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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Time-dependent local density measurements in unsteady flows

A laser-induced fluorescence technique for measuring the relative time-dependent density fluctuations in unsteady or turbulent flows is demonstrated. Using a 1.5-W continuous-wave Kr(+) laser, measurements have been obtained in 0.1-mm diameter by 1-mm-long sampling volumes in a Mach 3 flow of N2 seeded with biacetyl vapor. A signal amplitude resolution of 2% was achieved for a detection frequency bandwidth of 10 kHz. The measurement uncertainty was found to be dominated by noise behaving as photon statistical noise. The practical limits of signal-to-noise ratios have been characterized for a wide range of detection frequency bandwidths that encompasses those of interest in supersonic turbulence measurements.

Mckenzie, R. L.↗
NASA NTRS1978

Excess fission xenon at Apollo 16

Results are reported of stepwise heating analyses of Xe and Kr in four Apollo 16 low-grade breccias: 60019, 60225, 60275, and 67455. All four samples contain significant amounts of solar wind gases and at least three contain excess fission Xe. This observation indicates that the excess fission Xe effect is global rather than local, i.e., results from moon-wide redistribution of fission Xe rather than local redistribution in KREEP-rich Apollo 14 material. It is suggested that the excess fission Xe phenomenon represents a temporal variation in the amount of fission Xe available for redistribution, that it is prominent in samples from both highland sites simply because they are older than mare sites, and that samples from these sites had experienced at least some of their surface exposure at an early epoch.

Bernatowicz, T. J.↗
NASA NTRS1979

Composition and structure of the Venus atmosphere - Results from Pioneer Venus

The composition of the Venusian atmosphere was studied using a mass spectrometer on the Pioneer Venus sounder probe. The single-focusing magnetic-sector spectrometer scanned the mass range from hydrogen through mercury with a dynamic range of six decades. Data taken by the mass spectrometer were compared with those of a gas chromatograph, resulting in slight discrepancies due to the use of a sputter ion pump acting as a sink for entry of rare gases through the inlet leak. A surprisingly large concentration of primordial Ar-36 and Ar-38 was discovered in a ratio of 5 to 1. It was concluded that the large excess of primordial argon was a valid result and that the mixing of HCl in the lower Venusian atmosphere was less than a few parts per million. Arguments against the sun as the source for excess primordial gases on Venus were presented. Concentrations of other elements such as Ne, Kr, He, S, and O were discussed. Although the mass peaks in the spectrum were real, it was not clear whether all of the chemical reactions (i.e., COS production) actually occurred in the atmosphere. Until further analysis can be made, it will be uncertain how the inlet system, which is at atmospheric temperature, affected the results.

Hoffman, J. H.↗
NASA NTRS1979

Isotopic anomalies of noble gases in meteorites and their origins. IV - C3 /Ornans/ carbonaceous chondrites

The C3O chondrites Kainsaz, Lance, and Ornans were studied by an acid dissolution technique to characterize the noble gas components in 3 mineral fractions: HF, HCl-solubles, chromite and carbon, and 'phase Q', a trace mineral containing Ar, Kr, Xe. For all fractions, gas contents decline in the order Kainsaz, Lance, Ornans; this trend parallels volatile contents but not heterogeneity of olivine composition or degree of metamorphism, and reflects progressively higher condensation temperature from the solar nebula. The Ar/Xe ratios and compositions of the three mineral fractions are discussed, and it is concluded that in all primitive chondrites the amount and the chemical separability of CCFXe parallel the abundance of primordial noble gases and other volatiles, such as C, N, Tl, Bi, and In. The close correlation of CCFXe with properties of local origin, such as volatile content and petrologic type, is more consistent with a local than with an extrasolar origin of the component.

Alaerts, L.↗
NASA NTRS1979

Volume-pumped nuclear lasers

A summary is given to experimental results on volume-pumped nuclear lasers obtained at the Langley Research Center. The first volume-pumped nuclear laser was achieved in 1976 using the He-3(n, p)H-3 reaction. Since that time laser output has increased by more than a factor of 1000 (from mW to W). Lasing has been demonstrated in He-3-Ar (1.27 and 1.79 micron), He-3-Xe (2.027, 3.5, and 3.65 microns), He-3-Kr (2.19 and 2.52 microns), and He-3-Cl (1.587 micron). Pressures of the lasing mixture range from 300 torr to 4 atm with a peak power output of 26 W were achieved in a He-3-Ar mixture with a multiple-pass laser configuration.

