition, we report on tests of PSD by laboratory activation of a detector with a fast neutron source, and on the first direct measurement of the B-decay background at balloon float altitude using a Ge detector with PSD.

We discuss the application of a high resolution liquid xenon imaging chamber as a γ-ray telescope for medium energy astrophysics. The chamber, operated in the Time Projection Mode, will be capable to image any ionizing event occurring within its sensitive volume. Gamma-ray events with multiple Compton interactions will be identified as such, thus significantly enhancing the detection efficiency over a wide energy range. This represents the main advantage of the proposed liquid xenon instrument over more conventional double scatter Compton telescopes, in which stringent topological constraints limit considerably the acceptance. In the Compton regime, the excellent energy and position resolution of the detector, on the order of 3% FWHM at 1 MeV and of 250 pm RMS, respectively, will result in a 1a angular resolution of 0.5° - 0.3° for 7-ray energies of 1-20 MeV. The ambiguity in source location that characterizes the Compton measurement can be removed for 7-ray events of high enough energy to allow the reconstruction of the direction of the Compton electron. In the pair production regime, the incoming γ-ray direction can also be uniquely determined from the reconstructed openining angle of the electron-positron pair. An effective discrimination against charged and neutral background events is a direct consequence of the detector imaging capability. The versatility of the liquid xenon telescope and its unique characteristics will allow a large variety of γ-ray emitting sources to be explored with high sensitivity.

We present a concept for a balloon-borne imaging hybrid proportional counter/phoswich detector of medium to hard X-rays. The phoswich would be optically coupled to the exit window of the proportional counter, and both detectors would use a common position-sensitive readout. We anticipate that such a detector could combine the good energy and position resolution and excellent background rejection ability of the proportional counter for incident photon energies <100 keV with the extended response of the phoswich for higher energies. The phoswich could also be used to reject Compton scattering events in the proportional counter. We are studying this detector concept using numerical simulations of a 400 cm² square prototype detector. We use a Monte Carlo approach, properly accounting for range, penetration depth, and diffusion effects in the proportional counter. We explicitly model the propagation of the scintillation light from the proportional counter through a waveshifter and the phoswich, and its detection with an Anger camera arrangement of Hamamatsu crossed-wire anode photomultiplier tubes. Results from this simulation indicate that current levels of proportional counter and phoswich performance are attainable at small cost in quantum efficiency, compared to a bare phoswich detector. We also report some rough calculations of the background rejection efficiency in the xenon and the phoswich.

To image X-radiation efficiently at energies above about 10 keV requires the use of "shadow optics" techniques. The Pinhole/Occulter Facility (P/OF) represents an application of these techniques for observations in high-energy astrophysics, especially the study of solar coronal activity in hard X-rays and γ-rays. P/OF will achieve angular resolutions on the order of 0.2 arc s for an instrument deployment length of 50 m. Because of this large structural scale, P/OF has been proposed as an attached payload for the Space Station. In the meanwhile, several smaller-scale instruments are being developed.

A high angular resolution, wide field camera system (WFCS) operating in the 30 to 100 keV band has been proposed for NASA's gamma ray astronomy program. It is intended for long duration balloon flights initially and for deployment in space, eventually. The instrument contains two orthogonal units consisting of a multiple slit collimator and a two-dimensional position sensitive detector. Each unit provides a one-dimensional position. Gamma ray bursts and soft gamma repeaters will be imaged and positioned to a few square arcminutes or better. There will be a net effective area of 500 cm2 (60 keV) and an energy resolution of 4% for spectroscopy of possible cyclotron features. During a two-week balloon flight from Antarctica, the WFCS will simultaneously monitor intensity variations of all hard x-ray sources above the level of 25 milicrabs within its r ster field of view and improve the positions of unidentified objects. When it is deployed in space above the atmosphere attenuation, the WFCS will have five times more sensitivity, a larger band width, and a larger field of view. It will be able to position over one hundred bursts per year. A fine positioning feature can be added to the system by winding wires around the detector and collimator. This embeds an imaging modulation collimator that operates in the 15 to 50 keV band. Simulations suggest that several gamma rays bursts per year could be located with statistical errors as small as 10-2 (arcmin)2.

