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At least 271 records · Page 15
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NASA NTRS1988

Methane line parameters from 3700 to 4136/cm

The positions and strengths of about 1900 absorption lines of methane between 3700 and 4136/cm were measured experimentally to provide a reference line list for the identification of weak CH4 features in planetary spectra. The line parameters were obtained at room temperature with accuracies of 0.0002-0.003/cm for positions and + or - 3-40 percent for strengths using spectra recorded at 0.011/cm resolution (unapodized) with a Fourier transform spectrometer at Kitt Peak National Observatory/National Solar Observatory. Individual line strengths range from 0.00002-0.013/sq cm per atm at room temperature, and the sum of the observed strengths is 1.42/sq cm per atm at 297 K. All measurements are reported in natural isotopic abundance.

Brown, Linda R.↗
NASA NTRS1988

The search for an identification of amino acids, nucleobases and nucleosides in samples returned from Mars

The Mars Sample Return mission will provide us with a unique source of material from our solar system; material which could advance our knowledge of the processes of chemical evolution. As has been pointed out, Mars geological investigations based on the Viking datasets have shown that primordial Mars was in many biologically important ways similar to the primordial Earth; the presence of surface liquid water, moderate surface temperatures, and atmosphere of carbon dioxide and nitrogen, and high geothermal heat flow. Indeed, it would seem that conditions on Earth and Mars were fundamentally similar during the first one billion years or so. As has been pointed out, Mars may well contain the best preserved record of the events that transpired on the early planets. Examination of that early record will involve searching for many things, from microfossils to isotopic abundance data. We propose an investigation of the returned Mars samples for biologically important organic compounds, with emphases on amino acids, the purine and pyrimidine bases, and nucleosides.

Gehrke, Charles W.↗
NASA NTRS1988

Solar wind record in the lunar regolith - Nitrogen and noble gases

The measured elemental and isotopic abundances of noble gases and nitrogen have been measured in five different samples of lunar regolith material. It was found noble gases liberated by chemical attack on grain surfaces from two of the samples were solar. The Ne-20/Ne-22 ratio in the two grain surface reservoir is 13.5-13.6, compared to the average value of 13.7 + or - 0.3 measured in the Apollo solar wind collection foils (Gochsler and Geiss, 1977). It is suggested that the noble gases in grain interiors have suffered severe mass fractionation. The surface-sited N/Ar in an ilmenite sample exceeds the predicted solar ratio by more than a factor of 10. It is concluded that the solar system abundances of Cameron (1982) describe the elemental composition of the noble gases in the solar wind very well.

Frick, Urs↗
NASA NTRS1988

Cosmic-ray-produced Kr in St. Severin core AIII

Kr isotopic abundances in 10 samples from core AIII of the St. Severin chondrite are reported, and the variation with depth of cosmic-ray produced Kr is discussed. It is shown that the ratio (Kr-78/Kr-83)c changes with depth and can be used as an irradiation hardness monitor. Cosmic-ray-produced Kr and Ne in the St. Severin core are compared with ratios observed in bulk chondrites. A linear correlation between (Ne-22/Ne-21)c and (Kr-78/Kr-83)c exists for bulk samples of chondrites of varying preatmospheric size, but does not exist in the St. Severin core. The calculated Kr-83 production rates, P83, are similar in H, L, and LL chondrites for samples of comparable shielding conditions. However, P83 rates increase by a factor of about 2 with shielding depth. The maximum observed P83 values correspond to (Kr-78/Kr-83)c factor of about 2 with shielding depth. The maximum observed P83 values correspond to (Kr-78/Kr-83)c less than about 0.14.

Lavielle, B.↗
NASA NTRS1990

Carbon isotopes in comets

The progress is reported of high resolution spectra of selected bright comets with the aim of determining the carbon isotope abundance ratio, C-12/C-13. The ratio was determined for various Solar System objects (in the atmospheres of the giant planets, meteorites, the Earth, and the solar photosphere), where the C-12/C-13 = 89/1. In the interstellar medium, optical and radio observations give a range of C-12/C-13 = 43-67/1 depending on the observing techniques used and the specific interstellar cloud observed. The echelle spectra is presented of the CN(0,0) violet system in three comets: P/Brorsen-Metcalf, C/Okazaki-Levy-Rudenko, and C/Austin. P/Brorsen-Metcalf has a period of 70 y (prograde) compared with P/Halley which is 76 y (retrograde). The similar periods made P/Brorsen-Metcalf of special interest for comparison with P/Halley.