Hohl, F.↗
NASA NTRS1979

Nuclear pumped laser modeling

A model for an indirectly nuclear pumped laser experiment was developed. The apparatus consists of the usual cylindrical neutron moderator enclosing a gas filled quartz cell. The quartz cell in this case has two concentric compartments; the larger output compartment is filled with He-3 and fluorescent gases which are coupled radiatively to the inner compartment which is filled with a lasing gas for efficient optical pumping. The fluorescent gas in this study was a mixture of Ar, Kr and F2. Perfluoroalkyliodide was chosen as the lasant material of the inner compartment. The degree of photoabsorption in the lasant gas was calculated. The kinetic efficiencies of various gas combinations in the outer fluorescence tube were then evaluated in order to maximize the fluorescence output in the iodine pump band.

Wilson, J. W.↗
NASA NTRS1979

Stellar condensates in meteorites - Isotopic evidence from noble gases

The Murchison carbonaceous chondrite contains three isotopically anomalous noble-gas components of apparently presolar origin: two kinds of Ne-E, (Ne-20)/(Ne-22) less than 0.6, and s-process Kr + Xe (enriched in the even isotopes 82, 84, 86, 128, 130, 132). Their carriers are tentatively identified as spinel and two carbonaceous phases, the principal high-temperature stellar condensates at low and high C/O ratios, respectively.

Lewis, R. S.↗
NASA NTRS1980

Isotopic anomalies of noble gases in meteorites and their origins. VI Presolar components in the Murchison C2 chondrite

Rare gases were analyzed by stepped heating in five fractions of a chemically resistant residue from Murchison that had been separated according to grain size and resistance to HClO4. Nine gas components were recognized, of which three appear to be presolar: (1) Ne-E(H) released at 1000-1600 C and located in spinel; (2) Ne-E(L) released at less than 800 C and apparently located in a carbonaceous phase of grain size up to 10 microns; and (3) s-process Xe and Kr released at 1200-1600 C and located in a poorly characterized, possibly carbonaceous phase, distinct from the host phase of Ne-E(L).

Alaerts, L.↗
NASA NTRS1980

Noble-gas-rich separates from ordinary chondrites

Acid-resistant residues were prepared by HCl-HF demineralization of three H-type ordinary chondrites: Brownfield 1937 (H3), Dimmitt (H3, 4), and Estacado (H6). These residues were found to contain a large proportion of the planetary-type trapped Ar, Kr, and Xe in the meteorites. The similarity of these acid residues to those from carbonaceous chondrites and LL-type ordinary chondrites suggests that the same phase carries the trapped noble gases in all these diverse meteorite types. Because the H group represents a large fraction of all meteorites, this result indicates that the gas-rich carrier phase is as universal as the trapped noble-gas component itself. When treated with an oxidizing etchant, the acid residues lost almost all their complement of noble gases.

Moniot, R. K.↗
NASA NTRS1979

Xenon from intermediate zones of supernovae

The paper examines the photodisintegration and neutron capture in massive stars which show that the bulk of the p-isotopes of Xe is formed during the gamma-process of Woosley and Howard (1978) by stripping of the Xe + Be seeds. The environments in which the chondrites can be formed were determined by the neutron-capture calculations; they show that the Xe-124-rich gas must be associated at the sources with anomalously large overabundances of Nd-142, Sm-144, and possibly Ba-130, and with anomalously small overabundances of the p-isotopes of Se, Kr, Sr, and Mo.

Heymann, D.↗
NASA NTRS1980

Spectra from nuclear-excited plasmas

The paper discusses the spectra taken from He-3(n,p)H-3 nuclear-induced plasmas under high thermal neutron flux, lasing conditions. Also, initial spectra are presented for U-235F6 generated plasmas. From an evaluation of these spectra, important atomic and molecular processes that occur in the plasma can be inferred. The spectra presented are the first to be generated by He-3 and U-235F6 nuclear reactions under high neutron flux, lasing conditions. The U-235(n,ff)FF reaction, which liberates 165 MeV of fission-fragment kinetic energy, creates plasmas that are of great interest, since at sufficiently high densities of U-235F6 the gas becomes self-critical; thus, there is no need for an external driving reactor (source of neutrons). The spectra from mixtures of He-3 and Ar, Xe, Kr, Ne, Cl2, F2 and N2 indicate little difference between high-pressure nuclear-induced plasmas and high-pressure electrically pulsed afterglow plasmas for noble-gas systems

De Young, R. J.↗
NASA NTRS1980

Fabry-Perot-interferometer imaging system for thermospheric temperature and wind measurements

Doppler-broadened Fabry-Perot fringes of weak (less than 1-kR) auroral forbidden O I 5577- and 6300-A emissions have been detected in real time (1/60 sec) with the aid of a low-light level image-orthicon TV camera coupled to a two-stage image intensifier. The imaging scheme permits static-mode operation of a Fabry-Perot interferometer. For maximum use of all the information contained in every TV frame, each circular fringe may be sectioned into several annuli, and the corresponding annuli from all rings are summed to yield an intensity value. This procedure for deriving a fringe profile requires a video digitizer coupled to a digital processing system and should provide fast real-time (1/60 sec) measurements of E- and F-region temperatures and winds. With forbidden O I 5577-A intensity of 750 R, visually prominent TV images of the Fabry-Perot fringes were recorded in 0.5 sec, and the temperature of the emitting region was determined from two percent of the total information in the TV image.