We are constructing a balloon experiment, GRATIS, which will perform the first arcminute imaging of cosmic sources in the 30 - 200 keV energy band. Observations conducted with GRATIS can provide data relevant to several key problems in high energy astrophysics including the physical processes responsible for the high energy tail observed in the soft gamma-ray spectra of clusters of galaxies and the origin of both the diffuse and point source components of the gamma-ray emission from the Galactic Center. This paper discusses the scientific motivations in more detail, outlines the experiment, discusses several aspects of the design and construction of hardware components, gives an overview of the stabilized platform, and shows the expected performance and sensitivity.

In order to satisfy the increasing interest in the large format scientific grade CCD with high resolution capability, a full frame 1024 x 1024 four phase CCD has been designed, fabricated and tested. The devices show a 5 electrons noise at - 100°C and very good transfer efficiency. A four quadrant organization with four video outputs allows a 20 ms minimum readout time. Performances at room temperature and low temperature will be presented. Plan for future enhancements -back side illumination and high resistivity silicon substrate- will be discussed.

Multi-phase CCDs have traditionally exhibited very poor sensitivity in the UV, EUV and soft x-ray due to the absorbing polysilicon layers associated with the technology. To bypass the problem, CCD manufacturers have been forced to either thin and back illuminate the sensor or deposit UV sensitive organic phosphor coatings. Virtual-phase technology however has resolved the frontside QE dilemma by leaving half of the pixel "open" by employing a "virtual electrode" allowing photons to enter into the photosensitive bulk silicon unimpeded. Unfortunately, unlike multi-phase CCDs, virtual-phase detectors typically have limited usage in low signal-level applications because of CTE and readout noise impediments. To circumvent these problem areas, a novel CCD technology referred to as open pinned-phase (OPP) was invented, the subject of this paper. Discussion includes design and process features of an OPP-CCD that are focused to unite multi- and virtual phase technologies. The new CCD promises to deliver high frontside sensitivity in conjunction with ultra-low signal level performance.

Amongst the space-borne X-ray astronomy observatories to be launched during the 1990's, two missions being studied within Europe are the JET-X instrument on the Soviet SPECTR R-G satellite, and the EPIC focal plane camera selected for ESA's XMM. The Leicester University X-ray Astronomy Group is developing focal plane detectors utilising EEV CCDs for both of these instruments. The key design requirements for these missions are discussed, and the expected performance of the CCDs is described.

We present the results of the extreme ultraviolet (EUV) flat field calibrations of two of the flight detectors to be flown on the Extreme Ultraviolet Explorer Satellite (EUVE). Images of ~40 million detected events binned 512 by 512 are sufficient to show MCP fixed pattern noise such as hexagonal microchannel multifiber bundle interfaces, "dead" spots, edge distortion, and differential nonlinearity. Differences due to photocathode material and dependencies on EUV wavelength are also described. Over large spatial scales the detector response is flat to better than 10% of the mean response but at spatial scales less than 1 mm the variations from the mean can be as large as 20%.

We present the results of the transmission calibrations of the seven sets of flight integration filters for the Extreme Ultraviolet Explorer satellite. Absolute transmissions have been determined over six orders of magnitude at 28 wavelengths using the Berkeley EUV Calibration Facility. Models for the filter transmission over the extreme ultraviolet wavelength range have been derived from these results and from calibrations of other test filters. Witness test filters composed of foils identical to the flight integration filters have also been calibrated as part of a lifetesting program. This program is designed to monitor changes in the transmission and mechanical properties of the EUVE filters over the life-time of the mission (assembly, launch and operation). Recent results from the lifetest filter calibrations are also presented, representing data accumulated over a four year period.

