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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

The fission track record of Apennine Front KREEP basalts

Whitlockite grains in two Apennine Front KREEP soil fragments contain extremely high densities of fission tracks. A new method is described in which particle tracks are examined in an actinide-poor phase bordering an actinide-rich whitlockite phase. This method clearly distinguishes the fission track contributions from other track sources; e.g., Fe-group cosmic rays, spallation recoils, and dislocations. Observed track excesses, when corrected for U- and Th-related fission sources, are 4-20 times greater than the contribution from spontaneous fission of U-238 (based on an age of 4 b.y.), and probably represent a large and variable contribution from the fission of Pu-244. These fragments may have pre-Imbrium ages, underscoring the importance of KREEP as a constituent of the pre-mare lunar crust. Track excesses are not correlated with the U or Th contents of the whitlockite grains. This behavior suggests that Pu fractionates differently from U and Th in lunar igneous KREEP.

Haines, E. L.↗
NASA NTRS1978

Rate constants for the deactivation of O/1D/ by Xe, Kr, and Ar over the range 110-330 K

The rate constants for the deactivation of O(1D) by Xe, Kr, and Ar were measured over the range 110-330 K. Only Xe had a significant temperature dependence. Its Arrhenius expression is (8.5 + or - 1.7) times 10 to the -11th power exp(-103 + or - 52)/RT cu cm/molecule-sec. The rate constants for Kr and Ar are (6.4 + or - 1.3) times 10 to the -12th power and (5.0 + or - 1.5) times 10 to the -13th power cu cm/molecule-sec, respectively. The observed trend in deactivation efficiency, Xe (greatest), Kr, Ar (least), and the observed temperature effects support the results and the spin-orbit interaction mechanism for deactivation given by Husain and co-workers.

Davidson, J. A.↗
NASA NTRS1979

Interplanetary phase scintillation and the search for very low frequency gravitational radiation

Observations of radio-wave phase scintillation are reported which used the Viking spacecraft having an earth-spacecraft link very similar to that which will be used in very low-frequency (VLF) gravitational-wave searches. The phase power-spectrum level varies by seven orders of magnitude as the sun-earth-spacecraft (elongation) angle changes from 1 to 175 deg. It is noteworthy that a broad minimum in the S-band (2.3 GHz) phase fluctuation occurs in the antisolar direction; the corresponding fractional frequency stability (square root Allan variance) is about 3 x 10 to the -14th for 1000-s integration times. A simultaneous two-frequency two-station observation indicates that the contribution to the phase fluctuation from the ionosphere is significant but dominated by the contribution from the interplanetary medium. Nondispersive tropospheric scintillation was not detected (upper limit to fractional frequency stability about 5 x 10 to the -14th). Evidently, even observations in the antisolar direction will require higher radio frequencies, phase scintillation calibration, and correlation techniques in the data processing, for detection of gravitational bursts at the anticipated strain amplitude levels of no more than 10 to the -15th.

Armstrong, J. W.↗
NASA NTRS1979

Absolute rate constants for the reaction of atomic hydrogen with ketene from 298 to 500 K

Rate constants for the reaction of atomic hydrogen with ketene have been measured at room temperature by two techniques, flash photolysis-resonance fluorescence and discharge flow-resonance fluorescence. The measured values are (6.19 + or - 1.68) x 10 to the -14th and (7.3 + or - 1.3) x 10 to the -14th cu cm/molecule/s, respectively. In addition, rate constants as a function of temperature have been measured over the range 298-500 K using the FP-RF technique. The results are best represented by the Arrhenius expression k = (1.88 + or - 1.12) x 10 to the -11th exp(-1725 + or - 190/T) cu cm/molecule/s, where the indicated errors are at the two standard deviation level.

