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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Nucleogenic noble gas components in the Cape York iron meteorite

The paper reports data on neutron capture products of the secondary cosmic ray component, the inferred proton and neutron fluences, and the identification of double beta decay of Se-82 in heavily shielded samples of the Cape York iron meteorite. One purpose of this study is to develop a new chronometer for cosmic ray exposure, based on the nuclides I-129 (16 My half-life) and Xe-129 from low energy cosmic ray reactions on Te. The abundance ratio of these two nuclides permits the determination of an (effective) exposure age of 93 + or - 16 My, which represents the first exposure age datum of Cape York. The very small concentrations of spallogenic Ar-38 = 6.5 x 10 to the -10th cu cm STP/g in the metal and troilite (per g Fe) document the heavily shielded locations of the sample. An excess of Xe-129 in the troilite is shown to be entirely due to the decay of cosmic-ray-produced I-129. On the other hand, an inclusion in the troilite reveals the presence of Xe-129 from extinct I-129 and documents its about 4.5 Gy formation age. Mono-isotopic excess of Kr-82 is identified as due to beta-beta-decay of Se-82 with an inferred half-life of 1.0 x 10 to the 20th y. This represents the first beta-beta-decay product observed in a meteorite.

Murty, S. V. S.↗
NASA NTRS1987

Measurements of electron attachment lineshapes and cross sections at ultra-low electron energies for CF2Cl2, c-C4F6, c-C4F8 and c-C7F14

Electron-attachment cross sections are reported in the electron energy range 0-160 meV, and at energy resolutions of 7.0 and 7.5 meV (FWHM), for the molecules CF2Cl2 (dichlorodifluoromethane), c-C4F6 (perfluorocyclobutene), c-C4F8 (perfluorocyclobutane), and c-C7F14 (perfluoromethylcyclohexane). Use is made of the Kr photoionization method. Measured attachment lineshapes are deconvoluted from the spectral slit function, and are converted to cross sections by normalization through thermal attachment-rate constants. Comparisons are made with attachment cross sections derived from several independent sets of swarm-measured rate constants, and with collisional ionization (high-Rydberg attachment) data.

Chutjian, A.↗
NASA NTRS1988

Lens Antenna For Mobile/Satellite Communication

Flat, compact antenna made of stripline elements aimed at fixed elevation angle but steered electronically in azimuth. Design simplified by maintaining fixed elevation and relying on width of beam to cover desired elevation range. Need for phase shifter at each radiating element eliminated by arranging elements in circles and feeding through stripline disks called "R-KR lenses". Used in Mobile/Satellite Service, antenna mounted on top of vehicle on Earth and used to keep transmitted and received antenna beams aimed approximately toward communication satellite.

Bodnar, D. G.↗
NASA NTRS1986

The Jovian aurora: Electron or ion precipitation

High signal-to-noise spectra of the Jovian aurora at UV wavelengths obtained using the International Ultraviolet Explorer Observatory (including the brightest Jovian aurora observed to date) set strigent upper limits for sulfur and oxygen emissions, which would be associated with the precipitation of energetic heavy ions in the upper Jovian atmosphere if they were solely responsible for Jovian auroral processes. Model calculations of heavy ion precipitation and corresponding estimates of the associated sulfur and oxygen UV emissions previously carried out suggest emission values for 1304 A OI emission that are at least 30 times larger than the upper limit values set by the IUE observations reported. On the other hand the observed (feature of SII at 1256 A of 2 kR) is quite comparable to the theoretically predicted emission intensity. Taken together these observations and calculations suggest that electron as well as ion precipitation play a role in Jovian auroral processes. In light of earlier X-ray observations and in-situ plasma observations that suggest energetic heavy ion precipitation in the Jovian auroral zone, a scenario is suggested where heavy ion auroral energy deposition is concentrated at altitudes below the homopause. Electrons with energies of 10 to 30 keV are responsible for the bulk of the observable UV and EUV emissions since they deposit their energy above the methane absorbing layer defined by the homopause.