Wehinger, Peter A.↗
NASA NTRS1991

Oxygen extraction from lunar soil by fluorination

Mining and processing of lunar material could possibly lead to more cost-efficient scenarios for permanent presence of man in space and on the Moon. Production of oxygen for use as propellant seems especially important. Different candidate processes for oxygen-extraction from lunar soil were proposed, of which the reduction of ilmenite by hydrogen was studied most. This process, however, needs the concentration of ilmenite from lunar regolith to a large extent and releases oxygen only with low efficiency. Another possibility - the fluorination method - which works with lunar bulk material as feedstock is discussed. Liberation of oxygen from silicate or oxide materials by fluorination methods has been applied in geoscience since the early sixties. The fact that even at moderate temperatures 98 to 100 percent yields can be attained, suggests that fluorination of lunar regolith could be an effective way of propellant production. Lunar soil contains about 50 percent oxygen by weight which is gained nearly completely through this process as O2 gas. The second-most element Si is liberated as gaseous SiF4. It could be used for production of Si-metal and fluorine-recycling. All other main elements of lunar soil will be converted into solid fluorides which also can be used for metal-production and fluorine-recycling. Preliminary results of small scale experiments with different materials are discussed, giving information on specific oxygen-yields and amounts of by-products as functions of temperature. These experiments were performed with an already existing fluorine extraction and collection device at the University of Bonn, normally used for determination of oxygen-isotopic abundances. Optimum conditions, especially concerning energy consumption, are investigated. Extrapolation of the experimental results to large industrial-type plants on the Moon is tried and seems to be promising at first sight. The recycling of the fluorine is, however, crucial for the process. It might be achieved by means of electrolysis. This needs further investigation. The technical problem of transport and handling of the toxic and corrosive fluorine seems to be solvable and could be done by inert storage vessels.

Seboldt, W.↗
NASA NTRS1990

Primary and diagenetic controls of isotopic compositions of iron-formation carbonates

Results are presented on parallel analyses of carbonate and chert microbands in segments from the early Proterozoic Dales Gorge Member of the Brockman Iron Formation (western Australia), including data on isotopic, chemical, and mineralogic variations in microbanded carbonates, cherts, and coexisting minerals in four core segments from Paraburdoo and one from Wittenoom. It is shown that patterns of variation observed in isotopic abundance and mineral composition can be consistently explained in terms of diagenetic replacement of fine-grained primary precipitates by secondary ones, rather than by mineral-dependent fractionations, metamorphism, or the influence of large volumes of water in an open system.

Kaufman, Alan J.↗
NASA NTRS1991

Noble gases in 'phase Q' - Closed-system etching of an Allende residue

Results are presented from an analysis, in nearly pure form, of noble gases from the 'phase-Q' in an HF/HCl residue of the Allende C3V meteorite, using the closed-system stepped etching technique developed by Wieler et al. (1986) and Benkert et al. (1988) to extract noble gases from the residue. The results yield precise values of element and isotope abundances of all five noble gases in phase-Q, which is the major carrier of the planetary gases in carbonaceous chondrites. It was found that Ne-Q and Xe-Q in Allende are very similar to trapped gases in ureilites and in oxidizable carriers in several classes of ordinary chandrites, indicating that Q-gases are present in the formation locations of all these meteorites.

Wieler, Rainer↗
NASA NTRS1992

Mars volatile evolution: Implications of the recent measurement of O-17 in water from the SNC meteorites

Oxygen, carbon, and hydrocarbon isotopes in water and carbon dioxide in the Martian environment can fractionate due to processes involving escape to space, exchange between atmospheric and non-atmospheric species, and exchange of atoms between different molecules. As a result, the ratios of O-18/O-17/O-16, C-13/C-12 and D/H in atmospheric and surface species are sensitive indicators of the integrated effects of outgassing and volatile evolution over geologic time. Previously, I summarized all of the available observations of isotopic abundances and compared them with models of fractionation in order to see which scenarios of volatile evolution were most plausible. Presently, I have included in the models the possible evolution of O-17 due to loss to space in order to see whether these measurements are consistent with various scenarios for atmospheric evolution.

