We report on our ongoing work using Nb/Al/AIOx!Nb junctions for the detection ofx-rays. Detectors based on superconducting tunneling junctions offer the prospect of resolution over an order of magnitude higher than is obtainable with the current generation of semiconductor-based detectors. Unlike Sn junctions, these Nb-based devices are not degraded by repeated thermal cycling and are known to be exceptionally "radiation hard". We present results on measurements taken at 1.85 K, a temperature achievable with current space flight technology. These measurements include the current-voltage (1-V) curve, subgap current vs. temperature, the dependence of the superconducting current on the applied magnetic field (Fraunhofer pattern), x-ray pulses, and the spectra from a 6 keV x-ray source which gave an intrinsic device resolution of approximately 700 eV. A comparison of the x-ray spectrum peak with a known injected pulse of 105 electrons indicates the collection of more than 105electrons per 6 keV photon.

While much progress has been made towards improved energy reso1utvn in superconducting tunnel junction (STJ) detectors recently, results are still more than an order of magnitude worse than the theoretical limit. Several factors have been identified as contributing to degradation of energy resolution in STJ devices: recombination losses, parasitic quasiparticle trapping and quasiparticle diffusion into current leads. In addition, STJ detectors tend to have poor photon capture efficiency. Semiconducting detectors achieve their near theoretical energy resolutions and high efficiencies via doping and/or applying an external field to a pure substance. These methods are ineffective for STJ detectors, therefore such alternatives as engineered materials, consisting of multiple materials artificially patterned on the microscopic level, should be considered. The most common engineered structures in use are quasiparticle trapping configurations, which alleviate lead diffusion and detection efficiency problems. We have previously proposed a multilayered approach which addresses parasitic trapping, along with diffusion and efficiency. We now propose the possibility of an engineered structure which will alleviate quasiparticle recombination losses via the existence of a phononic band gap that overlaps the 2i energy of phonons produced during recombination of quasiparticles. We will present a 1D Kronig-Penny model for phonons normally incident to the layers of a multilayered superconducting tunnel junction as an idealized example

Superconductive tunneljunctions are under development as detectors for X-ray astronomy in the 0.5-10 keV energy range, because of their potentially high energy resolution (E < 10 eV) in combination with high detection efficiency. Especially absorber-junction combinations offer the prospect of high energy resolution detectors with a high detection efficiency and a reasonable ( 1 cm2) size. The proximity effect between the Nb absorber and the Al trapping layer plays a dominant role. A study of the proximity effect in Nb/Al/Al2 03/Al/Nb junctions with different Al-layer, the trapping layer, thicknesses is presented

High resolution X-ray spectroscopy provides a powerful tool for the diagnosis of plasmas and extra terrestrial X-ray sources. We are developing detectors based on superconducting tunnel junctions which will provide position sensitive detectors with much better energy resolution than current state of the art CCD cameras. The amount of energy required to create a charge carrier in a superconductor is about three orders of magnitude smaller than in standard semiconductor detectors. Consequently, the energy resolution, especially in the energy range below a few keV, is significantly enhanced. The drawback of the necessarily small size of superconducting tunnel junctions has been compensated by a separation of X-ray absorber and detecting tunnel junction ('quasiparticle trapping'). We report on results with our detector which can resolve the 5.89 keV manganese line with an energy resolution of better than 60 eV. In addition position resolution better than 5 um has been demonstrated with an absorber 470 jim long. To match the detector to the spot size of the X-ray optics in use, a multi element detector is under development.

We describe a new instrumental technique for interference spectroscopy, Spatial Heterodyne Spectroscopy (SHS), which promises to extend into the far-ultraviolet (FIJV; 1200 A - 2000 A) spectral region the large throughput advantage at high spectral resolution usually associated with Fabry-Perot and Michelson interferometers. In addition, SHS systems are compact in size, can be field widened to increase their throughp it advantage even further, and have no moving parts. SHS appears to be well suited for high resolution, space-based spectroscopy of faint interstellar emission lines in the far-ultraviolet. This has significant implications for the study of the dynamics and distribution of hot gas within the Galactic disk and halo. SHS systems built and tested in the laboratory at visible and UV wavelengths have verified the basic concepts and performance characteristics of the technique. lit this paper we review the first proof-of-concept laboratory demonstrations of a field widened SHS configuration and a multiple order SHS system, which extends the spectral range of the basic device and present new results of sus performance in the vacuum ultraviolet (1850A). The design of an SHS system capable of obtaining velocity resolved spectra of the CIV )t155O doublet from the interstellar medium is also discussed.

