Engineering topics

Moseley, S. H.

Publications and source records attributed to Moseley, S. H..

106 records · Page 6

NASA NTRS1986

Airborne spectrophotometry of P/Halley from 20 to 65 microns

Simultaneous 20 to 65 microns spectrometry and 100 microns photometry of P/Halley obtained on board the Kuiper Airborne Observatory (KAO) in 1985 Dec. and 1986 April are discussed. Spectra with resolution 30 to 50 were obtained with the NASA/Goddard 24 channel grating spectrometer. Measurements were made on the nucleus as well as 5 points along and perpendicular to the Sun-tail direction. The observations reveal the absence of any strong spectral features. The color temperature of the dust varies over time scales as short as 2 days, but is higher than that expected for a rapidly rotating blackbody at the same distance from the Sun. The color temperature does not vary within 1 arcmin of the nucleus, but the coma is brighter on the sunward side than on the antisunward side.

Glaccum, W.↗

NASA NTRS1986

High-Resolution Thermal X-Ray Detector

Thermal pulses from single photons measured. Detector, consists of X-ray absorber, temperature sensor in absorber, and thermal link from absorber to heat sink. X-ray photon detected by measuring temperature rise immediately following absorption of photon. Thermal X-ray detector, tested successfully in prototype, in theory operates as spectrometer that provides 100 times spectral resolution of conventional to detect trace constituents in materials by X-ray fluorescence. Also used for measuring energies of energetic electrons and weak pulses of light.

Moseley, S. H.↗

NASA NTRS1986

Thermal detectors for high resolution spectroscopy

Cryogenic microcalorimeters can be made sensitive enough to measure the energy deposited by a single particle or X-ray photon with an accuracy of about one electron volt. It may also be possible to construct detectors of several-kilograms mass whose resolution is only a few times worse than this. Data from relatively crude test devices are in good agreement with thermal performance calculations, and a total system noise of 11 eV FWHM has been obtained for a silicon detector operating at 98 mK. Observations of 35 eV FWHM for 6-keV X-rays with a different device have been made.

Mccammon, D.↗

NASA NTRS1986

The GSFC/Wisconsin X-ray spectroscopy investigation for AXAF

A novel device is described which combines the high quantum efficiency of a photoelectric detector with the high energy resolution of a dispersive spectrometer in a system that operates simultaneously over the whole AXAF bandpass. It is basically an X-ray calorimeter, in which the temperature rise of an X-ray absorber following the deposition of energy from a single X-ray photon can be measured to an accuracy expected to be of order one part in 1000 at 6 keV.

Holt, S. S.↗

NASA NTRS1985

MgS grain component in circumstellar shells

In this letter, far-infrared spectrophotometry (30-55 microns) and photometry (53-200 microns) are presented which define, for the first time, the long wavelength limit of the previously unidentified 30 micron emission feature found in certain extreme carbon star spectra. The spectral similarities are sufficiently similar to those of solid MgS that MgS is proposed to be the band carrier. This is interpreted as the first direct evidence that chemical surface reactions occur on dust grains in circumstellar environments. The presence of MgS indicates that either the oxygen abundance is relatively low and/or the sulfur abundance is high in extreme carbon stars.

Goebel, J. H.↗

NASA NTRS1985

Laboratory infrared spectra of predicted condensates in carbon-rich stars

Laboratory spectra and mass absorption coefficients of MgS, CaS, FeS, SiS2, FeS2, Fe3C, and a commercial iron carbide are presented over the wavelength range 125-15 microns. These spectra confirm that MgS is the most likely source of the unidentified 30-micron emission in carbon-rich sources and that FeS, Fe3C, and 'iron carbide' cannot be responsible for this feature although they could contribute to the continuum in this region. CaS and FeS2 may contribute to the 30-micron feature; however, both higher resolution and higher precision astronomical observations are needed before their presence can be established. SiS2 has a peak near 22 microns and therefore cannot be a significant component of the dust in such regions.

Nuth, J. A.↗

NASA NTRS1985

Thermal detectors as single photon X-ray spectrometers

In a thermal detector employed for X-ray spectroscopy applications, the energy of an X-ray is converted to heat in a small mass, and the energy of that X-ray inferred from the size of the temperature rise. The present investigation is concerned with the possibility to make an extremely low heat capacity calorimeter which can be employed as a thermal detector. Several types of calorimeters were fabricated and tested at temperatures as low as approximately 0.05 K. The obtained devices make use of thermistors constructed of melt-doped silicon, nuclear transmutation doped (NTD) germanium, and ion-implanted silicon with a variety of materials for the support and electrical leads. The utility of these microcalorimeters as X-ray spectrometers could be verified.

Moseley, S. H.↗

NASA NTRS1984

Thermal detectors as X-ray spectrometers

Sensitive thermal detectors should be useful for measuring very small energy pulses, such as those produced by the absorption of X-ray photons. The measurement uncertainty can be very small, making the technique promising for high resolution nondispersive X-ray spectroscopy. The limits to the energy resolution of such thermal detectors are derived and used to find the resolution to be expected for a detector suitable for X-ray spectroscopy in the 100 eV to 10,000 eV range. If there is no noise in the thermalization of the X-ray, resolution better than 1 eV full width at half maximum is possible for detectors operating at 0.1 K. Energy loss in the conversion of the photon energy to heat is a potential problem. The loss mechanisms may include emission of photons or electrons, or the trapping of energy in long lived metastable states. Fluctuations in the phonon spectrum could also limit the resolution if phonon relaxation times are very long. Conceptual solutions are given for each of these possible problems.