Jakosky, Bruce M.↗
NASA NTRS1991

s-process Ba, Nd, and Sm in presolar SiC from the Murchison meteorite

Ion microprobe isotopic measurements of Ba, Nd, and Sm in the K-series SiC size separates on which noble gas measurements were made by Lewis et al. (1990) are reported. All elements show isotopic abundance patterns characteristic for the s-process. The Ba-134/Ba-136 ratios are distinct from solar, indicating that s-Ba in SiC is different from that in the solar system. Ba-138/Ba-136 ratios decrease with grain size; if interpreted as being due to different neutron exposures, this trend is opposite of that shown by the Kr-86/Kr-82 ratios. Although other isotropic ratios for Ba and those for Nd and Sm differ in detail from theoretical predictions, the disagreements probably being due to uncertainties in the n-capture cross sections and simplifications in the models, the general agreement of the data with models of s-process nucleosynthesis support an AGB star origin for the relatively fine-grain SiC under consideration. Ba-136 in SiC is up to 85 percent pure s-process.

Zinner, Ernst↗
NASA NTRS1992

Stable isotope analysis using tunable diode laser spectroscopy

Ratios of C-12/C-13 in CO2 have been measured using a tunable diode laser (TDL) spectrometer to an accuracy of better than 0.4 percent. These results were made possible by the use of state-of-the-art high-temperature TDLs, an etalon and wavenumber calibration technique, high-speed assembly language controlled data acquisition, and the ratioing of absorbances from simultaneously acquired sample and reference data scans. The dual beam spectrometer that is employed uses the sweep integration technique in a spectral region where adjacent spectral lines are of approximately equal absorbance at the expected isotopic abundances.

Becker, Joseph F.↗
NASA NTRS1992

Venusian hydrology: Steady state reconsidered

In 1987, Grinspoon proposed that the data on hydrogen abundance, isotopic composition, and escape rate were consistent with the hypothesis that water on Venus might be in steady state rather than monotonic decline since the dawn of time. This conclusion was partially based on a derived water lifetime against nonthermal escape of approximately 10(exp 8) yr. De Bergh et al., preferring the earlier Pioneer Venus value of 200 ppm water to the significantly lower value detected by Bezard et al., found H2O lifetimes of greater than 10(exp 9) yr. Donahue and Hodges derived H2O lifetimes of 0.4-5 x 10 (exp 9) yr. Both these analyses used estimates of H escape flux between 0.4 x 10(exp 7) and 1 x 10(exp 7) cm(exp -2)s(exp -1) from Rodriguez et al. Yet in more recent Monte Carlo modeling, Hodges and Tinsley found an escape flux due to charge exchange with hot H(+) of 2.8 x 10(exp 7) cm(exp -2)s(exp -1). McElroy et al. estimated an escape flux of 8 x 10(exp 6) cm(exp -2)s(exp -1) from collisions with hot O produced by dissociative recombination of O2(+). Brace et al. estimated an escape flux of 5 x 10(exp 6) cm(exp -2)s(exp -1) from ion escape from the ionotail of Venus. The combined estimated escape flux from all these processes is approximately 4 x 10(exp 7) cm(exp -2)s(exp -1). The most sophisticated analysis to date of near-IR radiation from Venus' nightside reveals a water mixing ratio of approximately 30 ppm, suggesting a lifetime against escape for water of less than 10(exp 8) yr. Large uncertainties remain in these quantities, yet the data point toward a steady state. Further evaluation of these uncertainties, and new evolutionary modeling incorporating estimates of the outgassing rate from post-Magellan estimates of the volcanic resurfacing rate are presented.

Grinspoon, David H.↗
NASA NTRS1992

CELIAS: Charge, Element and Isotope Analysis System for the SOHO mission

The status and further development as well as first calibration of the CELIAS experiment on SOHO is presented. CELIAS is designed to measure the mass, ionic charge, and energy of low and high speed solar wind of suprathermal ions and of low energy flare particles. Through analysis of the elemental and isotopic abundances (the ionic charge state and velocity distributions of ions originating on the solar atmosphere), the investigation focuses on studying the plasma processes in various temporal and spatial scales in the solar chromosphere, transition zone, and corona. Additionally, the CELIAS experiment includes the Solar EUV Monitor (SEM). This unit, which consists of an EUV transmission grating spectrometer and three isolated silicon photodiodes as detectors, is described. The three mass and charge discriminating sensors based on the time of flight technique are also described.