Michael, J. V.↗
NASA NTRS1979

Rate constants for the reactions of OH with ClO, Cl2, and Cl2O at 298K

Recent concern about the depletion of stratospheric ozone by chlorine species from the decomposition of chlorofluoromethanes has emphasized the need for laboratory studies of the first reaction steps involved, especially those which control the concentration of the OH and ClO radicals in the stratosphere. Rate constants for the reactions of OH with ClO, Cl2, and Cl2O at 298 K have been determined in a discharge flow system using resonance fluoresence detection. The results are (9.1 + or - 1.3) x 10 to the -12th, (5.5 + or - 0.3) x 10 to the -14th, and (6.5 + or - 0.5) x 10 to the -12th (all in units of cu cm/sec), respectively.

Leu, M. T.↗
NASA NTRS1979

Asymptotic effective potentials for electron-hydrogen scattering

The asymptotic effective potential for electron- or positron-hydrogen elastic scattering is derived, correct to order x to the -7th, where x is the positron projectile coordinate, using the Feshbach optical potential as a starting point in the manner of Kleinman et al (1968). To order x to the -6th the potential agrees with the close-coupling results of Seaton and Steenman-Clark (1977) but not to order x to the -7th, where the present calculation gives the result + or - 213/2(x to the 7th) for electron and positron respectively. This coefficient differs considerably from the approximate value of Seaton and Steenman-Clark, and the discrepancy is traced to the omission of d states in their calculation.

Drachman, R. J.↗
NASA NTRS1979

Thorium concentrations in the lunar surface. III - Deconvolution of the Apenninus region

A technique of deconvoluting orbital-gamma ray data which improves spatial resolution and contrast has been applied to Th concentrations in the Apenninus region of the moon. The highest concentration seen from orbit has been found along the northern edge of the data track at Archimedes, requiring a component more highly fractionated in KREEP than the Apollo 15 medium-K Fra Mauro basalt. The results show generally diminishing Th levels extending outward from the Imbrium Basin, and impact penetration of basalt flows in Mare Imbrium to eject sub-mare Th-rich material. The results reinforce the hypothesis that the highlands which border and underlie the western maria contain a pre-mare layer of volcanically-derived KREEP material.

Metzger, A. E.↗
NASA NTRS1980

Field-aligned currents in the magnetospheric boundary layer

A self-consistent magnetopause-boundary layer model is constructed which contains two current layers, one for the magnetopause and one for the magnetosphere-boundary layer transition region. Field-aligned sheet currents in the boundary layer are generated by the plasma flow along the boundary layer. The magnitude of these boundary layer field-aligned currents is about 10 to the -8th A/sq m, which can be scaled along field lines to about 5 x 10 to the -6th A/sq m near the ionosphere and therefore can be identified as a possible source for the auroral sheet currents. The cross-field current density in the model is also about 10 to the -8th A/sq m, which is sufficient to excite the lower-hybrid-drift waves to produce the observed electromagnetic fluctuations in the magnetopause-boundary layer region.

Lee, L. C.↗
NASA NTRS1980

Determination of the thermal rate coefficient, products, and branching ratios for the reaction of O/+/ /D-2/ with N2

Atmosphere Explorer-C satellite measurements are used to determine rate coefficients (RCs) for the following reactions: O(+)(D-2) + N2 yields N2(+) + O (reaction 1), O(+)(D-2) + N2 yields O(+)(S-4) + N2 (reaction 2), and O(+)(D-2) + N2 yields NO(+) + N (reaction 3). Results show the RC for reaction 1 to be 1 (plus 1 or minus 0.5) x 10 to the -10th cu cm per sec, for reaction 2 to be 3 (plus 1 or minus 2) x 10 to the -11th cu cm per sec, and 3 to be less than 5.5 x 10 to the -11th cu cm per sec. It is also found that the reaction of O(+)(D-2) with N2 does not constitute a detectable source of NO(+) ions in the thermosphere.

Torr, D. G.↗
NASA NTRS1980

Helium runaways in white dwarfs

The long-term evolution of a carbon-accreting white dwarf (M = 0.5 solar mass) has been studied from the onset of accretion to the ignition of helium. The variations in the details of the helium-shell flash have been examined with respect to variations in mass accretion rate. For intermediate rates (10 to the -9th to 10 to the -8th solar mass/yr) the helium flash is potentially explosive, whereas for high rates (5 x 10 to the -8th solar mass/yr) the shell flash is relatively weak. The results are discussed in the context of the long-term evolution of novae.