The Diffuse X-Ray Spectrometer (DXS) experiment is scheduled to be flown as an attached Shuttle payload in December 1992. As of July 1992, it has completed pre-flight testing at Goddard Space Flight Center and being prepared for shipment to Kennedy Space Center for launch. DXS is designed to measure the spectrum of the low energy (0. 15 — 0.28 keY) diffuse x-ray background with — 10 eV energy resolution and 15° spatial resolution. During its 5-day Shuttle mission, DXS is to measure the spectrum of ten 15° x 15° regions lying along a single 150°-long great circle arc on the sky. DXS has two large area Bragg x-ray spectrometers to cover the wavelength range 44 —84 A using lead stearate Bragg crystals. The spectrometers are of a novel design and have a very large area—solid-angle product, so as to permit measurement of the wavelength spectrum of the cosmic low-energy diffuse x-ray background with good spectral resolution. The bulk of these x-rays are almost certainly from a very hot (T 106 K) component of the interstellar medium that occupies a large fraction of the interstellar volume near the Sun. Astrophysical plasmas near 1O K are rich in emission lines, and the relative strengths of these lines, besides providing information about the physical conditions of the emitting gas, also provide information about its composition, history and heating mechanisms. Each DXS detector consists of a curved panel of Bragg crystals mounted above a position-sensitive proportional counter. The spectrum is dispersed across the counter and all portions of the spectrum are measured at the same time. This eliminates the serious problem in conventional Bragg spectrometers of false spectral features being introduced by time-varying background. On the other hand, while all wavelengths are measured at the same time, the various wavelengths come from different directions in the sky. The spectrometers are therefore rocked back and forth about an axis perpendicular to the dispersed direction to obtain complete spectral coverage along an arc of the sky. This paper describes the DXS instrument concept and design and presents calculations of the anticipated data. It also provides a brief description of the DXS Shuttle payload and its operations

The Cosmic Unresolved X-ray Background InsLrumenl using CCDs (CUBIC ) is designed to obtain spectral observations of the Diffuse X-ray Background (DXRB) with moderate spectral resolution (E/E 10—60) over the energy range 0.2 — 10 keV using mechanically collimated CCDs. It will be launched on the NASA/Argentine minisat SA C-B in December 1994. At this time, it is the only planned satellite payload devoted to the study of the spectrum of the DXRB. Observations will consist of 1—2 day pointed exposures of each target direction, resulting in a series of high quality spectra. Over the anticipated 3 year lifetime of the satellite, CUBIC will be able to study up to 50% of the sky with 5° x 5° spatial resolution for the subkilovolt Galactic diffuse background, and with 1O x 1O spatial resolution for the extragalactic diffuse background above 2 keV. CUBIC will obtain high quality non-dispersive spectra of soft X-ray emission from the interstellar medium, supernova remnants, and some bright sources, and will make a sensitive search for line emission or other features in the extragalactic cosmic X-ray background from 2 — 10 keY

The Array of Low Energy X-ray Imaging Sensors (ALEXIS) experiment consists of a mini-satellite containing six wide angle EUV/ultrasoft X-ray telescopes. Its purpose is to mp out the sky in three narrow (5%) baridpasses around 66, 71, arid 93 eV. The mission will be launched on the Pegasus Air Launched Vehicle in 1992 into a 400 nautical mile, high inclination orbit. The project is a collaborative effort between Los Alamos National Laboratory, Sandia National Laboratory, and the University of California-Berkeley Space Sciences Laboratory. The six telescopes are arranged in three pairs in such a manner that as the satellite spins twice a minute they scan the entire antisolar hemisphere. Each f/i telescope consists of a spherical multilayer coated mirror with a spherical microchannel plate detector located at the prime focus and a thin aluminum or lexan/boron filter in front of the detector. The multilayer coatings determine the bandpasses of the telescopes. Each telescope has a field of view of 33 degrees. Unlike grazing incidence x-ray telescopes, the point spread function is uniform over the entire field of view with a FWHM of O.5degrees determined by spherical aberration. In this paper we present the status of the project as of July i992 as well as summary results from the pre-flight telescope calibration procedures.

Microstrip detectors are an exciting new development in proportional counter design in which the usual discrete anode and cathode wires are replaced by conducting strips on an insulating or partially insulating substrate. The devices are fabricated using integrated circuit-type photolithographic techniques and hence offer very high spatial accuracy and uniformity together with the capability of producing extremely fine electrode structures. First introduced by Oed, microstrip proportional counters have now been variously reported having 30 im spatial resolution, rate capacities to iO' mm2 s, and an energy resolution ofbetter than 11% FWHM at5.9 keV. They have been fabricated with anode bars down to 2 tm and on a variety of substrate materials including thin films which can be molded to different shapes. This review will examine the development ofthe microstrip detector with emphasis on the qualities which make this detector particularly interesting for use in astronomy.