Waite, J. H., Jr.↗
NASA NTRS1987

Noble gases in diamonds - Occurrences of solarlike helium and neon

Seventeen diamond samples from diverse locations were analyzed for the contents of He, Ar, Kr, and Xe, and of their isotopes, using a Reynolds (1956) type glass mass spectrometer. The results disclosed a large spread in the He-3/He-4 ratios, ranging from values below atmospheric to close to the solar ratio. In particular, solarlike He-3/He-4 ratios were seen for an Australian colorless diamond composite and an Arkansas diamond, which also displayed solarlike neon isotopic ratios. Wide variation was also observed in the He-4/Ar-40 ratios, suggesting a complex history for the source regions and the diamond crystallization processes.

Honda, M.↗
NASA NTRS1988

On the origin of Venus' atmosphere - Possible contributions from simple component mixtures and fractionated solar wind

It is suggested that while an origin of the volatiles of the Venus atmosphere as a single, fractionated component derivable from the solar wind can account for Ar, Kr, and Xe relative abundances, it does so only with an excess of C, and perhaps of N. A similarity is noted in relative abundances between Venus volatiles and fractionated solar wind gases in the lunar regolith which implies that such a lunar-type component is a major contributor to Venus' volatiles. A variety of Venus atmosphere models is considered; these fail to explain the low Ne/Ar ratio on Venus.

Bogard, Donald D.↗
NASA NTRS1988

Measurement of electron-attachment line shapes, cross sections, and rate constants in HI and DI at ultralow electron energies

Electron-attachment cross sections are reported in the electron energy range 0-150 MeV, at an energy resolution of 6.5 MeV (full width at half maximum) for the molecules HI and DI. Use is made of the Kr photoionization method to obtain cross sections for HI, and a signal intercomparison technique to obtain cross sections and the thermal-attachment rate constant for DI. Attachment properties of the two molecules are very similar. The ratio of attachment cross sections is discussed in terms of the reduced-mass dependence of the dissociation width and the survival probability, and in terms of spectroscopic thresholds and rotational populations for attachment at 300 K. Approximate potential-energy curves for the lowest states of the neutral molecule and negative ion are given.

Alajajian, S. H.↗
NASA NTRS1988

Vaporization of ices containing S2 - Implications for comets

An effort is made to ascertain whether the S2 detected in Comet IRAS-Araki-Alcock 1983d can be stored in ices during warming, and is released during the vaporization of its water ice matrix, in view of data on the UV spectrum of S2 in Ar and Kr matrices and water ice in which the ratio of matrix or molecular ice to S2 is of the order of 500:1. The results obtained support the hypothesis that the S2:H2O ratio in the solid phase may not be a predictor of the gas phase ratio. It is concluded that similar vaporization from a cometary nucleus would not release most of the S2 contained in the ice.

Moore, M. H.↗
NASA NTRS1988

Ejection of sodium from sodium sulfide by the sputtering of the surface of Io

The mechanism by which Na is removed from the surface of Io prior to its injection into the plasma torus is investigated experimentally. Na2S films of thickness 3-8 microns were produced by spray coating an Ni substrate in a dry N2 atmosphere and subjected to sputtering by 34-keV Ar(+), Ne(+), Kr(+), or Xe(+) ions up to total doses of about 5 x 10 to the 18th ions/sq cm. The sputtering yields and mass spectra are found to be consistent with ejection of only small amounts of atomic Na and somewhat larger amounts of Na-containing molecules. It is concluded that the amount of Na ejected by magnetospheric-ion sputtering of Na2S would be insufficient to account for the amounts observed in the Io neutral cloud. A scenario involving sputtering of larger polysulfide molecules is considered.