Sivjee, G. G.↗
NASA NTRS1980

Spatial imaging of hydrogen Lyman-alpha emission from Jupiter

A sounding rocket measurement of the H I L-alpha emission from Jupiter made on Dec. 1, 1978 shows limb darkening and an average disk brightness of 13 kR. This brightness is significantly higher than in previous measurements, and was confirmed by an IUE observation on Dec. 10, 1978. Comparison with a plane-parallel hydrogen layer model indicates that there is enhanced emission from the equatorial regions, reaching a peak near 80 deg longitude.

Clarke, J. T.↗
NASA NTRS1980

Cosmic ray exposure ages of chondrites, pre-irradiation and constancy of cosmic ray flux in the past

Calibration of the production rate of the Ne-21 nuclide was accomplished by 4 methods based on (Al-26)-age, (Mn-53)-age, Kr-81/Kr-83, and Na-22/Ne-22. These production rates are normalized to a shielding parameter ratio Ne-22/Ne-21 = 1.11 and to the chemical composition of L chondrites; a value of P(21)(1.11) = 0.31 is suggested, and a production rate equation derived in terms of the 'F' parameters for L, LL, and H chondrites. The Al-26 half-life measurements are considered to evaluate the effects resulting from preirradiation of meteorites and to examine the data on the constancy of the cosmic ray flux in the light of current astronomical observations.

Nishizumi, K.↗
NASA NTRS1980

Pioneer Venus gas chromatography of the lower atmosphere of Venus

A gas chromatograph mounted in the Pioneer Venus sounder probe measured the chemical composition of the atmosphere of Venus at three altitudes. Ne, N2, O2, Ar, CO, H2O, SO2, and CO2 were measured, and upper limits set for H2, COS, H2S, CH4, Kr, N2O, C2H4, C2H6, and C3H8. Simulation studies have provided indirect evidence for sulfuric acid-like droplets and support the possibility of water vapor at altitudes of 42 and 24 km. The paper discusses the implications of these results for the origin, evolution, and present state of Venus' atmosphere.

Oyama, V. I.↗
NASA NTRS1981

IUE detection of bursts of H Ly-alpha emission from Saturn

A new investigation is reported of the potential sources of Ly-alpha emission in a series of observations of the Saturnian system carried out between January and July 1980 using the short wavelength spectrograph of the IUE Observatory. It is noted that north-south maps of the Ly-alpha emission across the planet disk show pronounced spatial asymmetries in emission brightness. These asymmetries vary to a marked extent on a time scale of days and are interpreted as bursts of Ly-alpha emission of as much as 1 kR brightness averaged over a 6 x 10 arcsec area, above a constant planetary emission level of 700-800 R. In fact, the Ly-alpha emission peaks manifest themselves as essentially point source features in these data; it is pointed out that if the emitting region is smaller than the 6 x 10 arcsec instrumental resolution, the surface brightness must be proportionally higher.

Clarke, J. T.↗
NASA NTRS1981

Excitation cross sections for krypton by electrons in the 15-100-eV impact-energy range

Differential, integral, and momentum-transfer cross sections have been determined for the excitation of the 24 lowest electronic states of Kr (some of the transitions are unresolved). The inelastic-scattering cross sections were normalized to the absolute scale with the help of the elastic-scattering differential cross sections (DCS's) which in turn were normalized with respect to absolute He DCS's. The impact energies were 15, 20, 30, 50, and 100 eV and the DCS's were obtained over the range of 5-135 deg scattering angles. The error limits associated with the differential, integral, and momentum-transfer cross sections have been estimated at 25%, 38%, and 46%, respectively.

Trajmar, S.↗
NASA NTRS1981

Spectroscopy of the Cameron bands in the Mars airglow

Mars airglow spectra obtained by the ultraviolet spectrometer on board the Mariner 9 spacecraft were analyzed by using a high-resolution synthesis of the observed emissions. Bright limb observations were made of altitudes between 88 and 180 km of which the brightest features are the carbon monoxide Cameron bands in the wavelength region 1800-2600 A. The shape of these bands cannot be characterized by a single rotational temperature, but is best described by temperatures of 1600 K for lower J values and 10,000 K for higher J values. The observed zenith intensity of 16.7 kR is in good agreement with an excitation theory in which electron-impact dissociation is the most important mechanism. The observations suggest the value of the cross section for this process should be 7 x 10 to the -17th/sq cm. The first negative bands of CO(+) are not identified in the Mariner 9 spectra. This is consistent with the excitation theory for these bands.

Conway, R. R.↗