Four imaging proportional counters are to be flown aboard the Russian mission Spectrum-XGamma as a part of the Stellar X-Ray Polanmeter. The gas mixture will be based on Xe-Ar. We have performed some Monte Carlo calculations to investigate the impact of gas mixture and material choices with respect to gamma and neutron induced background. We have used the latest version of MCNP code for the neutron and gamma transport.

The Stellar X-Ray Polarimeter employs the same Imaging Proportional Counters for both the Bragg and the scattering stage. We show the main characteristics of these detectors and their performances on the basis of tests on the Technical Constructive Model and on the Engineering Models.

Microstrip detectors are an exciting new development in proportional counter design in which the planes of discrete anode and cathode wires are replaced by conducting strips on an insulating or partially insulating substrate. The microstrips are fabricated using integrated circuit-type photolithography techniques and therefore offer very high spatial accuracy and uniformity. A development program is underway at Marshall Space Flight Center (MSFC) to produce large-area microstrips for use in an x-ray detector balloon flight program and to investigate the general performance limits of these new devices. Microstrips tested so far have been fabricated both in-house using standard photolithographic techniques and by an outside contractor using electron beam technology. Various substrate materials have been tested along with different electrode configurations. The distributions of pickup on subdivided cathodes on both top and bottom surfaces of the microstrips are also being investigated for use as two- dimensional imaging detectors. Data from these tests in the development of a large-area device will be presented.

The performance of an imaging gas scintillation proportional counter is described over the energy-range from 100 eV to 10 keV. The low energy response of the detector is achieved using a driftless configuration and a thin polyimide foil as X-ray entrance window. Measurements address the linearity of its response, its energy- and spatial-resolution by exposure to a collimated X-ray beam of diameter 50 micrometers .

The preliminary design for the 15 - 250 keV, 200 cm², phoswich detectors for the High Energy X-ray Timing Experiment (HEXTE) for NASA's X-ray Timing Explorer mission has been completed, and the first engineering model has been fabricated. This unit has undergone extensive environmental and performance testing, including extended vibration, thermal range, resolution, uniformity, and pulse shape, and is within specifications for all tests. Broad beam energy resolution of better than 15% at 60 keV and clear separation of NaI and CsI pulse shape peaks are seen. The design and test results will be presented.

A nuclear fission debris tracker, generally referred to as Package B, has been flown aboard Defense Meteorological Satellite Program (DMSP) satellites since 1976. More recently, this instrument has been redesigned in order to obtain additional functions. Since June 1987, four redesigned instruments have been flown. The first portion of this report presents a detailed description of the recent instruments and orbital parameters. The second half of the report concentrates on data representing periods of background and events of scientific interest.

The hard X-ray/soft gamma-ray telescope SIGMA has been successfully operating for more than two years aboard the soviet spacecraft GRANAT. This paper is intended to give a report of the most important technical as well as astrophysical inferences which have been obtained from this mission. From these, the mandatory capabilities of a future mission with their relative priorities can be drawn. The most important ones are (1) simultaneous spectral and imaging capabilities, (2) a wide field of view, and (3) a better sensitivity at 0.5 MeV. A sketch of a possible future satellite experiment fulfilling these requirements is given. It is a spectral imager in the sense that priority is given to the angular resolution in comparison with the spectral resolution. Its field of view (360 degree(s) X 10 degree(s)) enables continuous monitoring of the galactic plane emission, involving no cooling, no mechanics, and a coarse stabilization, it should be very reliable, thus allowing a long duration mission. A highly eccentric orbit of the same type as that of GRANAT would be the most efficient.

The Danish Space Research Institute will provide a set of four imaging microstrip proportional counters (MSPC) as part of XSPECT, the Danish contribution to the SODART telescopes. A high- and a low-energy detector (HEPC and LEPC) will be provided for each of the SODART telescopes. The design is fixed and a prototype of LEPC is under construction. The present paper describes the imaging properties of this detector. The inherent position resolution is < 0.2 mm around 6 keV, and positional nonlinearities are < 0.1 mm. The gas gain is independent of position to better than 0.5%. Finally, the point spread function, important for studying weak objects in the vicinity of strong ones, has been measured.