Moseley, S. H.↗

NASA NTRS1984

Experimental tests of a single-photon calorimeter for X-ray spectroscopy

Tests have been made of a nondispersive spectroscopic X-ray detector which operates by measuring the temperature rise following absorption of a single photon. Thermal pulses from 6-keV X-rays have been observed, and the different amplitudes resulting from Mn K-alpha and K-beta events have been resolved. This device was assembled to make quantitative tests of theoretical calculations of the properties of such detectors, and its high heat capacity does not allow it to attain the very high resolution predicted for detectors made by more sophisticated, but still straightforward, techniques. Both the measured resolution of 270-eV full width at half maximum and the absolute amplitude of the response are consistent with predictions. Nonthermal effects in the thermistor limit the precision of this comparison to about 30 percent.

Mccammon, D.↗

NASA NTRS1984

Thermal detectors as X-ray spectrometers

Moseley, S. H.↗

NASA NTRS1984

Gold absorbing film for a composite bolometer

The principles governing the design of metal films are reviewed, with attention also given to the choice of metals. A description is then given of the characteristics of a bolometer with a gold absorbing film. It is demonstrated that gold is effective as an absorbing film for a millimeter bolometer operated at 1.5 K. At 1.5 K, gold is significantly better than bismuth since gold has a lower heat capacity for the absorbing film. At 0.3 K, gold and bismuth are both suitable. It is pointed out that at temperatures below 0.3 K, a superconducting absorbing film can have a heat capacity low enough not to dominate the heat capacity of the detector; for this reason, it may give better performance than a nonsuperconducting absorbing film.

Dragovan, M.↗

NASA NTRS1981

Low thermal conductance rigidizer for reducing torsional oscillations in cryogenic Dewars

A rigidizer, which provides greater rigidity against torsional oscillations, is highly resistant to radial motions, and has low thermal conductivity, has been developed to decrease vibrational levels affecting infrared detectors operated in cryostats (e.g., HD-3L Dewar) in aircraft such as NASA's Kuiper Airborne Observatory. The rigidizer is composed of two triangular elements and an intermediate support structure which joins them at the centers of their sides. The reentrant design provides a long heat path, while the triangular truss structure provides high rigidity in the horizontal plane. The structure is relatively compliant in the vertical direction, a desirable feature since the internal structure of the Dewar contracts as it cools. Rigidity in the vertical direction is provided by the neck tube. The support structure is quite compact. Several variants of the rigidizer have been fabricated, using flat sheets of G-10 fiberglass epoxy in thicknesses between 0.75-1.5 mm for the upper and lower truss assemblies, and either G-10 or stainless steel for the intermediate structure.

Harper, D. A.↗

NASA NTRS1980

High angular resolution far-infrared observations of the W3 region

A 2 x 3 arcmin region surrounding the W3 cluster of near-infrared sources and compact H II regions has been mapped at 30, 50, and 100 microns with an angular resolution of about 30 arcsec. The data have been used to produce maps of the distribution of luminosity, color temperature, and opacity in the far-infrared which are used to analyze the properties and evolutionary states of the individual compact sources in the cluster and of the molecular cloud in which they are embedded. The total luminosity of the near-infrared source W3-IRS 5 is estimated on the basis of these observations to be 200,000 solar luminosities, and it is identified as a forming O star.

Werner, M. W.↗

NASA NTRS1978

Submillimeter observations of the galactic center

A 15 by 15 arcmin region surrounding Sgr A has been mapped at a mean wavelength of 540 microns. The principal feature is a ridge about 10 arcmin long running parallel to the galactic equator and approximately centered on Sgr A but with no peak at that point. The ridge coincides with the 25- and 55-km/s clouds seen in molecular line observations. The mass of the clouds is estimated, and their positions with respect to the galactic center are discussed.

Hildebrand, R. H.↗

NASA NTRS1977

Submillimeter photometry of extragalactic objects

Submillimeter flux densities from five extragalactic objects have been measured, and upper limits set for three others. The galaxies NGC 253 and NGC 1068 have submillimeter spectra steeper than the cube of frequency. Of several source mechanisms considered for the far-infrared and submillimeter flux from NGC 1068, only thermal emission from dust at about 30 K is consistent with the data. The source of that flux, if thermal, must have a diameter of at least 5 arcsec. If one assumes radiation from dust, the masses of interstellar material derived for the central 80-arcsec diameter regions of NGC 253, NGC 1068, and NGC 5236 are, respectively, 800 million, 10 billion, and 3 billion solar masses. Measurements of submillimeter flux densities for 3C 273, BL Lac, NGC 1275, and NGC 5128 show no excess above values obtained by interpolation between radio and mid-infrared data.

Hildebrand, R. H.↗

NASA NTRS1977

Far-infrared and submillimeter observations of the planets

Broadband observations in several passbands between 30 and 500 microns of Mercury, Venus, Mars, Jupiter, Saturn, and Uranus are presented. The best agreement between the data and various thermal models of Mars, Jupiter, and Uranus is obtained with a slightly cooler absolute temperature scale than that previously adopted by Armstrong et al. (1972). The effective temperature of Uranus is 58 + or - 2 K, which is in agreement with its solar equilibrium temperature. The existence of an internal energy source for Saturn has been reconfirmed; its output must lie within the range of 0.9 to 3.2 times the absorbed solar flux. A depression exists in the spectra of Jupiter, Saturn, and Uranus between 80 and 300 microns, which may be a result of NH3 opacity.

Loewenstein, R. F.↗