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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
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NASA NTRS1986

The high energy transmission grating spectrometer for AXAF

Attention is given to a high energy transmission grating spectrometer that operates over the range 0.4-8 keV, giving resolving powers of 100-1000 and effective areas of 10-200 sq cm. The instrument, which is part of the MIT high resolution X-ray spectroscopy investigation, consists of a single array of grating facets of two types: medium energy gratings of 0.6-micron period, 0.5-micron thick silver mounted behind the outer three AXAF mirrors, and high energy gratings of 0.2-micron period, 1.0-micron thick gold mounted behind the inner three mirrors. The gratings are oriented so as to correct for coma and so that the medium and high energy spectra form a shallow 'X' at the AXAF focal plane. Likely targets include normal stars, binary X-ray sources, active galactic nuclei and quasars. The HETGS can also be used to give moderate resolution spectra of slightly extended sources and monochromatic images of sources with strong lines, such as supernova remnants in nearby galaxies.

Canizares, C. R.↗
NASA NTRS1986

Advanced X-ray Astrophysics Facility (AXAF) instrumentation

The instrumentation planned for the Advanced X-ray Astrophysics Facility (AXAF), a space-based observation platform for the 1990s, is described. The AXAF will feature a grazing incidence telescope at the end of the observatory and four independently selected instruments at the other end, including: a CCD imaging spectrometer; a Bragg crystal spectrometer; and two transmission grating spectrometers located directly behind the telescope to detect first order spectral images. The instruments are currently in the definition phase to be followed by design and development starting in the late 1980s. A detailed schematic diagram of the Bragg crystal imaging spectrometer is provided.

Winkler, C. E.↗
NASA NTRS1973

An exploratory study of the microstructure of mullite fibers

Mullite fibers of three compositions, ranging from SiO2-rich to Al2O3-rich, were investigated by a number of transmission electron microscopy (TEM) techniques. The fibers were examined in the as-received condition and after subjecting them to thermal exposures as high as 142 C. The investigative techniques used included direct TEM of microtomed sections of mounted fibers and TEM of replicas of polished, chemically etched, and cathodically etched fibers. In addition, X-ray diffraction line broadening analyses was used for determining average crystallite size. A preliminary description of the microstructure of mullite fibers is given.

Santoro, G. J.↗
NASA NTRS1984

Tomographic and analog 3-D simulations using NORA

The results of two computer simulations demonstrate the feasibility of using the nonoverlapping redundant array (NORA) to form three-dimensional images of objects with X-rays. Pinholes admit the X-rays to nonoverlapping points on a detector. The object is reconstructed in the analog mode by optical correlation and in the digital mode by tomographic computations. Trials were run with a stick-figure pyramid and extended objects with out-of-focus backgrounds. Substitution of spherical optical lenses for the pinholes increased the light transmission sufficiently that objects could be easily viewed in a dark room. Out-of-focus aberrations in tomographic reconstruction could be eliminated using Chang's (1976) algorithm.

Yin, L. I.↗
NASA NTRS1983

Fungi and bacteria involved in desert varnish formation

Desert varnish is a coating of ferromanganese oxides and clays that develops on rock surfaces in arid to semi-arid regions. Active respiration but not photosynthesis was detected on varnished rock surfaces from the Sonoran Desert. Light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations, and cultivation experiments indicate that both fungi, primarily dematiaceous hyphomycetes, and bacteria are found on and within desert varnish coatings from the arid regions studied. Some fungi grow as microcolonial fungi (MCF) on rocks, and microscopic observations suggest MCF become incorporated in the varnish coating. SEM-EDAX (energy dispersive X-ray systems) analyses indicate the MCF contain 3 of the characteristic elements of varnish: iron, aluminum, and silicon. In some locations, MCF are also enriched in manganese relative to the rock substratum. Furthermore, some of the dematiaceous hyphomycetes that have been cultivated are able to oxidize manganese under laboratory conditions. It is possible that manganese-oxidizing bacteria, which are found in varnish, also play an important role in varnish formation.