The Berkeley Extreme-ultraviolet Airglow Rocket Spectrometer (BEARS), a multi-instrument sounding rocket pay-load, made comprehensive measurements of the Earth's dayglow. The primary instruments consisted of two near normal Rowland mount spectrometers: one channel to measure several atomic oxygen features at high spectral resolution (~ 1.5 Å) in the band passes of 980 - 1040 and 1300 - 1360 ⇔ and the other to measure EUV dayglow and the solar EUV simultaneously in a much broader bandpass (250 - 1150 Å) at moderate resolution (~10 Å). The payload also included a hydrogen Lyman a photometer to monitor the solar irradiance and geocoronal emissions. The instrument was calibrated at the EUV calibration facility at the University of California at Berkeley, and was subsequently launched successfully on September 30, 1988 aboard a four stage experimental sounding rocket, Black Brant XII flight 12.041 WT. The calibration procedure and resulting data is presented.

Conventional X-ray microcalorimeters have so far used ion-implanted resistors for thermometers. Recently, however, several new methods for sensing small temperature changes have been suggested that are non-dissipative. Such devices may have intrinsically better energy resolution by eliminating the Johnson noise present in resistive devices. We are investigating the use of kinetic inductance thermometers for X-ray microcalorimeters. This technique exploits the strong temperature dependence of magnetic penetration depth of thin superconducting films. Our prototype system, designed for operation at 1.5 K, uses films of aluminum and tin. Once the expected temperature sensitivity and alpha particle detection have been demonstrated, we expect to replace the aluminum with titanium or another material with a suitable critical temperature and operate the device at 0.3 K. At this temperature the energy resolution from thermal noise should be sufficiently good to allow X-ray detection.

We are developing cryogenically-cooled microcalorimeters for high resolution x-ray spectroscopy. Using neutron transmutation-doped (NTD) germanium thermistors as the x-ray absorber, we have achieved an energy resolution of 70 eV at a temperature of 0.3 K. There is strong evidence for incomplete conversion of x-ray energy into thermal energy when the photon is absorbed in the bulk of the NTD germanium. We believe that the nonthermal energy component manifests as ionization, none of which is converted to thermal energy within the measurement time of the system. As in an ionization detector, the division between ionization and thermal energy is statistically uncertain and leads to a lower limit to the energy resolution measured using either the thermal or ionization signal. Complete conversion to thermal energy with no loss to ionization appears to occur when the x-ray is absorbed by the metallic contacts. This will be discussed in the context of our most recent 0.3 K experiments.

The limiting performance of a niobium based super conducting tunnelling junction are examined. The application of such devices as wide band high resolution X-ray spectrometers for use in high energy astrophysics is discussed. At 6 keV the energy resolution of an initial development device was 130 eV (FWHM) operated at 1.6 K. Means of improving this preliminary experimental resolution are outlined.

We describe a sounding rocket experiment to investigate mechanisms governing the interactions between two of the fundamental components of the solar-terrestrial system: the solar ionizing radiation and the Earth's upper atmosphere. The experiment was designed to characterize the Extreme Ultraviolet (EUV) emissions resulting from these interactions in terms of physical parameters so that EUV remote sensing can be gainfully employed as a quantitative diagnostic of the terrestrial atmosphere and plasma environment. Although several EUV observations of the Earth's airglow have been made, these measurements have never been complemented with simultaneous measurements of the solar EUV flux, thereby making the interpretations somewhat ambiguous. The payload consisted of (1) a high resolution (-1.5 Å) spectrometer to measure the EUV emissions (980-1360 A) of the Earth's dayglow, (2) a moderate resolution (-10 Å) EUV spectrometer (250-1450 Å), to measure the solar irradiation responsible for the photoelectron production, and (3) a hydrogen Lyman Alpha photometer to monitor the solar irradiance and geocoronal emissions. The experiment was con-ducted from a four-stage Black Brant XII sounding rocket launched from NASA Wallops Flight Facility in Wallops Island, Virginia, on September 30, 1988.

