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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 127 records · Page 7
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NASA NTRS1973

Conjugate photoelectron excitation of O I 4368 airglow emission.

Conjugate photoelectron fluxes are shown to be mainly responsible for the excitation of O I 4368 radiation observed with a grille spectrometer located at Langmuir Laboratory, New Mexico (L equals 1.7). On the basis of observations of O I 7774 and 4368 tropical emissions at Agulhas, Negras, Brazil (L equals 1.1), the contribution of radiative recombination to the New Mexico intensity is shown to be small. Conjugate photoelectron excitation at the Brazilian site has not been observed.

Christensen, A. B.↗
NASA NTRS1973

Fabrication and properties of gallium phosphide variable colour displays

The unique properties of single-junction gallium phosphide devices incorporating both red and green radiative recombination centers were investigated in application to the fabrication of monolithic 5 x 7 displays capable of displaying symbolic and alphanumeric information in a multicolor format. A number of potentially suitable material preparation techniques were evaluated in terms of both material properties and device performance. Optimum results were obtained for double liquid-phase-epitaxial process in which an open-tube dipping technique was used for n-layer growth and a sealed tipping procedure for subsequent p-layer growth. It was demonstrated that to prepare devices exhibiting a satisfactory range of dominant wavelengths which can be perceived as distinct emission colors extending from the red through green region of the visible spectrum involves a compromise between the material properties necessary for efficient red emission and those considered optimum for efficient green emission.

Effer, D.↗
NASA NTRS1973

Jovian ionospheric models

This paper reports results obtained on ionosphere formation in the Jovian upper atmosphere with special reference to some of the recently available reaction rates, and to recent models of the Jovian neutral atmosphere based on the possibility of a warmer mesopause. In the older models of the Jovian ionosphere, the major ions were H+ which were lost only by pure radiative recombination. This led to high electron densities and practically no diurnal change. In contrast, recent models have relatively much smaller electron densities, especially in lower regions, and may be susceptible to significant diurnal variation.

Capone, L. A.↗
NASA NTRS1974

Boltzmann equation for the electron gas of a nondegenerate plasma

The collision terms in the Boltzmann equation associated with various processes are derived. For processes having a Fokker-Planck (F-P) limit, the associated F-P operator is derived by means of physical arguments to determine the form of the operator; its multiplying constant is fixed by calculating the total energy exchange rate and comparing with the rate computed by other means. In this manner, the F-P operator is derived for electron-ion scattering, electron-electron scattering in the high-velocity limit, electron-atom elastic scattering, Compton scattering, and the high-velocity limit for inelastic scattering. Other processes considered are bremsstrahlung, radiative-recombination, photoionization, collisional ionization of atoms, and suprathermal-particle ionization of atoms.

Gould, R. J.↗
NASA NTRS1974

Effect of inelastic electron-atom collisions on the Balmer decrement

Calculation of the Balmer decrement in radiatively ionized hydrogen gas as a function of temperature and density, taking into account the effect of electron-atom collisions. It is found that once the electron density exceeds 10 to the 10th power per cu cm significant deviations from the normal radiative recombination decrement begin to occur. Implications of these results for the physical conditions in the line-emitting region of the Seyfert galaxy NGC 4151 are discussed briefly.

Adams, W. M.↗
NASA NTRS1975

Laser processes in plasmadynamic flows

Radiation emitted from the exhaust flow of a multi-megawatt, quasi-steady magnetoplasmadynamic accelerator has been examined photoelectrically for argon mass flows from 6 to 32 g/sec and arc currents up to 25 kA. Vacuum ultraviolet radiation, indicative of resonance transitions, has been detected photoelectrically at various axial locations downstream of the arc chamber, consistent with a relaxation length calculated using a collisional-radiative recombination model. Photoelectric measurements of particular transitions in the neutral and first ionic state of argon show that populations of excited electronic states of AII are in excess of that which would be expected on the basis of Saha-Boltzmann equilibrium at the local electron temperature and number density. Optical depth measurements indicate that for a current of 4 kA and argon mass flow of 12 g/sec, a population inversion exists between the upper and lower states of the 0.4880 micron argon ion transition.

Campbell, E. M.↗
NASA NTRS1975

The 1640.4 A H-alpha line of He II observed from Skylab

Profiles obtained from NRL Skylab solar spectra of the 1640.4 A feature identified as the H-alpha line of He II are discussed and compared with theoretical profiles derived assuming (1) collisional excitation and (2) radiative recombination as the dominant excitation mechanism. Relative intensities of this line as a function of altitude above and below the solar white-light limb are also given for a representative quiet sun region and for a polar coronal hole.