The major telescopes on board the SPECTRUM-X-GAMMA satellite are two SODART X-ray telescopes with 8 m focal lengths. One of them includes the Finnish experiment SIXA (Silicon X-ray Array detector) as one of its focal plane instruments. SIXA's main task will be the measurement of X-ray spectra with good resolution. The SIXA detector capsule consists of 19 discrete, circular, and closely packed lithium drifted silicon detector elements. A passive cooling system on the satellite provides 110 - 120 K operating temperature for the detector. Special attention has been paid to reducing detector leakage currents in order to achieve the desired resolution of 170 - 180 eV at 6 keV for 50 mm² active area detector elements within the temperature range of the cooler. In a parallel study, fabrication of 19 separate measuring pixels on a single lithium drifted silicon wafer is being investigated. The analog electronics section consists of 19 parallel amplifier channels. Two microprocessors are used to provide up to four simultaneous measurement modes for different scientific purposes. Use of hard disk drives in hermetically sealed containers as mass memory is under study. This paper gives an updated description of the SIXA spectrometer concept.

The Objective Crystal Spectrometer (OXS) on the SPECTRUM-X-GAMMA satellite will carry these types of natural crystals LiF(220), Ge(111) and RAP(001). They will be used to study, among others, the H- and the He-like emission from the cosmically important elements Fe, S, Ar and O. More than 300 LiF-crystals of dimension approximately 23 X 63 mm² are required to cover one side of a large (approximately 1000 X 600 mm²) panel which is to be mounted in front of one of the high throughput X-ray telescopes. A qualification study, performed at the Danish Space Research Institute (DSRI), examined a large sample of LiF(220) crystals at Cu-K(alpha) ₂ (8.0278 keV). Data from 124 flight crystals yields an average FWHM of rocking curves of 2.3 arcmin with a standard deviation of 0.4 arcmin. For more than 80% of the crystals, angular deviation of the (220) planes from the actual crystal surface is less than 1.5 arcmin. These data will be used to select the best crystals for the flight panel and will determine precisely the orientation of the crystals mounted on the OXS. Eight crystals were glued onto a small test panel of the OXS and for only one crystal was there measured a significant deviation of the crystal properties, including alignment relative to the others.

A prototype spectral filter was developed to be used as a radiation entrance window for a satellite borne CCD (Charge coupled device) X-ray imaging detector, which is presently under development within the EOBB (Electro-Optical-Breadboard) phase of ESA's XMM project. The unsupported filter has an effective size of 30 mm X 10 mm and is composed of multi-layered thin films of parylene N, aluminum, and carbon with mass densities of 25, 30 and 25 (mu) g/cm² respectively. CCD's have a broad spectral response ranging from the X-ray to the NIR (Near Infrared) range. For X-ray observations the filter being located in front of the detector must suppress the radiation of VIS (Visible) and UV (Ultraviolet) stars by more than 6 orders of magnitude and be highly transparent at energies above 0.1 keV. The technique to manufacture the windows and the measurements of the spectral transmittance as well as the environmental testing is described. The performance data are given.

The results of some measurements to characterize the performance of various cryogenically cooled CCDs and of a Multi Anode Microchannel Array detector in the Extreme UltraViolet region (EUV) are presented. A performance comparison between the two different types of detector was made: from these measurements some indications can be obtained which say in what conditions and for what applications one detector is preferable to the other. This can have some important implications, for example in choosing a detector for a space mission.

Large area CCD arrays, 770 X 1024 pixels, with 27 micrometers square pixels and packaged in matching pairs in a ruggedized focal plane assembly have been developed for the JET-X instrument for the Russian Spectrum-RG spacecraft. The devices achieve low noise readout (<EQ 5 electrons rms), low dark current (< 1 electron/pixel/frame-integration time) and high charge transfer efficiency (> 0.99997) enabling the device to combine high quantum efficiency and good energy resolution over the operating range of JET-X. New results from flight prototype JET-X CCD's will be presented which reveal the detail of charge spreading behavior in the device and the consequent effect on quantum efficiency, energy resolution and background rejection. Theoretical modelling and simulation of these processes are used to analyze the experimental results.

In this paper we describe the electro-optical characterization of three types of CCDs manufactured by the English Electric Valve (EEV). The sensitive area of these CCDs is treated in order to enhance the UV response; in particular one is 'coronene'-coated, thinned, back-illuminated, one is 'lumigen'-coated, front-illuminated, and one is 'ion-implanted' thinned, back-illuminated. A technical description of the CCDs and the adopted coating process is given. The CCD characteristics such as the read-out noise, the pixel non- uniformity, the dark current and the quantum efficiency in the 2000 - 10500 angstroms range, are compared. A cosmic-rays analysis for these CCDs is also given.