Hovestadt, D.↗
NASA NTRS1992

On the accuracy of CO line positions for high resolution IR stellar spectroscopy

The paper demonstrates the high accuracy of line positions derived from improved sets of Dunham coefficients for the four more abundant isotopic species of carbon monoxide - (C-12)(O-16), (C-13)(O-16), (C-12)(O-18), and (C-12)(O-17) - which are present in the sun and in cool stellar atmospheres. These new spectroscopic constants make it possible to predict very accurate positions of CO lines at any J-values, especially at very high rotational excitation (up to J around 135). Earlier proposed identifications of CO lines at large J-values are checked, and some incorrect identifications in sunspot spectra are found. The present accurate line positions are also compared with predictions from other available sets of molecular constants. It is concluded that the present improved sets of molecular constants are the most appropriate to all problems of high-resolution stellar and solar spectroscopy at any J- and v-values, particularly for synthetic spectra of cool stars.

Sauval, A. J.↗
NASA NTRS1993

The elemental and isotopic composition of Galactic cosmic-ray nuclei from scandium through nickel

Measurements of the relative elemental and isotopic abundances of iron-group Galactic cosmic rays at energies of about 325 MeV per nucleon have been made. The source abundance ratio of Ni-60/Ni-58 is 1.07 +/- 0.39, which is a factor of 2.8 +/- 1.0 larger than the solar system value. Our measurements imply the presence of Co-59 at the source, which can be reconciled with the predictions of conventional nucleosynthesis models if there exists a time delay of more than about 100,000 yr between nucleosynthesis and acceleration. Most of the Mn-54 produced by spallation during cosmic-ray propagation in the Galaxy is found to have decayed to Fe-54, indicating a confinement time of greater than 2 Myr. The source ratio of Fe-54/Fe-56 corrected for the Mn-54 decay is 0.046+/- 0.020, which is consistent with the solar system value of 0.063.

Leske, Richard A.↗
NASA NTRS1994

The cometary flourescence spectrum of cyanogen: A model

We present a model to compute flourescence spectra of the stable isotopes of CN in the comae of comets. The effects of collisions are included and shown to be significant as a mechanism secondary to the flourescence process in the calculations. Our computed spectra are compared with high-resolution spectra of the B2 sigma(+)-X2 sigma(+) (0-0) band for comets Halley, Austin, and Levy. This comparison shows that collisonal effects are observable in the CN spectra of relatively high production rate comets, such as Halley and Levy. Moreover, the model confirms that the overall structure of the CN spectra in comets results predominantly from pure flourescence governed by the Swings effect. The primary goal of our model is to provide a methodology to compute accurate rotational line flourescence efficiencies for the stable isotopes of CN: (12)C(14)N, (13)C(14)N, and (12)C(15)N. The flourescence efficiencies are required to convert observed isotope line intensity ratios to isotope abundance ratios of carbons and nitrogen in comets.

Kleine, Marvin↗
NASA NTRS1999

Particle Acceleration at the Sun and in the Heliosphere

Energetic particles are accelerated in rich profusion at sites throughout the heliosphere. They come from solar flares in the low corona, from shock waves driven outward by coronal mass ejections (CMEs), from planetary magnetospheres and bow shocks. They come from corotating interaction regions (CIRs) produced by high-speed streams in the solar wind, and from the heliospheric termination shock at the outer edge of the heliospheric cavity. We sample all these populations near Earth, but can distinguish them readily by their element and isotope abundances, ionization states, energy spectra, angular distributions and time behavior. Remote spacecraft have probed the spatial distributions of the particles and examined new sources in situ. Most acceleration sources can be "seen" only by direct observation of the particles; few photons are produced at these sites. Wave-particle interactions are an essential feature in acceleration sources and, for shock acceleration, new evidence of energetic-proton-generated waves has come from abundance variations and from local cross-field scattering. Element abundances often tell us the physics the source plasma itself, prior to acceleration. By comparing different populations, we learn more about the sources, and about the physics of acceleration and transport, than we can possibly learn from one source alone.

Reames, Donald V.↗
NASA NTRS2003

New Measurements of the Li, Be, and B Isotopes as a Test of Cosmic Ray Transport Models

Precise measurements of predominantly secondary cosmic-ray Li, Be, and B together with current well-measured production cross-sections for these isotopes help to improve our understanding of galactic cosmic ray propagation models. The Cosmic Ray Isotope Spectrometer (CRIS) on ACE has been measuring isotopic composition of cosmic rays since 1997 with high statistical precision. We present the isotopic abundances from CRIS and discuss these observations in the context of cosmic-ray transport models and previous cosmic-ray measurements.

deNolfo, Georgia A.↗