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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Sorption of noble gases by solids, with reference to meteorites. I - Magnetite and carbon

The trapping of meteoritic noble gases by solids is simulated through the synthesis of 18 Fe3O4 samples at 350-720 K in a noble gas atmosphere, by means of the reactions: (1) 3Fe + 4H2O yields Fe3O4 + 4H2, using Ne, Ar, Kr and Xe; and (2) 3Fe + 4CO yields Fe3O4 + 4C + carbides, using Xe. Etching experiments suggest an analogy with 'Phase Q' in meteorites. Adsorbed atmospheric gases are present in all samples, and dominate whenever the noble gas partial pressure in the atmosphere is greater than that in the synthesis. While many of the results of Lancet and Anders (1973) appear to have been dominated by such an atmospheric component, others are suspect. When the doubtful samples of Lancet and Anders are corrected or eliminated, the fractionation pattern no longer peaks at Ar, but rather, as in the present sample, rises monotonically from Ne to Xe. No evidence is found for the earlier study's claim of a strong temperature dependence.

Yang, J.↗
NASA NTRS1982

Abundances in five nearby galactic H II regions from infrared forbidden lines

Airborne measurements of the Ar II (6.99 micron) and S II (18.7) micron lines for five compact H II regions in the solar neighborhood are presented, as well as 2-4 micron and 8-13 micron spectroscopy where available. From these data and radio data, lower limits to the elemental abundances of Ar, Ne, and S are deduced. Some of these H II regions suffer substantial nebular extinction, and some are extended. After correcting for beam size effects an extinction, it is found that four of the objects are consistent with standard abundances, within the uncertainties of correcting for unobserved ionization states. A Perseus arm object, S156, is apparently overabundant in sulfur.

Herter, T.↗
NASA NTRS1982

Shock disturbance of the I-Xe system

Three separate samples of the meteorite Bjurbole were artificially shocked at pressures of 70 kb, 200 kb, and 400 kb. Analysis of xenon released in stepwise heating shows that the I-Xe system of the 400 kb sample is substantially altered by the shock loading, and it is no longer possible to infer an age or trapped xenon composition for that sample. The 200-kb and 70-kb samples display isotopic structures progressively less altered demonstrating the gradations in shock disturbance likely to be found in natural systems. Interpretations of the I-Xe and Ar-40-Ar-39 systems for several naturally shocked meteorites are also presented. New data for Arapahoe do not confirm the previously reported age and trapped xenon composition, demonstrating instead that its I-Xe structure has been strongly disturbed by shock.

Caffee, M. W.↗
NASA NTRS1982

Chronology and petrogenesis of young achondrites, Shergotty, Zagami, and ALHA77005 - Late magmatism on a geologically active planet

Three achondrites were examined for chronology, petrogenesis, and relationships among the shergotites. Isotopic and trace elements analyses were carried out through neutron activation and mass spectrometry on Shergotty, Zagami, and ALHA77005 samples. Attention was given the Rb-Sr, Sm-Nd, and the Ar-39/Ar-40 ages in the samples. Evidence was detected for a shock metamorphism and a younger age of the meteorites than with most other achondrites. Depletions of the rare-earth elements were observed in Shergotty and Zagami, and to a more pronounced degree in ALHA77005. The Rb-Sr internal isochrons for all three meteorites were about 180 Myr, while the Ar-39/Ar-40 plateau ages of Shergotty and Zagami maskelynite were determined at 250-260 Myr. No precise identification of the crystallization ages was found. It is suggested that the achondrites originated in a parent body which experienced at least two epochs of sustained melting.

Shih, C.-Y.↗
NASA NTRS1982

Advances in NASA research on nuclear-pumped lasers

NASA has been primarily interested in nuclear-pumped lasers using the He-3 or U-235F6 reaction for lasant excitation. With He-3 excitation, a large volume, multiple-path He-3-Ar nuclear laser has produced an output of 1 kilowatt. Power deposition was shown to be homogeneous over this volume. The CO laser has been pumped for the first time using the He-3 reaction, producing approximately 200 Watts. Using a boron-10 coating to excite N2, nuclear lasing has been achieved in CO2 in a transfer laser configuration. Nuclear lasing of Ar-Xe has been demonstrated using fission fragment excitation from U-235F6. Research on the gas core reactor has resulted in a steady state operational power of 30 kilowatts with flowing U-235F6 in an argon vortex.