Chrisey, D. B.↗
NASA NTRS1989

Near Hartree-Fock quality Gaussian type orbital basis sets for the first- and third-row atoms

Energy-optimized, near Hartree-Fock (NHF) quality Gaussian type orbital (GTO) basis sets are reported for the second-row (Li to Ne) and fourth-row (K to Kr) atoms. The most accurate basis sets reported for the second row are (18s 13p) sets which are with 4 micro E(H) of the numerical Hartree-Fock (NHF) results. For B to Ne basis sets with more than 15s functions are quadruple zeta in the valence space. For the second-row transition metal atoms the (20s 12p 9d) basis sets are triple zeta in the valence space and are approximately equivalent to Clementi and Roetti's accurate Slater type orbital sets. Supplementing the (20s 12p 9d) basis sets optimized for the lowest state with the 4s(2)3d(n) occupation with a diffuse d function gives self-consistent-field energy separations to the 4s(1)3d(n+1) and 3d(n+2) states which are within 100 micro E(H) of the NHF results. The most accurate basis sets for the transition metal atoms are with 30 micro E(H) of the NHF results. In addition, energy optimized sets are reported for He(3P), Li(2P) and Be(3P).

Partridge, Harry↗
NASA NTRS1988

Lunar and Planetary Science Conference, 18th, Houston, TX, Mar. 16-20, 1987, Proceedings

Papers on lunar and planetary science are presented, including petrogenesis and chemistry of lunar samples, geology and petrogenesis of the Apollo 15 landing site, lunar geology and applications, cratering records and cratering effects, differentiated meteorites, chondritic meteorites and asteroids, extraterrestrial grains, Venus, Mars, and icy satellites. The importance of lunar granite and KREEP in very high potassium basalt petrogenesis, indentifying parent plutonic rocks from lunar breccia and soil fragments, glasses in ancient and young Apollo 16 regolith breccias, the formation of the Imbrium basin, the chemistry and petrology of the Apennine Front, lunar mare ridges, studies of Rima Mozart, electromagnetic energy applications in lunar resource mining and construction, detecting a periodic signal in the terrestrial cratering record, and a search for water on the moon, are among the topics discussed. Other topics include the bidirectional reflectance properties of Fe-Ni meteorites, the nature and origin of C-rich ordinary chondrites and chondritic clasts, the dehydration kinetics of shocked serpentine, characteristics of Greenland Fe/Ni cosmic grains, electron microscopy of a hydrated interplanetary dust particle, trapping Ne, Ar, Kr, and Xe in Si2O3 smokes, gossans on Mars, and a model of the porous structure of icy satellites.

Ryder, Graham↗
NASA NTRS1988

Theoretical energies for the n = 1 and 2 states of the helium isoelectronic sequence up to Z = 100

The unified method described previously for combining high-precision nonrelativistic variational calculations with relativistic and quantum electrodynamic corrections is applied to the 1s2 1S0, 1s2s 1S0, 1s2s 1S0, 1s2s 3S1, 1s2p 1P1, and 1s2p 3P(0.1,2) states of helium-like ions. Detailed tabulations are presented for all ions in the range Z = 2-100 and are compared with a wide range of experimental data up to (Kr-34)+. The results for (U-90)+ significantly alter the recent Lamb shift measurement of Munger and Gould (1986) from 70.4 + or - 8.3 to 71.0 + or - 8.3 eV, in comparison with a revised theoretical value of 74.3 + or - 0.4 eV. The improved agreement is due to the inclusion of higher order two-electron corrections in the present work.

Drake, G. W.↗
NASA NTRS1989

Laboratory simulation of meteoritic noble gases. III - Sorption of neon, argon, krypton, and xenon on carbon - Elemental fractionation

The sorption of Ne, Ar, Kr, and Xe was studied in carbon black, acridine carbon, and diamond in an attempt to understand the origin of trapped noble gases in meteorites. The results support a model in which gases are physically adsorbed on interior surfaces formed by a pore labyrinth within amorphous carbons. The data show that: (1) the adsorption/desorption times are controlled by choke points that restrict the movement of noble gas atoms within the pore labyrinth, and (2) the physical adsorption controls the temperature behavior and elemental fractionation patterns.

