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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Impurity color centers in quartz and trapped electron dating - Electron spin resonance, thermoluminescence studies.

Investigation of impurity-related electron-hole traps that are known to be sensitive to ionizing radiations. Electron spin resonance (ESR) equivalent natural doses were determined for the Al hole trap in virgin specimens; the doses agreed with estimates based on published data for the Ge electron trap. The 0.17 deg/sec 180 and 300 C thermoluminescence (TL) peaks in natural specimens were found to have activation energies approximately correct for the Ge trap. The 300 C peak was also found to be correlated with annealing of the Ge electron resonance in gamma-irradiated, step-annealed specimens. Although the 300 C peak occurs in virgin specimens, the corresponding natural Ge electron resonance was not observed.

Mcmorris, D. W.↗
NASA NTRS1994

One-dimensional multispecies hydrodynamic models of the wakeside ionosphere of Titan

The passage of Voyager 1 through the wakeside region of Titan's ionosphere provided an interesting probe of this plasma environment. A one-dimensional multispecies hydrodynamic model was developed to study the wakeside ionosphere for radial distances ranging from 1.3 to 4.5 R(sub T) and included the ion species H2CN(+), C(sub n) H(sub m)(+), C2H5(+), CH5(+), H(+), H2(+), and H3(+). Plasma transport only along magnetic field lines was included. The only source of ion production was from electron impact ionization of Titan's atmosphere by radially streaming Saturnian magnetospheric electrons (i.e., the nightside wakeside ionosphere). We found that ion production rates due to hot (200 eV) magnetospheric electrons impacting Titan's neutral atmosphere along radial field lines were comparable to the dayside ion production rates due to solar EUV flux. The magnetic flux tube area was varied along with electron temperature, and the results were compared to the ion densities and velocities measured during the Voyager 1 encounter. We found outward ion flows of about (2 to 7 x 10(exp 6)/sq cm/s, resulting in a total ion loss from Titan into Saturn's magnetosphere of about (6 to 20) x 10(exp 24)/s.

Keller, C. N.↗
NASA NTRS1981

On the maintenance of the Venus nightside ionosphere - Electron precipitation and plasma transport

The relative contributions of electron precipitation and transport of dayside plasma to the maintenance of the Venus nightside ionosphere during the long Venusian night are investigated based on simultaneous Pioneer Venus Orbiter Retarding Potential Analyzer measurements of suprathermal electron fluxes and plasma densities. In about 20 orbits, the nightside integral electron flux of electrons with energies between 5 and 45 eV is observed to be relatively constant in time and altitude, while plasma density is observed to vary by a factor of 10 or more with no correlation with the electron flux. Ionization rates and ion density height profiles are computed for O(+) and O2(+) as a function of magnetic dip angle based on a typical electron spectrum, or a downward flux of O(+) ions. Comparison of the computed profiles with the measured median O(+) and O2(+) density profiles reveals that the measured profiles can only be reproduced by a downward flux of O(+) equal to about 10 to the 8th/sq cm per sec; suprathermal electron energy distributions produce O2(+) and O(+) levels only about half and one tenth those usually observed, respectively. It is thus concluded that transport of O(+) ions from the dayside Venus ionosphere is responsible for approximately 75% of the typical nightside ionization, with variations in O(+) transport mechanism responsible for most of the observed nightside density variations. The remaining ionization is attributed to suprathermal electrons, which contribute principally to the O2(+) peak.

Spenner, K.↗
NASA NTRS1975

Electron density profiles from ionograms - Underlying ionization corrections and their comparison with rocket results

Electron density profiles from nine daytime rocket flights at Wallops Island, Va., conducted at high and low levels of solar activity are compared with profiles calculated by inversion of ionograms obtained at the same times and location. Sources of error and uncertainty in the ionogram inversion are discussed, as are means for their amelioration. In most cases, agreement between the two kinds of measurement within a few percent in electron density and within a few percent of a scale height can be achieved.

Wright, J. W.↗
NASA NTRS1985

X-ray secondary heating and ionization in quasar emission-line clouds

Accurate Monte Carlo computations of the X-ray secondary electron heating, ionization, and excitation of H and He gas in interstellar space and in quasar emission-line clouds, are presented. The fraction of energy deposited in each form is sensitive to the background ionization fraction, x = n(H+)/n(Htot), and can affect the temperature, ionization state, and line emissivities at large depths in X-ray photoionized clouds. Analytic fits are provided for these energy fractions over the range 0.0001-1 for primary electron energies up to many keV. In both broad-line and narrow-line clouds, emission lines sensitive to the energy budget and electron density may be strongly affected.