Feldman, U.↗
NASA NTRS1976

Nitric oxide gamma band emission in an aurora

Emission of the NO gamma (1,0) band at 2150 A has been observed by a rocket-borne spectrophotometer in an IBC II(+) aurora. The nu-prime progression of the gamma-system does not appear in the spectrum. The observed emission rate of the 2150 A feature increases relative to N2(+) first negative band emission with increasing altitude. We suggest radiative recombination of NO(+) ions with electrons as a possible excitation mechanism compatible with the data.

Feldman, P. D.↗
NASA NTRS1976

The solar XUV spectrum of He II

OSO-7 observations of the first five Lyman lines and the Lyman continuum of He II are given for the quiet sun, a coronal hole, prominences, filaments, and the flare of August 7, 1972. These data are calibrated and given in specific intensity units together with color and brightness temperatures for the He II continuum. It is found that He II is overionized in all features except the flare and that the continuum is formed at temperatures near 14,000 K. The He II-He III ionization equilibrium appears to be dominated by photoionizations and radiative recombinations. Schematic calculations for realistic chromosphere and transition-region models can account for the observed intensities of Ly-beta through Ly-epsilon, the Lyman continuum, and its color temperature. To account for the intensity of Ly-alpha, either an implausible 100-km plateau at temperatures near 80,000 K is needed or, more likely, the diffusion-enhanced collisional excitation should be incorporated into the models.

Linsky, J. L.↗
NASA NTRS1976

X-ray spectra of the Puppis A and the Vela supernova remnants

Low-energy X-ray spectra are presented for the entire Vela supernova remnant (SNR), the two most intense subregions of the Vela SNR, and the Puppis A SNR. Acceptable chi-squared fits are obtained from the model of a high-temperature low-density plasma with Allen cosmic abundances when thermal bremsstrahlung, radiative recombination, line emission, and interstellar absorption are included. A suggested increase of 45-fold in the Si abundance for the entire Vela SNR is found unacceptable by chi-squared tests of the present spectra. The two enhanced regions of Vela are found to have different temperatures. A deficiency of at least a factor of 3 is seen in the O VII and O VIII emission from the entire Vela SNR. Because ultraviolet observations indicate a normal abundance of oxygen, this is interpreted as evidence for the existence of nonequilibrium conditions in the emitting plasma.

Moore, W. E.↗
NASA NTRS1976

Tropical F region winds from O I 1356-A and forbidden OI 6300-A emissions. I - Theory

The paper theoretically investigates the relationship of neutral winds and E x B plasma drifts to the time-dependent distribution of 1356-A and 6300-A airglow intensities in the region of the Appleton anomaly. Radiative recombination, ion-ion neutralization, and dissociative recombination are considered as main mechanisms in producing the atomic oxygen tropical nightglow. A quantitative relation is determined between the neutral wind velocities and the resultant asymmetry in the emissions about the dip equator. The height difference at northern and southern conjugate points is shown to be linearly related to the vector sum of the wind velocity components along the magnetic meridian at the latitude of the conjugate points. The height difference at conjugate points may be used to study the pattern of neutral wind velocities in the tropical ionosphere.

Bittencourt, J. A.↗
NASA NTRS1976

Formation of the 0.511 MeV line in solar flares

The slowing down and annihilation of positrons and the formation of positronium in a solar flare plasma are investigated to determine how the width of the 0.511-MeV line and its strength relative to the three-photon continuum from positronium decay depend on the temperature and density of the medium in which the positron comes to rest. The calculations are limited to the cases of annihilation in a completely ionized plasma, in a partially ionized plasma with an electron/neutron density ratio of 1.0 or 0.1, and in an atomic gas with a very small ion density. Thermally averaged rate coefficients are obtained for the free annihilation of positrons and for positronium formation through radiative recombination in the fully ionized plasma. Positronium formation rates and the resultant energy distributions of the positronium atoms in the partially ionized medium are determined by numerically solving the Fokker-Planck equation in a medium where the ambient free electrons have a Maxwell-Boltzmann distribution of finite temperature but the density of the medium is sufficiently low that positronium atoms decay without further collisions following their formation. A Monte Carlo calculation is performed for the positron energy loss, positronium formation through charge exchange, and positronium breakup in the weakly ionized medium. The energy distributions of decaying positronium atoms and the relative number of triplet to singlet positronium decays are evaluated for ion concentrations and densities characteristic of the solar photosphere.