The High Resolution Camera (HRC) is one of four instruments selected to fly on the NASA Advanced X-Ray Astrophysics Facility (AXAF) [1]. The HRC is designed to detect single X-ray photon events in the soft X-ray energy range from 0.1 to 10. KeV. The measured spatial resolution (FWHM) is 25 pm over a 100 cm² detecting area. This paper investigates the accuracy and limitations of the position algorithm used with the coarse/fine resistive wire readout system.

We report investigations of delay line configurations used to encode photon event locations in microchannel plate (MCP) detectors. Several delay line schemes of planar and multilayer structure are discussed. We examine the importance of the delay line substrate material, and show that the raw signals from delay lines are narrow (~3-4ns FWHM). The factors determining the delay line resolution are evaluated, and we demonstrate that these are in agreement with measurements. Resolutions of -18gm FWHM have been achieved. Measurements of the linearity of the delay line readout show that event centroid locations deviate from perfect linearity by less than 5011m, even with the very simple anode fabrication methods employed. The image stability has also been evaluated and we show that image shifts are less than one resolution element over a period of two months.

The current status in the development of an imaging low energy gas scintillation proportional counter is described. The detector is sensitive over the range 0.15-10 keV and in order to achieve the low energy response a driftless configuration with a thin plastic window has been adopted. The detector has been found to be a useful tool in the study of various physical process related to gas scintillation such as drift velocity, longitudinal diffusion, light production and the Fano factor for Xe. Results in all of these areas are also presented. Many of these results have been obtained through the use of high speed pulse digitization techniques.

The Reflection Grating Spectrometer experiment (RGS) on the X-ray Multi-Mirror Mission spacecraft (XMM) of the European Space Agency (ESA) consists of two identical instruments behind two of the three high throughput X-ray telescopes. The instruments will achieve high energy resolution and high efficiency in the combined first and second order of diffraction in the wavelength range between 5 and 35 Å. The design incorporates an array of reflection gratings placed n the converging beam at the exit from the X-ray telescope. The grating stack picks off roughly half of the X-ray light and diffracts it to the array of charge-coupled device (CCD) detectors offset from the telescope focal plane. The remaining light passes undeflected through the grating stack where it can be utilised by instruments located in the focal plane. Both the gratings and the detector are placed on the Rowland circle. The reflection gratings diffract first, second and third order at high to moderate efficiency. The separation of the spectral orders is accomplished using the energy resolution of the CCD detectors. A set of ten CCD-chips (nine for spectroscopy, one for wavelength calibration) are arranged in a strip oriented tangentially to the Rowland circle. Since the optical design is nearly stigmatic, the spectrum of an on-axis point source will appear as a line image along the detector array. In order to reduce noise and dark current an operational temperature of -80°C is adopted for the CCD's. The cooling is provided through a passive radiator. The chips are read out sequentially with a common electronics chain. Each chip is configured in an "image and store" mode in which the image is first acquired over half the chip and transferred to the other half for storage prior to read out.

ASTRO-D is the next X-ray mission in Japan. The main instrument of ASTRO-D is 4 sets of thin foil conical mirrors with focal plane detectors of CCDs and Imaging Gas Scintillation Proportional Counters (IGSPC). The total effective area of the 4 mirrors is about 500 cm2 at 6 - 7 keV, with energy resolutions about 2% (FWHM) and 8% (FWHM) at 6 keV for CCD and IGSPC, respectively. The spatial resolution of the mirror is 2-3 arcmin in half power diameter, having a field of view of about 30 arcmin diameter. ASTRO-D will provide us with a unique and powerful capability to study high energy astrophysics in the early 1990s.

The High Pressure Gas Scintillation Proportional Counter (HPGSPC), one of the experiments on board of the Italian-Dutch X-Ray Astronomy Satellite SAX, is a large area (450 cm2), xenon filled (5 atm.), high energy resolution (3% at 60 keV) detector sensitive in the energy range from 4 to 120 keV. In the paper we give a general description of the characteristic of the experiment. Some effort is dedicated to illustrate the on board energy correction algorithm required for preserving the potentially good full area energy resolution .