Taam, R. E.↗
NASA NTRS1980

Search for far-infrared emission from young supernova remnants

A search has been conducted for 80-350 micron emission from the Tycho, Kepler, and Cas A supernova remnants. The bolometric fluxes are less than 5 x 10 to the -11th, 4 x 10 to the -12th, and 9 x 10 to the -12th W/sq m, respectively, for the entire radio shell, corresponding to luminosities less than 25,000, 1100, and 1500 solar luminosities (within 2 standard deviations). The ratio of dust to gas in Cas A is at least 10 times less than the 'normal' ratio.

Wright, E. L.↗
NASA NTRS1981

Field-aligned currents in the earth's magnetotail

Direct measurements of the plasma velocity distributions and simultaneous observations of magnetic fields are used to examine the character of field-aligned currents in the earth's magnetotail during the recovery phase of a magnetic substorm. Three contiguous field-aligned current sheets are identified at the interface between the magnetotail lobe and plasma sheet. Average current densities within these three current sheets are, in order of decreasing distance to the plasma sheet, +3.3 x 10 to the -9th, -1.3 x 10 to the -8th, and +1.1 x 10 to the -8th A/sq m, respectively.

Frank, L. A.↗
NASA NTRS1981

Far-infrared emission line and continuum observations of NGC 7027

The first observation of a fine-structure transition in NGC 7027 at wavelengths greater than 30 microns is reported. The flux in the 63.2-micron line is found to be approximately 10 to the -16th W/sq cm. It is noted that if NGC 7027 lies at 1 kpc, this corresponds to a luminosity, in the line, approximately 30 times greater than the solar luminosity. The flux of the 88.35-micron line is less than 10 to the -17th W/sq cm, and the upper limit to the line flux at 51.8 microns is found to be 10 to the -16th W/sq cm. These upper limits imply an electron density that is less than 1.6 x 10 to the 5th/cu cm. It is noted that the continuum measurements obtained support a dust temperature of 90 K with an emissivity approximately equal to the reciprocal of the square of the wavelength. The data exclude grain materials whose wavelength-dependent emissivity (the reciprocal of the wavelength raised to nth power) requires n to be outside the range between 1.6 and 2, unless the temperature varies drastically across the dust cloud

Melnick, G.↗
NASA NTRS1981

Observations of the giant radio lobes region of Centaurus A with SAS 3

Observations of the X-ray flux from the extended radio lobes of the galaxy Centaurus A obtained with the SAS 3 observatory are reported. The 15 x 15 deg region that includes the lobes was mapped by superposing data from raster scans with the horizontal tubular collimator detectors, which have a 1.7 deg FWHM circular field of view. Data obtained is consistent with the presence of superposed emission from the point sources NGC 5128 and MX 1312-42, a previously unreported source detected by the Einstein Observatory IPC. Fluxes of 4.63 + or - 0.14 x 10 to the -10th and 4.6 + or - 0.6 x 10 to the -11th ergs/sq cm per sec were measured for NGC 5128 and MX 1312-42, respectively, with best fit power law spectra of indices 0.83 + or - 0.04 and 0.62 + or - 0.10 and hydrogen column densities of 1.23 + or - 0.10 x 10 to the 23rd and 9.7 + or - 15.0 x 10 to the 21st atoms/sq cm. Results imply an upper limit of 2.9 x 10 to the 11th for the X-ray emission from the extended radio lobes of Cen A between 2 and 10 keV, which indicates a lower limit to the magnetic field in the lobes of 1.6 x 10 to the -6th gauss.