De Young, R. J.↗
NASA NTRS1983

Cataractogenesis from high-LET radiation and the Casarett model

The long-term effects on specific animal tissues of exposure to heavy ion irradiation are studied in experiments on cataractogenesis in mice and rabbits. Five groups of rabbits at ages from 8 weeks to 5.3 years were irradiated to a dose of 9.0 Gy of Bragg plateau Ne-20 ions, while mice were exposed to single and total fractionated doses of 4.17 Gy gamma rays or 0.40 to 1.20 Gy of C-12, Ne-20 or Ar-40 particles. Measurements of lens opacities over time show that in the year since irradiation, cataractogenesis is delayed and less severe in rabbits irradiated at age 6 months compared to younger animals, although it is possible that the late effects in adults will surpass those found in the young. The fractionation of the total dose of gamma rays in mice is observed to lead to a marked reduction in the extent of lens opacity after one year, while fractionated heavy ion doses caused a greater degree of posterior lens opacification. Evaluations of the effects of the LET of different ions on cataractogenesis are consistent with RBEs of about 5, 3 and 1-2 for Ar-40, Ne-20 and C-12 ions, respectively. Results thus support the Casarett model of radiation damaging stem cell populations that are not necessarily part of the vasculature.

Cox, A. B.↗
NASA NTRS1983

Late skin damage in rabbits and monkeys after exposure to particulate radiations

Preliminary results are reported of experiments on the late effects of exposure to particulate radiations on stem cell populations. Skin biopsies were taken from the ears of rabbits irradiated 2-5 years previously with 530 MeV/amu Ar ions (LET 90 keV/micron), or 365 MeV/amu Ne ions (LET 35 keV micron), and from the chests and inner thighs of rhesus monkeys irradiated 16-18 years previously with 32-MeV protons (LET about 1.2 keV/micron). Skin fibroblast cultures obtained from the biopsy samples in rabbits were observed to undergo dose-dependent decreases in in vitro life span, with estimated survival curves showing the effects of Ar-ion irradiation to be more severe than those of Ne-ion irradiation. In addition, the healing of the biopsy wound was observed to become slower as radiation dose increased. In the monkey, radiation reduced the average number of fibroblasts at the time of cessation of growth in culture. Results thus demonstrate the capacity of skin sampling to reveal stem cell destruction, and have important implications for astronauts and other persons at risk of particle exposure with regard to healing responses to trauma or surgery.

Bergtold, D. S.↗
NASA NTRS1983

The oxidation behavior of a model molybdenum/tungsten-containing alloy in air alone and in air with trace levels of NaCl(g)

Thermogravimetric, metallographic, and X-ray studies of a model alloy, Ni-(17 a/o)Al-(10 a/o)Mo+W, oxidized in dry air at 600-1200 C and in air with 10 ppm NaCl gas at 900 C, are reported. The alloy was melted under Ar and pretreated in flowing H2 for 24 h at 1300 C. Polished 1.3 x 1.3 x 0.2-cm specimens were washed and degreased prior to oxidation in a quartz tube within a furnace for up to 120 hr. The oxidation activation energy of the alloy is determined to be about 30 kcal/mole. The specimens oxidized at 900 C and hotter exhibited oxidized and nitrided phases covered by complex NiMoO4, NiWO4, and NiAl2O4 scales and a porous, nonprotective outer layer of NiO. The oxidation behavior is found to be determined by the formation and growth of the scale, especially the (Mo,W)O2 component. Al2O3 scale layers were not formed, and further runs with pure O2 or Ar-(20 percent)O2 ruled out an explanation of this phenomenon based on aluminum nitride formation. The oxidation was accelerated by the addition of NaCl gas, a finding attributed to the reaction of NaCl with external locally protective Al2O3 scales and with the internal(Mo, W)O2 layers.