The results from the first flight of our proportional counter in an imaging telescope led us to rebuild the detector in anticipation of a Fall 1992 flight. We have used a Penning gas mixture (xenon + 1% isobutylene) and introduced a preamplification region to improve the energy resolution. We have rebuilt the pressure vessel making novel use of molybdenum as the housing material in order to reduce the residual instrument background, particularly in the fluorescence-gated mode for which the detector design has been optimized. We have also increased the sensitive gas depth from 9 cm to 14 cm to further increase the sensitivity to both fluorescent pairs and conventional singles. Our calibrations have shown that the overall energy resolution of the detector has been enhanced by a factor of 2, and we predict that the sensitivity at float will increase by a factor of 3 in the 50 - 70 keV energy band.

Several types of ultrathin entrance windows have been developed for applications in spaceborne X-ray instruments. Active area diameters up to 140 mm have been achieved. The latest windows developed have a transmission of > 20% at B K(alpha) and > 40% at N K(alpha) . A new gas block layer type utilizing aluminum nitride has been developed, as well as semitransparent support structures for the membranes. The effects of pressure-induced strain, radiation and atomic oxygen corrosion on the gas leak properties of the windows has been studied.

The light emitted by electron avalanches in a parallel plate chamber can be used to image the tracks of photoelectrons liberated by the interaction of an incident x-ray with the gas filling the chamber. The different morphologies of photoelectron tracks and minimum ionizing tracks can be used for charged particle rejection. The initial direction (before scattering) of the liberated photoelectron also contains information about the polarization of the incident radiation. We have built a small test chamber with which we have imaged photoelectron tracks using an intensified CCD camera. Our results show that optical imaging could be used in a hard x-ray imaging polarimeter useful for astronomy.

The influence of the secondary neutrons and photons, produced by cosmic ray interactions with the spacecraft, on the background of X-ray proportional counters used for astronomical observations from satellite, is investigated by means of two Monte Carlo codes. The GEANT3 code has been used to simulate the production and transport of particles and gamma rays in a structure that reproduces the masses and the materials of the satellite Spectrum-X-Gamma, to a relatively high degree of accuracy. Then, the MCNP code has been used to simulate the behavior of the multiwire proportional counters of SXRP, described in detail in a 3-D geometry, exposed to the neutron and gamma flux resulting from the interactions of the primary cosmic protons with the satellite. Preliminary results indicate that the photons produced as secondary particles in the structures of the satellite overwhelm by an order of magnitude those of the diffuse celestial background directly transmitted through the same structures, and that the estimated counting rate induced by the secondary neutrons and photons is comparable with that observed in similar space missions.

We have evaluated several square pore microchannel plates (MCP's) (25 mm MCP's with 85 micrometers diameter pores, 50:1 channel length to diameter (L/D) ratio, and 46 mm MCP's with 25 micrometers pores, 80:1 L/D ratio) from Philips. Measurements of the grain and pulse height distribution (PHD) vs voltage, PHD vs angle, background rate, flat field, quantum detection efficiency (QDE) vs angle, wavelength retarding field were made on these MCP's. The gain levels reach 2 - 3 X 10⁷, with PHD's of < 55%, and background rates of < 0.5 events cm^-2 sec^-1. Flat field measurements show the 25 micrometers square pore MCP's to have periodic modulation, but the 85 micrometers square pore MCP's to have no measurable modulation. The difference is thought to be due to the MCP stacking configurations. The QDE as a function of wavelength for the square pore MCP's is not markedly different from that of normal uncoated round pore MCP's. The only significant difference is that the QDE variation with angle is much more rapid for the 25 micrometers square pore MCP's. Microscope examination reveals that the pore alignment is quite good for the imaging quality square pore MCP's. Low radioactivity MCP's from Galileo with an 80:1 L/D ratio, 10 micrometers pores, and a 32 mm active area were also tested as a stacked back-back pair. Background events were uniformly distributed over the field of view with an average rate of 0.063 events cm^-2 sec^-1. Surrounding the detector chamber by lead shield blocks reduced the background rate to only 0.028 events cm^-2 sec^-1 which is only a factor of 2 to 3 higher than the expected cosmic ray rate.

It has been found that the gain depression in MCP's operated at high gains is a relatively long range phenomenon. Active pores can significantly depress the gain in the surrounding quiescent pores at distances of the order of millimeters. This is of fundamental importance for detectors in which high point source count rates are encountered. We have measured this effect for a variety of plate operating conditions and point source count rates and find that in all cases there is a constant limiting radius. We have also determined that the gain depression has a long term effect on the MCP.