Taylor-George, S.↗
NASA NTRS1981

A new method for focusing and imaging X-rays and gamma-rays with diffraction crystals

Bent diffraction crystals in which the intercrystalline-plane spacing is varied as a function of position in the crystal are used to focus monochromatic radiation from a point source or parallel beam down to a point image. Conversely, radiation from a point source can be focused into an outgoing parallel beam. The Bragg angle for diffraction of monochromatic radiation will now vary as a function of position in the crystal and this new degree of freedom is used to obtain focusing and imaging of the diffracted beam. This approach to focusing and imaging is applied to the design of a large-area, high resolution X-ray telescope that is also a high resolution monochromator with the unique feature that the width of the energy increment that is diffracted can be controlled and varied during the operation of the instrument. The field can be scanned with a wide energy increment and then switched to a narrow energy increment for the high resolution work. Both transmission and reflection type diffraction crystals can be used.

Smither, R. K.↗
NASA NTRS1972

A versatile Mossbauer spectrometer and its applications in vibration measurement

A Fe-57 Mossbauer spectrometer, equally efficient in transmission and reflection geometries, is described. The radiation detector consists of a 1.524- by 5.08 by 5.08-cm rectangular NaI(Tl) crystal with a hole 1.524 cm in diameter. The front and back faces of the crystal are covered with beryllium windows 0.0127 cm thick and 3.81 cm in diameter. The energy of the radiation accepted for counting ranges from 6.3 keV conversion X-rays to the 14.4 keV reemitted gamma rays. The spectrometer was used to measure various types of low frequency (10 Hz) and low amplitude (0.254 mm) periodic motion of steel specimens.

Singh, J. J.↗
NASA NTRS1980

Image Properties of an X-Ray Telescope of the Wolter-1 Type with Emphasis on Contrast Reduction by Diffuse Reflection

Theoretical and experimental results are presented on the geometrical-optic imaging properties of a Wolter-1 type paraboloid-hyperboloid X-ray telescope. Particular consideration is given to the effect of microroughness of the mirror on the imaging properties. Experiments were conducted in which scattering properties were determined as a function of wavelength, incidence angle, and roughness of the plane mirrors. Results indicate the need for optimization of mirror material and polishing technology as well as the development of improved mirror manufacturing techniques. The use of transmission gratings along with the Wolter-1 type telescope in spectroscopy applications is discussed.

Lenzen, R.↗
NASA NTRS1971

A focusing collector for long wavelength X-ray astronomy.

Rocket studies of the low-energy X-ray sky conducted so far suffer from serious experimental problems. Therefore, an apparatus was design ed to overcome the outstanding experimental problems. The instrument developed was successfully flown in an Aerobee-170 rocket. The new device utilizes a grazing incidence paraboloid as an energy concentrator and low-pass filter. The effective bandpass of the instrument from 100 to 280 eV is determined by the combination of the counter window transmission and the mirror reflectivity.

Yentis, D. J.↗
NASA NTRS1985

X-ray satellite

An overview of the second quarter 1985 development of the X-ray satellite project is presented. It is shown that the project is proceeding according to plan and that the projected launch date of September 9, 1987 is on schedule. An overview of the work completed and underway on the systems, subsystems, payload, assembly, ground equipment and interfaces is presented. Problem areas shown include cost increases in the area of focal instrumentation, the star sensor light scattering requirements, and postponements in the data transmission subsystems.

Source record↗
NASA NTRS1986

The Advanced X-ray Astrophysics Facility high resolution camera

The HRC (High Resolution Camera) is a photon counting instrument to be flown on the Advanced X-Ray Astrophysics Facility (AXAF). It is a large field of view, high angular resolution, detector for the X-ray telescope. The HRC consists of a CsI coated microchannel plate (MCP) acting as a soft X-ray photocathode, followed by a second MCP for high electronic gain. The MCPs are readout by a crossed grid of resistively coupled wires to provide high spatial resolution along with timing and pulse height data. The instrument will be used in two modes, as a direct imaging detector with a limiting sensitivity of 10 to the -15th ergs/sq cm sec in a 10 to the 5th second exposure, and as a readout for an objective transmission grating providing spectral resolution of several hundreds to thousands.

Murray, Stephen S.↗
NASA NTRS1985

Observation of hard X-rays from the Crab pulsar and A0535+26

The Crab pulsar PSR0531+21 was observed in a balloon flight from the Xianghe Balloon Station (China). Data were obtained in the range 20 to 200 keV with a poswish hard X-ray telescope which comprised a 150 sq cm primary crystal of 5 mm thick CsI(T1) which actively shielded the lower 2 pi steradians by a 5 cm thick NaI(T1) crystal. The scintillation pulses originating in CsI and NaI crystals are distinguished by pulse shape discrimination. The telescope has a field of view of approximately 4 deg H psi H pi determined by graded shield and collimator. The effective geometric area of the detector is 116 sq cm. It is noted that when folding a data flow on a long period interference from the data acquisition, transmission and recording system considerably affect the result.