Smeggil, J. G.↗
NASA NTRS1983

Trapped noble gases indicate lunar origin for Antarctic meteorite

The isotopic abundances of the noble gases (He, Ne, Ar, Kr, Xe) are reported for Antarctic ALHA 81005. It contains solar wind-implanted gases whose absolute and relative concentrations are quite similar to lunar regolith samples but not to other meteorites. ALHA 81005 also contains a large excess Ar-40 component which is identical to the component in lunar fines implanted from the lunar atmosphere. Large concentrations of cosmogenic Ne-21, Kr-82, and Xe-126 in ALHA 81005 indicate a total cosmic ray exposure age of at least 200 million years. The noble gas data alone are strong evidence for a lunar origin of this meteorite.

Bogard, D. D.↗
NASA NTRS1983

Radioactivites in returned lunar materials and in meteorites

The cosmic-ray, solar-flare, and solar-wind bombardments of lunar rocks and soils and meteorites were studied by measurements of tritium, carbon-14 and argon radioactivity. The radioactivity integrates the bombardment for a time period equal to several half-lines. H-3, Ar-37, Ar-39, C-14. For the interior samples of lunar rocks and for deep lunar soil samples, the amounts of the radioactivities were equal to those calculated for galactic cosmic-ray interactions. The top near-surface samples of lunar rocks and the shallow lunar soil samples show excess amounts of the radioactivities attributable to solar flares. Lunar soil fines contain a large amount of hydrogen due to implanted solar wind. Studies of the H-3 in lunar soils and in recovered Surveyor-3 materials gave an upper limit for the H-3/H ratio in the solar wind of 10 to the -11th power. Solar wind carbon is also implanted on lunar soil fines. Lunar soils collected on the surface contained a 0.14 component attributable to implanted solar wind C-14. The C-14/H ratio attributed to the solar wind from this C-14 excess is approximately 4 x 10 to the -11th power.

Fireman, E. L.↗
NASA NTRS1984

Radical and ion molecule mechanisms in the polymerization of hydrocarbons and chlorosilanes in RF plasmas at low pressures ( 1.0 torr)

The ion-molecule and the radical-molecule mechanisms are responsible for the dissociation of hydrocarbons, and chlorosilane monomers and the formation of polymerized species, respectively, in the plasma state of a RF discharge. In the plasma, of a mixture of monomer with Ar, the rate determining step for both dissociation and polymerization is governed by an ion-molecular type interaction. Additions of H2 or NH3 to the monomer Ar(+) mixture transforms the rate determining step from an ion-molecular interaction to a radical-molecule type interaction for both monomer dissociation and polymerization processes.

Avni, R.↗
NASA NTRS1983

Infrared observations of RS CVn stars

The paper presents infrared photometry of the RS CVn binary stars AR Lac (1.2-10 microns) and MM Her (1.2-3.5 microns) as they egressed from their primary and secondary eclipses; of the eclipsing systems RS CVn and Z Her at maximum light (1.2-10 microns) and of the non-eclipsing systems UX Ari and HR 1099 (1.2-10 microns). An analysis of these and published V data based on flux ratio diagrams (linear analogues of color-color diagrams) shows that G and K stars supply the infrared light of these systems. In AR Lac, the combined light of a G5-K0 subgiant and either a late F dwarf or an early F subgiant can account for the observed visual and infrared light curves. None of these systems shows infrared emission from circumstellar matter. This result is simply understood: dust grains would not be expected to form in the physical conditions surrounding the subgiant, and the corona and chromosphere (whose properties have been deduced from spectroscopic X-ray observations) should not produce appreciable infrared emission.

Berriman, G.↗
NASA NTRS1983

Broad-band gain in optically pumped S2

The broad fluorescence spectrum and Franck-Condon shift of the B-X system of S2 are exploited in broad-band-gain experiments using the absorption of 308-nm XeCl excimer radiation to pump the level (upsilon-prime = 4) in an S2 vapor with and without Ar. The fluorescence spectra are examined to determine the effects of gas collisions, and the intense near-UV and visible bands are attributed to the redistribution of the population among the upsilon-prime levels resulting from S2-Ar collisions. Broad-band gain is observed on the rare-gas relaxation bands (2,17) (about 475 nm) and (3,18) (480 nm), while absorption is found in the (0,6), (0,7), and (0,8) near-UV (about 360-380-nm) bands where a transient population cascading down the X-state manifold fills the lower levels. It is inferred from the achievement of gain over much of the S2 fluorescence bandwidth that nonselective pumping mechanisms like discharges, solar energy, or flashlamps can be used with S2 as the tunable, chemically stable 'dye'.