The requirement for ever improved resolution at lower and lower photon levels has lead researchers to a number of various possible systems. Since we make image tubes on a custom basis, we have made several different photon counting tubes with different readout systems for a variety of laboratories. These readout systems are reviewed in our paper, and we attempt to analyze the state of the art with these different readout systems. Since all these systems use micro channel plate electron amplification, the fundamental properties of the channel plate effects them all to some degree. Advanced micro channel plates are being assessed, and the progress made is reviewed. Advanced electronic readout systems based upon the latest components, including transputers, promises increased resolution and count rates in systems optimized for X-ray and UV applications.

The SPAN position readout device uses a charge division and measurement method to encode the coordinates of the centroid of a charge cloud and thus provides a technique for imaging with photon counting detectors of various formats; for example, microchannel plate intensifiers and gas proportional counters. Its principle of operation causes the position resolution to substantially exceed the charge measurement precision. The reduced signal to noise requirement compared with the competitive devices of comparable imaging format size enables the SPAN readout system to operate at higher input count rates. We present imaging performance results from SPAN readout systems incorporated in several detector formats. The dependence of the physical parameters of the SPAN pattern design on the detector type and geometry together with the performance trade-offs between speed and resolution for these particular detectors are discussed. The practical implementation of the SPAN readout decoding algorithm is outlined. We describe the experimental applications for which the SPAN readout system has been proposed.

Microchannel plate (MCP) detectors are often used with charge division anode readouts, such as the SPAN anode, to provide high position resolution. This paper discusses the effect on image quality, of digitization (causing fixed patterning), electronic noise, pulse height distribution (PHD) and charge cloud size. The discussion is supported by experimental data obtained from a one dimensional SPAN anode, developed for the SOHO Coronal Diagnostic Spectrometer (CDS) Grazing Incidence Spectrometer (GIS). Results from a computer model of this detector, and from a charge cloud simulation model, are also included. The SPAN anode normally has three sinusoidal electrodes with phase differences of 120 degree(s)C. An alternative configuration is to use a phase difference of 90 degree(s)C. This paper compares the advantages and disadvantages of these arrangements.

We are developing superconducting tunnel junction devices for use as high-resolution, high- efficiency x-ray spectrometers. We have tested devices with niobium x-ray absorbing layers coupled to aluminum layers which serve as quasiparticle traps. These devices were fabricated photolithographically using a modified niobium/aluminum/niobium trilayer fabrication process. Our first devices have a very thin barrier with specific normal state resistance of 1.5 X 10^-6 (Omega) cm², and also exhibit very low leakage current of 15 nA below 200 mK. The energy resolution at 6 keV is 190 eV FWHM, and is limited both by electronic noise and by the non-linear response of the detector.

We report on tests of a prototype detector for 6-keV X-rays, using series arrays of tunnel junctions. Tests with higher-energy particles indicate an energy resolution of 4 keV, at 0.3 K and with a warm pre-amp. At lower temperatures and with a cooled FET, the resolution should approach 100 eV.

Two topics on our recent investigations into superconducting tunnel junction (STJ) detectors are discussed: the single Nb/Al-AlO_x/Al/Nb junction for high-resolution x-ray detection and the series-connected superconducting tunnel junction detectors (SCSDs) with high detection efficiency. Using a single Nb/Al-AlO_x/Al/Nb junction with rather large area of 178 X 178 micrometers ², we obtained a high energy resolution of 88 eV for 5.9-keV x- rays. The signal-to-noise ratio of the SCSD is discussed from a simple theoretical formulation of electronics, showing that the series-connected STJs can be developed as a nuclear radiation detector both with high energy resolution and high efficiency. Recent experimental results of our SCSD are also given in this paper.

The response to (alpha) - (beta) - and (gamma) -ray of bolometers made with a superconducting absorber and a germanium thermistor is experimentally investigated at temperatures around 100 mK. An unexpected effect was detected when a bolometer with a superconducting rhenium absorber is cooled in a weak magnetic field. Preliminary results on investigation of ¹⁸⁷Re decay by means of a Re-Ge (mu) -calorimeter will be presented.

We are developing a dielectric microcalorimeter for X-ray spectroscopy. We will present the results of our measurement of the dielectric permittivity, the spontaneous polarization, and the pyroelectric coefficient of the mixed-crystal quantum ferroelectric KTa(1-x)Nb(x)O3 with a doping of x = 0.012, as a function of temperature and bias voltage across the device. The effects of surface layers on the permittivity and the pyroelectric coefficient are discussed. We also show the signal results from infrared LED and alpha-particle radiation.