We describe a preliminary laboratory study of a prototype mosaic wedge-and-strip anode, a new class of readout system that will furnish large format, high resolution microchannel plate detectors with comparatively simple readout electronics. The goals of this study were to demonstrate the linearity of the mosaic anode algorithm, and to verify the predicted resolution performance in a realistic detector configuration. We find that the nonlinearity introduced at the boundary between two anodes is limited to 50-100 pm. We also show that the spatial resolution of the detector is limited mainly by partition noise to ~ 35 μm (FWHM) at a gain of 2 x 107. We have also begun a systematic investigation of the charge distribution arriving at the anode. Using the relative charges arriving on the two anodes of our mosaic pattern, we have determined the detailed shape of the distribution and its dependence on MCP-anode voltage, MCP voltage, and pulse height. We find a significant dependence of the profile on pulse height, which can introduce a pulse height dependence to the centroid calculation, particularly near the anode edges. We discuss improved anode designs which will achieve the optimal performance.

The technique of obtaining quantitative data from high resolution soft X-ray photographic images produced by grazing incidence optics was successfully developed to a high degree during the AS&E Solar Research Sounding Rocket Program and the S-054 X-Ray Spectrographic Telescope Experiment Program on Skylab. Continued use of soft X-ray photographic imaging in sounding rocket flights of the AS&E High Resolution Solar Soft X-Ray Imaging Payload has provided opportunities to further develop these techniques. The developments discussed include: (1) The calibration and use of an inexpensive, commercially available microprocessor controlled drum type film processor for photometric film development. (2) The use of Kodak Techni-cal Pan 2415 film and Kodak SO-253 High Speed Holographic film for improved resolu-tion. (3) The application of a technique described by Cook, Ewing, and Sutton(1) for determining the film characteristics curves from density histograms of the flight film. Although the superior sensitivity, noise level, and linearity of microchannel plate and CCD detectors attracts the development efforts of many groups working in soft X-ray imaging, the high spatial resolution and dynamic range as well as the reliability and ease of application of photographic media assures the continued use of these techniques in solar X-ray astronomy observations.

Imaging detectors utilising microchannel plates with electronic position readouts, in general, require the output charge cloud to have a well defined size and form. We describe an experimental technique to measure this spatial distribution. We present measurements of the distribution under a wide variety of operating regimes and discuss the importance of each of the detector operating parameters. We show that the radial charge distribution has a general form which can be described by the sum of two exponentials.

A front-illuminated virtual phase CCD with a 1024 x 1024 pixel array manufactured by Texas Instruments has been calibrated with x-rays in the 5.4 Å to 67.7 Å range. These calibrations are a part of the Solar-Å investigation, a joint Japanese-US-UK space project to be launched in August 1991. The absolute quantum efficiency (QE) of the CCD has been measured and is adequately understood in terms of a model involving the known architecture of the CCD at all wavelengths except 44.7 Å and 67.7 Å, where higher than expected QE values are obtained. Flat field images have been obtained at 8.3 Å (Al-K) and 44.7 Å (C-K) and have been compared with visible light images of the Sun. The Al-K images appear relatively featureless but those in C-K and visible light exhibit common features that are related to artifacts in the CCD. The higher than expected QE results at soft x-ray and EUV wavelengths may be caused by fluorescence occurring in the absorbing layers on the CCD entrance aperture. If this interpretation is correct, it may be necessary to conduct future calibrations of CCDs more carefully at soft x-ray and extreme ultraviolet wavelengths, particularly if some of the fluorescence occurs in molecular contaminants on its entrance aperture.

The second fabrication of fully depletable, backside illuminatable pn CCD's on high resistivity 280p,m thick silicon (σ = 2.5 kΩcm) has been tested. Two dimensional X-ray imaging was performed; the multilinear arrangement of the pixel-rows (pixel size 100 x 54μm2) allows a fast readout of the entire detector. We present results of measurements concerning the static device characteristics (leakage currents) and their temperature dependance. Their contributions to the detector noise are calculated. Entrance window thicknesses for this kind of devices have been measured in two different ways. Quantum detection efficiencies in the energy range from 100eV to 10keV are derived and compared to first results obtained with synchrotron radiation in the spectral range between 500eV and 1900eV. An improved design using epitactical silicon with a more suitable geometry and an on-chip JFET electronics has been developed and is currently being fabricated. Further developed devices of this kind are proposed as focal plane instruments for one EPIC (European X-ray Photon Imaging Counter) on the XMM (X-ray Multi Mirror) mission.