Shull, J. M.↗
NASA NTRS1994

Al III, Si IV, and C IV absorption toward zeta Ophiuchi: Evidence for photionized and collisionally ionized gas

We present Goddard High-Resolution Spectrograph observations at 3.5 km/s resolution and signal-to-noise ratios of 30 to 60 for the Al III, Si IV, and N V absorption lines in the far-ultraviolet spectrum of the O9.5 V star zeat Ophiuchi. The measurement reveal three types of highly ionized gas along the 140 pc line of sight. (1) Narrow components of Al III (b = 4.3 km/s, the mean value of (v(helio)) = -7.8 km/s; b = 3.2 km/s, the mean value of (v(sub helio)) = -14.4 km/s) and Si IV (b = 5.3 km/s, the mean value of (v(sub helio)) = -15.0 km/s) trace photionized gas in the expanding H II region surrounding zeta Oph. The observed magnitude and direction of the velocity offset between the Al III and Si IV profiles can be explained by models of H II regions that incorporate expansion. Narrow C IV absorption associated with the H II region is not detected. Predictions of the expected amounts of Si IV and C IV overestimate the column densities of these ions by factors of 30 and more than 10, respectively. The discrepancy may be due to the effects of elemental depletions in the gas and/or to the interaction of the stellar wind with surrounding matter. (2) Broad (b = 15 to 18 km/s) and weak Si IV and C IV absorption components are detected near the mean value of (v(sub helio)) = -26 km/s. The high-ionization species associated with these absorption components are probably produced by electron collisional ionization in a heated gas. This absorption may be physically related to the zeta Oph bow shock ot to a cloud complex situated within the local interstellar medium at d less than 60 pc. The C IV to Si IV column density ratio in this gas is 8, a factor of 6 less than conductive interface models predict, but this discrepancy may be removed by considering the effects of self-photoionization within the cooling gas in the model calculations. (3) A broad (b = 13 km/s) and weak C IV absorption feature detected at the mean value of (v(sub helio)) = -61 km/s is not seen in other species. We tentatively ascribe this absorption to gas in a postshock ragion of an optically thin shock in the zeta Oph stellar wind.

Sembach, Kenneth R.↗
NASA NTRS1995

Theoretical study of hole initiated impact ionization in bulk silicon and GaAs using a wave-vector-dependent numerical transition rate formulation within an ensemble Monte Carlo calculation

In this paper, calculations of the hole initiated interband impact ionization rate in bulk silicon and GaAs are presented based on an ensemble Monte Carlo simulation with the inclusion of a wave-vector-dependent numerical transition rate formulation. The ionization transition rate is determined for each of the three valence bands, heavy, light, and split-off, using Fermi's golden rule with a two-body, screened Coulomb interaction. The dielectric function used within the calculation is assumed to be wave-vector-dependent. Calculations of the field-dependent impact ionization rate as well as the quantum yield are presented. It is found from both the quantum yield results and examination of the hole distribution function that the effective threshold energy for hole initiated impact ionization is relatively soft, similar to that predicted for the corresponding electron initiated ionization events occur more frequently than either heavy or split-offf initiated ionization events in bulk silicon over the applied electric field strengths examined here, 250-500 kV/cm. Conversely,in GaAs, the vast majority of hole initated ionization events originate from holes within the split-off band.

Oguzman, Ismail H.↗
NASA NTRS1974

Conduction in fully ionized liquid metals

Electron transport is considered in high-density fully ionized liquid metals. Ionic structure is described in terms of hard-sphere-correlation functions and the scattering is determined from self-consistently screened point ions. Applications to the physical properties of the deep interior of Jupiter are briefly considered.

Stevenson, D. J.↗
NASA NTRS1991

Cross sections for direct and dissociative ionization of NH3 and CS2 by electron impact

A crossed electron beam-molecular beam collision geometry is used to measure cross sections for the production of positive ions by electron impact on NH3 and CS2. Ionization cross-section data for NH3 and the values of various cross sections are presented, as well as ionization efficiency curves for CS2. Considerable differences are found between the various results on NH3. The present values are close to the data of Djuric et al. (1981). The semiempirical calculations of Hare and Meath (1987) differ considerably in the absolute values of cross sections. Discrepancies were observed in comparisons of cross sections of other fragment ions resulting from the ionization and dissociate ionization of NH3.

Rao, M. V. V. S.↗
NASA NTRS1985

Energy partitioning in the Io plasma torus

The Io plasma torus, which emits substantial amounts of EUV radiation from multiply ionized oxygen and sulfur, represents one of the significant discoveries of the Voyager 1 mission. The present study is concerned with the effects of various physical processes on the density and energy partitioning of the Io plasma torus. For the ions the dominant effects, which have different relative importance in different parameter regimes, are electron impact ionization, charge exchange, electron-ion collisions, and confinement time loss. Attention is given to a physical model, the solution of the quasi-linear equations, the obtained results, and an interpretation of observations in relation to the model results.

Smith, R. A.↗
NASA NTRS1982

Single and multiple ionization of sulfur atoms by electron impact

In 1979 significant concentrations of singly and multiply charged sulfur ions were observed in the Io torus. Attempts to model these observations revealed a need for new fundamental cross section data. In response, laboratory measurements of the cross-sections for single, double, triple and quadruple ionization of sulfur atoms by electron impact are presented for collision energies from threshold to 500 eV.

Ziegler, D. L.↗