A status report is given on the development of a cryogenic particle detector. The elementary excitations are transitions between the two states of a Kramers doublet with a Zeeman splitting of the order of 10 exp -7 eV. Results are given for a compound detector with a mass of 120 grams. The baseline energy resolution is 8 eV rms/sq rt Hz, and it is shown that this resolution could be achieved with a very high absorber mass too. The signal rise time depends strongly on temperature, with the shortest signals found at the lowest temperature (35 ms at 30 mK). In addition a much shorter signal with 1 ms rise time can be superposed.

We have been developing thermal detectors for X-ray astronomy. These detectors have the advantages of both high energy resolution and high quantum efficiency. A practical detector operating at a temperature of 0.1 K could ideally have a resolution as good as 1 eV (FWHM). We have produced a detector with a measured resolution of 7 eV (FWHM) for 6 keV X-rays. The detailed behavior of the detector thermistor and thermal links impose limits on performance. Techniques for improving detector behavior will be discussed. We are currently constructing an instrument for launch on a sounding rocket to observe the soft X-ray emission from the interstellar medium.

The elements of a high resolution gamma-ray spectrometer, developed for observations of solar flares, are described. Emphasis is given to those aspects of the system that relate to its operation on a long duration balloon platform. The performance of the system observed in its first flight, launched from McMurdo Station, Antarctica on 10 January, 1992, is discussed. Background characteristics of the antarctic balloon environment are compared with those observed in conventional mid-latitude balloon flights and the general advantages of long duration ballooning are discussed.

A 'phoswich' created by NaI(Tl and CsI(Na) crystals that are optically coupled via irradiation with 200 MeV protons is here used to simulate the effect on a satellite of an orbit below the radiation belts that cross the South Atlantic anomaly. Preliminary analysis of these data adumbrates the noise following activation, as well as the capabilities of a digital pulse-shape discriminator.

The sun emits hard X-rays (above 10 keV) during solar flares. Imaging hard X-ray sources on the sun with spatial resolutions on the order of 1-5 arcsec and integration times of 1 sec will provide greater insight into the energy release processes during a solar flare. In these events, tremendous amounts of energy stored in the solar magnetic field are rapidly released leading to emission across the electromagnetic spectrum. Two Fourier telescope designs, a spatial modulation collimator and a rotating modulation collimator, were developed to image the full sun in hard X-rays (10-100 keV) in an end-to-end simulation. Emission profiles were derived for two hard X-ray solar flare models taken from the current solar theoretical literature and used as brightness distributions for the telescope simulations. Both our telescope models, tailored to image solar sources, were found to perform equally well, thus offering the designer significant flexibility in developing systems for space-based platforms. Given sufficient sensitive areas, Fourier telescopes are promising concepts for imaging solar hard X-rays.

We review some of the mission concepts currently being considered by NASA's Astrophysics Division to carry out future observations in the 100 - 3000 angstroms region. Examples of possible future missions include UV & visible interferometric experiments, a next generation Space Telescope and lunar-based UV instrumentation. In order to match these science objectives of these future missions with new observational techniques, critical technology needs in the ultraviolet regime have been identified. Here we describe how NASA's Astrophysics Division Advanced Programs Branch is attempting to formulate an integrated technology plan called the 'Astrotech 21' program in order to provide the technology base for these astrophysics missions of the 21st century.

An engineering model intensified CCD detector for the SOHO Coronal Diagnostics Spectrometer has been built and tested at the NASA Goddard Space Flight Center. A windowless MCP intensifier tube converts EUV radiation (30 - 65 nm) into visible light, which is focused via a lens system onto a Tektronix 1024 X 1024 CCD. Tests have been made of this engineering model to determine the following characteristics: quantum efficiency, resolution, throughput, linearity, statistical variation, readout noise, scattering, and flat-field response. In almost all respects, the detector performed as expected. This detector has been delivered, and work is underway on the flight detector.

We report on the status of the development of transmission grating elements for the AXAF Low Energy Transmission Grating (LETG). This instrument is supplied by a collaboration of the Space Research Organization in Utrecht/NL and the Max-Planck-Institute of Garching/Germany. We gave special attention of the optical quality of the gratings in order to match the high angular resolution of the AXAF telescope. The gratings have a period of 0.991 micrometers which allows the coverage of a wavelength bandwidth up to 140 angstroms. The variations of the period over the grating area and among different elements are less than 0.025% (RMS). The bar-width is half of the grating period (within tolerances of 50 nm) for the suppression of the even order intensities. The thickness (> 0.4 micrometers ) is adjusted in order to yield the proper phase-grating effect for X-rays at 1 keV which enhances the efficiency by a factor of up to two. The gratings are freestanding held only by a coarse support mesh obscuring 20% of the area. The ability of the gratings to withstand the acoustic noise loads during a launch of the Titan IV (142 dB OAL) has already been proven by test. Since several thousand elements have to be fabricated for AXAF totally, we have developed a new method for the characterization. This method implies the measurement of the transmittance of the grating for polarized light in its resonance domain. We show that all relevant grating parameters can be derived from this measurement. The grating facets will be assembled to 'modules', which, in turn are mounted onto the structure of the LETG. The mounting of the facets to the module require an extreme precision. A special alignment device was developed at MPI which allows the mounting of the elements with an accuracy (regarding rotation and tilt) of a few arcsec.