Epler, J. E.↗
NASA NTRS1983

An accelerator test of semi-empirical cross-sections

Experimentally measured yields of isotopes of elements from Mg to K resulting from the fragmentation of Ar-40 are compared with calculated yields based on semiempirical cross-section formulas. Excellent mass resolution is obtained in measurements using a beam of 287 MeV/amu Ar-40 incident on a CH2 target. The resolution is made possible by an Si(Li) detector telescope. Whereas the general agreement between calculation and experiment is good, with an rms difference of approximately 24 percent, attention is called to certain significant differences. It is found that important information for refining the semiempirical calculation of fragmentation cross sections can be obtained from data collected during the calibration of cosmic ray detector systems when such calibrations are performed under suitable conditions.

Lau, K. H.↗
NASA NTRS1984

A radiatively pumped CW CO2 laser

A proof of principle experiment to demonstrate the physics of a radiatively pumped laser has been carried out. For the first time, a blackbody cavity has optically pumped a CW CO2 laser. Results are presented from a series of experiments using mixtures of CO2, He, and Ar in which maximum output power was obtained with a 20 percent CO2-15 percent He-65 percent Ar mixture. The dependence of the output power on the blackbody temperature and the cooling gas flow rate is also discussed. By appropriately varying these parameters, continuous output powers of 8-10 mW have been achieved.

Insuik, R. J.↗
NASA NTRS1984

A redetermination of the succinonitrile-water phase diagram

The phase diagram of the water/succinonitrile system often used in modeling binary metallic alloys is determined experimentally using a laser scattering method. Triply distilled and zone-refined succinonitrile is placed in a jacketed water-cooled vessel with a magnetic mixer and a copper-constantan thermocouple, and the melting point is determined under vacuum and under Ar by observing the response of a photodiode placed opposite a laser source as the chamber is cooled and reheated. Then water is added, and the eutectic and monotectic temperatures and the entire phase diagram are determined under Ar. The results are presented in a table and graph and compared to those of Schreinemakers (1897): significant discrepancies are noted and attributed to impurities in the succinonitrile used by Schreinemakers. The importance of accurate phase diagrams for modeling binary alloys is stressed.

Smith, J. E., Jr.↗
NASA NTRS1984

Rare gases in cyclosilicates and cogenetic minerals

The cyclosilicate minerals, beryl, tourmaline, and cordierite, typically contain large amounts of He-4 and Ar-40 which are not in situ radiogenic products. In the study of excess rare gases in cyclosilicates, one of the most enigmatic observations is the age effect, a qualitative tendency for geologically older samples to contain more excess He-4 and Ar-40 than younger samples. The present investigation is concerned with measurements regarding the abundance and isotopic composition of all five rare gases in a number of cyclosilicates as well as in their cogenetic minerals. The significance of the obtained data is discussed. The data indicate that cyclosilicates sample the rare gases present in the environment in which they crystallize. This 'sampling' involves major elemental fractionations which are variable but mineral specific. Cyclosilicates can, therefore, be used to probe the isotopic ratios and elemental compositions.

Saito, K.↗
NASA NTRS1984

Where is the Earth's missing xenon?

Highly volatile elements (e.g., T1, Pb, B, C1, Br, etc.) in the Earth's crust occur in C-chondrite proportions, and so do the atmospheric noble gases Ne, Ar, and Kr. This has led to the suggestion that the Earth acquired its volatiles from a late veneer of C-chondrite-like material. A glaring exception is Xe, which is depleted approx. 20x relative to Ne, Ar, Kr. Three explanations are discussed for the depletion: (1) Xe is preferentially trapped in the crust, either in sediments (3) or in Antarctic ice (4); (2) the Earth's noble gas inventory is non-chondritic (5); or (3) Xe is incompletely outgassed from the mantle.

Wacker, J. F.↗