Crannell, C. J.↗
NASA NTRS1977

Nuclear-pumped lasing of /He-3/-Xe and /He-3/-Kr

The letter reports direct nuclear pumping of (He-3)-Xe and (He-3)-Kr using the volumetric He-3(n,p)H-3 nuclear reaction. Lasing in (He-3)-Xe was achieved at the 2.027-micron transition of Xe I; lasing in (He-3)-Kr is assumed to have occurred at the 2.52-micron transition of Kr I. Experimental results show that laser output in (He-3)-Xe increases and tends to saturate with increasing pressure, the lasing neutron-flux threshold decreases with decreasing neutron pulse, and maximum output occurs between 0.1% and 0.5% Xe with the total pressure held constant at 400 torr and with an average neutron flux of 6 by 10 to the 15th power per sq cm/sec. It is noted that the (He-3)-Xe laser has the lowest lasing-threshold neutron flux of any He-3 nuclear-pumped laser to date, but the (He-3)-Kr laser has a very high threshold flux. The primary lasing mechanism is believed to be Penning ionization of Xe and Kr followed by collisional radiative recombination and cascading into the upper laser level.

De Young, R. J.↗
NASA NTRS1979

A study of the excitation and radiative decay of the 3s-prime 3D-0 and 3d 3D-0 levels of atomic oxygen

The absolute cross-sections for the excitation of the 989 A, 1027 A, 7990 A, 8446 A, 1.1287 micron and 1.3164 micron multiplets of atomic oxygen by electron impact dissociation of O2 are reported. The radiative branching ratios for these transitions are calculated from these results and compared with the NBS compilation of Wiese et al. (1966) and the recent theoretical calculations of Pradhan and Saraph (1977). The cascade models of O(+) radiative recombination and of electron-impact excitation of the O I(3S) state in the terrestrial airglow are discussed in the light of the laboratory measurements, and the effects of the resonant absorption of components of the lambda 989 A and lambda 1027 A multiplets by the Birge-Hopfield band system of N2 are investigated. This process is shown to depend sensitively on the N2 vibrational temperature and to cause characteristic changes in the OI EUV emission spectrum in auroras and in the sunlit F-region at high exospheric temperatures.

Zipf, E. C.↗
NASA NTRS1979

Ultraviolet night airglow of Venus

The night airglow spectrum of Venus in the ultraviolet is dominated by the V-prime = 0 progressions of the gamma and delta bands of nitric oxide. The bands are produced by two-body radiative recombination of nitrogen and oxygen atoms. Since the source of these atoms is in the dayside thermosphere, the night airglow is a tracer of the day-to-night thermospheric circulation. The airglow is brightest at equatorial latitudes and at longitudes on the morning side of the antisolar meridian.

Stewart, A. I.↗
NASA NTRS1979

IUE and visual spectrophotometry of 3C 120 and Markarian 79

Low-resolution ultraviolet spectra have been obtained with IUE and combined with similar visual observations. The continua of both objects show an excess of flux in the neighborhood of 3000 A. In both objects there appears to be a depression near 2200 A, which is probably the ultraviolet interstellar absorption feature centered at 2175 A. The strength of this feature suggests E(B-V) values of 0.22 and 0.38 for Mrk 79 and 3C 120, respectively. The ratio of intensities of L-alpha to H-beta is abnormally small compared with the radiative recombination ratio; the discrepancy is removed in 3C 120 and much reduced in Mrk 79 if the reddening values just mentioned are adopted. The C IV to L-alpha line intensity ratio is abnormally high in these objects compared with that for quasars. Although both objects have strong Fe II lines in the visual, there is no Fe II absorption or emission in the ultraviolet.

Oke, J. B.↗
NASA NTRS1979

Simplified model of a volumetric direct nuclear pumped He-3-Ar laser

A physical model for the volumetric nuclear pumped He-3-Ar laser is described and the source terms arising from the He-3(n, p)H-3 reaction as well as the rate equations are given. Steady state solutions are derived for the densities of the species vs the fraction of argon. The dominant pumping mechanism is found to be collisional radiative recombination of the argon atomic ions and subsequent cascading into the upper laser level. The reactions following recombination are described and an expression is derived for the difference in densities of the argon 3d and 4p levels. Comparison with experiments shows good agreement.

Harries, W. L.↗