Wacker, John F.↗
NASA NTRS1989

Update on terrestrial ages of Antarctic meteorites

Cosmic-ray produced Cl-36 (half-life = 3.01 x 10 to the 5th years) has been measured in 90 Antarctic meteorites by accelerator mass spectrometry. The terrestrial ages of the meteorites were calculated from the results. After excluding possible paired objects, 138 terrestrial ages from 18 different locations are available from C-14, Kr-81, and Cl-36 measurements for application to Antarctic meteorite and glaciological studies. The terrestrial ages of Allan Hills meteorites vary from 2000 years to 1 million years and are clearly longer than those of Yamato meteorites and other Antarctic meteorites. The oldest Allan Hills meteorites were found close to the eastern edge and in the southeast of the main icefield. Among all Antarctic meteorites measured to date, only L and LL chondrites have terrestrial ages older than 370,000 years.

Nishiizumi, K.↗
NASA NTRS1989

Carbon-14 activities in recently fallen meteorites and Antarctic meteorites

This paper reports C-14 measurements in meteorites using an extraction method which employs RF melting of samples as small as 0.1 g. A study of extraction of cosmic-ray-produced C-14 in samples of Bruderheim gave C-14 levels between 38 and 60 dpm/kg for samples which had been preheated in air between 250 and 700 C, with a mean value of 46.8 + or - 1.4 dpm/kg. A range of values between 35 and 59 dpm/kg was found for other falls of saturated meteorites preheated to 500 C. The preheating step is shown to be effective in removing terrestrial carbon contamination. A series of samples previously dated by Kr-81 as having ages of 120-310 kyr gave C-14 levels of between less than 0.16 and 0.37 + or - 0.10 dpm/kg. These levels are consistent with levels of in situ production by cosmic rays at the earth's surface.

Jull, A. J. T.↗
NASA NTRS1989

Laser gain on 3p-3d and 3s-3p transitions and X-ray line ratios for the nitrogen isoelectronic sequence

Results are presented on calculations of the 72 levels belonging to the 2s(2)2p(3), 2s2p(4), 2p(5), 2s(2)2p(2)3s, 2s(2)2p(2)3p, and 2s(2)2p(2)3d configurations of the N I isoelectronic sequence for the ions Ar XII, Ti XVI, Fe XX, Zn XXIV, and Kr XXX, for electron densities up to 10 to the 24th/cu cm. It was found that large population inversions and gain occur between levels in the 2s(2)2p(2)3p configuration and levels in the 2s(2)2p(2)3d configuration that cannot decay to the ground configuration by an electric dipole transition. For increasing electron densities, the intensities of the X-ray transitions from the 2s(2)2p(2)3p configuration to the ground configuration decrease relative to the transitions from the 2s(2)2p(2)3s and 2s(2)2p(2)3d configurations to the ground configuration. The density dependence of these X-ray line ratios is presented.

Feldman, U.↗
NASA NTRS1989

Cosmogenic helium and volatile-rich fluid in Sierra Leone alluvial diamonds

Noble gas measurements were carried out on two identical splits of a finely powdered harshly acid-washed sample derived from fragments of a single alluvial diamond from Sierra Leone, with essentially identical results obtained for both splits. Isotopic ratios for Ar, Kr, and Xe were found to be atmospheric. Their elemental abundances were high relative to published data, owing to the effect of shock implantation in the crushing step, as was verified in a supplementary experiment. No Ne was detected above the blank level. The He-3 was exceptionally abundant, while He-4 was exceptionally depleted, possibly due to the acid wash. The He-3/He-4 ratio was anomalously high at an R/Ra value of 246 + or - 16. The results support the hypothesis that the He-3 excess in diamonds is cosmogenic.

Mcconville, P.↗
NASA NTRS1988

Ion formation by electron impact

Dissociative attachment and polar dissociation cross sections were measured for the following molecules: HC1, NO, N2O, C6H6, SiH4, Si2H6, and LiH. Direct ionization and dissociative ionization cross sections were determined for the following molecules: H2, D2, N2, O2, He, Ne, Ar, Kr, Xe, H2O, Co, CO2, CH4, SiH4, Sih4, Si2H6, N2*, and NH3. An experimental apparatus for a pulsed extraction technique was fabricated and successfully tested.

Srivastava, Santosh K.↗