Wu, M.↗
NASA NTRS1978

Coded aperture imaging with uniformly redundant arrays

The paper discusses uniformly redundant arrays (URA) as applied to coded aperture imaging. The URA system offers the high-transmission characteristics of random arrays as well as a flat sidelobe advantage. The high-transmission yields the imaging of very low-intensity sources and the flat sidelobes provide the suppression of inherent noise which obscures low-contrast sources. Simulations have shown that the URA with shot and background noise produces a better reconstructed object than random arrays without shot or background noise. The URA also offers an arrangement which involves a mosaic of basic URA patterns forming a circular correlation of the object on the picture plane. Thus the information needed to reconstruct the object is contained in an area equal to that of the basic aperture pattern. This smaller required detector is important in applications including X-ray astronomy.

Fenimore, E. E.↗
NASA NTRS1968

Imaging slitless spectrometer for X-ray astronomy

Imaging slitless spectrometer, a combination of an X ray transmission /or reflection/ grating and image-forming X ray telescope, is capable of obtaining simultaneous spatial and spectral information about celestial X ray sources.

Gursky, H.↗
NASA NTRS1972

Microscopic observations of X-ray and gamma-ray induced decomposition of ammonium perchlorate crystals

The X-ray and gamma-ray induced decomposition of ammonium perchlorate was studied by optical, transmission, and scanning electron microscopy. This material is a commonly used oxidizer in solid propellents which could be employed in deep-space probes, and where they will be subjected to a variety of radiations for as long as ten years. In some respects the radiation-induced damage closely resembles the effects produced by thermal decomposition, but in other respects the results differ markedly. Similar radiation and thermal effects include the following: (1) irregular or ill-defined circular etch pits are formed in both cases; (2) approximately the same size pits are produced; (3) the pit density is similar; (4) the c face is considerably more reactive than the m face; and (5) most importantly, many of the etch pits are aligned in crystallographic directions which are the same for thermal or radiolytic decomposition. Thus, dislocations play an important role in the radiolytic decomposition process.

Herley, P. J.↗
NASA NTRS1980

Large-aperture high-resolution X-ray collimator for the Solar Maximum Mission

A description is presented of a flight-qualified large-aperture 12 x 12-arcsec angular resolution multigrid X-ray collimator developed for the Solar Maximum Mission (SMM) flat crystal spectrometer. This collimator, designed for the 1.4-22.4-A wavelength range, utilizes an optical bench/metering structure to align and support prealigned grid subassemblies. The optical bench is a lightweight, rigid, and stable aluminum honeycomb structure. The grids are of a compound and bimetallic design, having 63.5-micron square holes on an 88.9-micron spacing in 8-micron thick gold, which is in turn supported by a 76-micron thick Invar grid having 600-micron square holes on a 739-micron spacing. The small apertures in the gold provide the 12-arcsec collimation with the Invar grids providing wide angle off-axis blocking out to an approximately 35 arcmin view angle. The collimator has seven individual channels, four of a 5.1- x 10-cm area and three of a 1.3- x 10-cm area. Laboratory measurements gave an average angular resolution of 12.5 arcsec FWHM with 0.259 transmission for the large-area channels and 12.0 arcsec and 0.200 transmission for the small-area channels. A thermal filter composed of two layers of approximately 1000-A thick aluminum prevents solar heating of the front collimator grids by absorbing longer wavelength radiation while passing most of the X radiation in the band of interest.

Nobles, R. A.↗
NASA NTRS1984

Optical fibers and components experiment (A0138-7)

Fiber optics permanent damages induced by ionizing radiation after a long exposure in space and after laboratory tests were examined. Irradiation tests performed with radioactive sources (Sr90 - Y90) were validataed, computer coses used for the fluence and dose profile were verified. The performance of fiber optics waveguides in a low altitude orbit, and the origin of transmission losses in the material were dtermined. High sensitivity to ionizing radiations, however, may be a restriction for optic fiber use on satellites. Irradiation tests on these components using neutrons, gamma rays, and X-rays are carried out. Radiation damage on opticao materials, however, is strongly linked to the test conditions.

Bourrieau, J.↗