We have calibrated a high resolution EUV spectrometer in three spectroscopic orders using the National Institute for Science and Technology's Synchrotron Ultraviolet Radiation Facility (SURF-II) at Gaithersburg, MD. The spectrometer was the principal instrument on a University of Colorado sounding rocket experiment, with a first order bandpass of roughly 5.8 nm centered at 155.5 nm, and resolving power of 4 X 10⁴. Synchrotron radiation provides a well calibrated, columnated and polarized light source well suited to photometric calibration. The spectral distribution of synchrotron radiation is extremely well known from the theory of synchrotron radiation, and the spectral shape and intensity are directly related to the electron beam energy and current. If the instrument is calibrated at as many different beam energies as there are spectroscopic orders, then the spectrometer efficiency in each order can be determined from a single set of simultaneous equations. A difficulty arises in that the system of equations can be sensitive to perturbations of the level of experimental uncertainty. We have been able to reduce the number of unknowns by independently determining the first order efficiency and thus overdetermine the set of equations. The resulting efficiency measurements are accurate and reliable.

Most methods of producing grazing incidence optics require expensive metrology equipment to achieve sub arcminute quality in the X-ray. At the University of Colorado we have been developing methods of manufacturing grazing incidence optics by grinding and polishing on aluminum and nickel surfaces that have been machined to within a few arcminutes on a conventional metal working lathe. The mirrors are tested during fabrication by the knife edge and Ronchi test which are simple optical tests requiring only a collimated source of visible light and a 50 line per inch screen, (Gallagher 1990). No metrology of the surface is done. At graze angles of a few degrees fabricating optics by this method is limited by diffraction of the highly obstructed pupil, but at visible wavelengths figuring to 10 or 20 arcseconds is still possible. This method cannot produce arcsecond quality X-ray mirrors by itself, but can be modified to do so when coupled with normal incidence testing of the optical surface by use of a reference test plate or profilometer. In this paper we only discuss the X-ray testing of a 218 mm diameter F/5.73 Wolter Type I telescope manufactured at the University of Colorado. The mirror flew on a NASA sounding rocket in March of 1991. Testing of the inplane and offplane imaging response at energies of .25 - 1.50 KeV and correlation with surface figure are discussed.

A prototype for a small rotational modulation collimator (RMC) x-ray imaging instrument has been built and tested in the laboratory. The design and capabilities of the instrument are related to applications such as the mapping of auroral x-ray emissions from earth-orbiting platforms, as well as ground-based remote sensing. The prototype has allowed investigation of the engineering and operational problems presented by the RMC imaging concept.

For various domains, from nuclear physics to cosmology, the low temperature methods present the advantage of possibly meeting two essential objectives: a massive amount of detecting material and a high energy sensitivity to particle stopping and induced processes. A large volume of a superconducting Vanadium absorber (V approximately 2 cm³), coupled to a superconducting Iridium transition edge thermometer has been used as a phonon detector at a temperature of T_b equals 120 mK. The phonon signals read out from the device were generated by the absorption of alpha-particles emitted from an Am/Cm/Pu nuclide source. Apart from the measured energy resolution of 95 KeV FWHM for a 5.48 MeV alpha- particle, the pulse height spectra exhibit events of lower energies. Subsequent investigations indicate that the low energy events originate from processes uncorrelated to the particle interaction.

The scientific model of the SAX Medium Energy Gas Scintillation Proportional Counter has been tested at the PANTER X-ray facility in Munich. For part of the test the detector has been coupled to a representative reduced model of the SAX concentrators model. The results from the tests on both the detector and the detector/mirror assembly are within the expected performances. We have measured an energy resolution of about 8% (FWHM) and an angular resolution (on axis) of 1.3 arcminutes (HPR) at 6.4 keV.

We present the performance characteristics of a High Tech scientific model of the High Pressure Gas Scintillation Proportional Counter (HPGSPC) that has been developed as a prototype detector for the Italian X-ray Astronomy satellite SAX. We give some insight on the technology employed and we give an outline of one of the main areas of interest for the HPGSPC in the framework of the SAX mission.