Marshall, F. J.↗
NASA NTRS1982

An estimate of the PH3, CH3D, and GeH4 abundances on Jupiter from the Voyager IRIS data at 4.5 microns

No evidence is found for large scale phosphine abundance variations over Jovian latitudes between -30 and +30 deg, in PH3, CH3D, and GeH4 abundances derived from the 2100-2250/cm region of the Voyager 1 IRIS spectra. The PH3/H2 value of (4.5 + or - 1.5) X 10 to the -7th derived from atmospheric regions corresponding to 170-200 K is 0.75 + or - 0.25 times the solar value, and suggests that the PH3/H2 ratio on Jupiter decreases with atmospheric pressure upon comparison with other PH3 determinations at 10 microns. In the 200-250 K region, CH3D/H2 and GeH4/H2 ratios of 2.0 X 10 to the -7th and 1.0 X 10 to the -9th, respectively, are derived within a factor of 2.0. Assuming a C/H value of 0.001, as derived from Voyager, the CH3D/H2 ratio obtained in this study implies a D/H ratio of 0.000018. This is in agreement with the interstellar medium value.

Drossart, P.↗
NASA NTRS1982

Photochemistry of the stratosphere of Venus - Implications for atmospheric evolution

The photochemistry of the Venus stratosphere is modeled using an updated and expanded chemical scheme along with the results of recent observations and laboratory studies. Three models, with H2 mixing ratio equal to 2 x 10 to the -5th, 5 x 10 to the -7th, and 1 x 10 to the -13th, respectively, are examined. All three models are found to satisfactorily account for the observations of CO, O2, O2(1Delta), and SO2 in the stratosphere, but only the last one may be able to account for the diurnal behavior of mesospheric CO and the UV albedo. Oxygen, derived from CO2 photolysis, is mainly consumed by CO2 recombination and oxidation of SO2 to H2SO4. The photolysis of HCl in the upper stratosphere provides a major source of odd hydrogen and free chlorine radicals, essential for the catalytic oxidation of CO. Oxidation of SO2 by O occurs in the lower stratosphere. The modeling reveals a number of interesting similarities, previously unsuspected between the chemistry of the stratosphere of Venus and that of the earth; photochemistry may have played a major role in the evolution of the atmosphere.

Yung, Y. L.↗
NASA NTRS1981

Bit error rate performance of Image Processing Facility high density tape recorders

The Image Processing Facility at the NASA/Goddard Space Flight Center uses High Density Tape Recorders (HDTR's) to transfer high volume image data and ancillary information from one system to another. For ancillary information, it is required that very low bit error rates (BER's) accompany the transfers. The facility processes about 10 to the 11th bits of image data per day from many sensors, involving 15 independent processing systems requiring the use of HDTR's. When acquired, the 16 HDTR's offered state-of-the-art performance of 1 x 10 to the -6th BER as specified. The BER requirement was later upgraded in two steps: (1) incorporating data randomizing circuitry to yield a BER of 2 x 10 to the -7th and (2) further modifying to include a bit error correction capability to attain a BER of 2 x 10 to the -9th. The total improvement factor was 500 to 1. Attention is given here to the background, technical approach, and final results of these modifications. Also discussed are the format of the data recorded by the HDTR, the magnetic tape format, the magnetic tape dropout characteristics as experienced in the Image Processing Facility, the head life history, and the reliability of the HDTR's.

Heffner, P.↗
NASA NTRS1983

Thorium concentrations in the lunar surface. IV - Deconvolution of the Mare Imbrium, Aristarchus, and adjacent regions

Several fields of orbital gamma ray spectroscopy data have been deconvolved in order to model the distribution of Th over the Mare Imbrium and northern Oceanus Procellarum portions of the Apollo 15 lunar ground track, which in combination with a prior study of the Apenninus region covers a continuous swath from 10 deg E to 60 deg W in the northwest quadrant. The crater of the Aristarchus region dominates the Th distribution, with a concentration of 20 ppm, and substantial enhancements are also found in the mare regions around Brayley and at the ejecta blankets of Timocharis and Lambert. The existence of enhanced Th concentrations in mare basalt regions suggests that reservoirs of some late stage mare basalts incorporated KREEP-rich material during formation or transit.

Etchegaray-Ramirez, M. I.↗