Detectors for x-ray (1-10 keV) astronomy based on silicon drift chamber (SDC) devices offer significant advantages over some types of existing detector and the potential performance of such devices is summarised. Our development program is outlined together with a discussion of device designs which are being pursued. Results are presented from some recently acquired two-dimensional drift devices working at room temperature, and from some large area drift diodes working at low temperature.

A polarimeter utilizing the polarization dependence of x-ray scattering from the low Z metal Lithium will be flown on the SPECTRUM-X-Gamma missionl. The instrument will reside at the focus of one of the SODART x-ray telescopes. An important design consideration is the spurious polarization signature which occurs when unpolarized incident flux is focused a relatively small distance away from the precise axis of symmetry. In this paper we present the results of analytical and Monte-Carlo studies of this effect.

Future high-throughput X-ray astronomy missions require the development of very thin and light-weight components. These demands can be meet by the use of replica technology which allows great numbers of thin mirrors to be easily produced. We present first results obtained with the use of galvanoplastic technology for the pruduction of ultrathin (below 1 mm wall thickness) components for the use in future imaging X-ray. experiments. Ultrathin mirrors of different geometries (flat, conical and Wolter 1) were produced this way and its properties are discussed. Results of first tests indicate the galvanoplastic technology is promising in the development and manufactory of high-throughput X-ray optics components. Advantages and drawbacks of this technology are shown and discussed by comparison with other techniques.

XMM is a highly nested (58 individual shells) Wolter-I type X-ray telescope with a focal length of 7.5 m consisting of 3 individual modules. The specified resolution (HEW) is 30 (goal 15) arcsec. In order to qualify single mirror shells and align and assemble the whole mirror module in a reasonable time it is inevitable to apply fast test and strongly converging alignment procedures. By means of two scanning laser beams intra- and extrafocal images of two mirror shells will be registered on a CCD-camera coupled to an image processing PC. One of the mirrors is already glued and serves as a reference while the second one has to be aligned yet. From the data axial and lateral focus positions as well as focus dimensions are calculated. A feed back loop then shall activate a set of actuators coupled to the mirror to be aligned. In an iterative way the alignment status of this mirror will be optimized. Finally, this mirror is cemented under optical control. First results from a basic test setup with only one mirror will be presented. The work is performed under ESA contract for XMM.

The field of multilayer optics for the X-ray, Soft X-ray and extreme ultra violet is maturing at a rapid pace. There are more than fourty groups worldwide actively working in this area. A large part of these efforts are directed to improving the quality of multilayer structures by developing a better understanding of the synthesis-structure-property relationships. Although the quality of multilayer structures may be substantially improved there are now significant instruemental apllications for these reflecting optics. In this paper the current status of this field is discussed.

An imaging-based technique has been modeled for its suitability and performance in measuring the spatial distribution of the absolute soft x-ray characterization of flat multilayer mirrors. Such a technique, if implemented experimentally, is anticipated to have substantially higher throughput ( wafers/day ) than is possible from prevailing non-imaging means.

Thin film deposition techniques currently being used to produce multilayer x-ray optics (MXOs) have difficulty producing smooth, uniform multilayers with d-spacings less than about twelve angstroms. We are investigating atomic layer epitaxy (ALE) as an alternative to these techniques. ALE is a relatively new thin film deposition technique which we believe can produce MXOs with very small d-spacings. ALE accomplishes this by depositing a single layer of atoms during each cycle of the deposition process. Multilayers deposited by ALE should have sharp interfaces and smooth, uniform layers with precise d-spacings.