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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Noble gases in the Murchison meteorite - Possible relics of s-process nucleosynthesis

The Murchison carbonaceous chondrite contains a new type of xenon component, enriched by up to 50 percent in five of the nine stable xenon isotopes, mass numbers 128 to 132. This component is released at 1200 to 1600 C from a severely etched mineral fraction. Krypton shows a similar but smaller enrichment in the isotopes 80 and 82. Neon and helium released in the same interval also are quite anomalous, being highly enriched in the isotopes 22 and 3. These patterns are strongly suggestive of three nuclear processes believed to take place in red giants: the s process (neutron capture on a slow time scale), helium burning, and hydrogen shell burning. If this interpretation is correct, then primitive meteorites contain yet another kind of alien, presolar material: dust grains ejected from red giants.

Srinivasan, B.↗
NASA NTRS1978

Comparisons between observed and predicted cosmogenic noble gases in lunar samples

Comparisons are made between cosmogenic production rates and isotopic ratios predicted on the basis of nuclear systematics with those observed in well-documented lunar samples. Although some significant differences are found, the agreement in general is surprisingly good. The predicted production rates for Ar-38 and Xe-126 agree reasonably well with observation but the predicted rate for Ne-21 appears to be too high; in most cases the predicted rate for Kr-83 agrees to within 50%, although some larger differences are apparent. There are some prominent cases in which predicted isotopic compositons differ from observation: Kr-78/Kr-83 trends in the wrong sense with the Zr/Sr ratio; Xe-124/Xe-126 is too large by about 13%; Xe-128/Xe-126 is too small by about 6%; Xe-130/Xe-126 is too low by 30-40%.

Hohenberg, C. M.↗
NASA NTRS1979

Solar and terrestrial noble gases in magnetospheric precipitation

Metal-foil collectors were installed on the external structure of Skylab to entrap precipitating magnetospheric particles. The foils were retrieved, and the entrapped helium, neon, and argon were isotopically analyzed in a high-resolution mass spectrometer. Solar and terrestrial helium and neon and terrestrial argon were detected. As expected, the isotopic composition of neon and argon in the high atmosphere was found to be strongly fractionated. Special techniques were used to estimate the initial particle energy of He-3. The measured He-3 flux is consistent with the assumption that precipitating solar He-3 is the major source of terrestrial He-3.

Lind, D. L.↗
NASA NTRS1980

Isotopic anomalies of noble gases in meteorites and their origins. VI Presolar components in the Murchison C2 chondrite

Rare gases were analyzed by stepped heating in five fractions of a chemically resistant residue from Murchison that had been separated according to grain size and resistance to HClO4. Nine gas components were recognized, of which three appear to be presolar: (1) Ne-E(H) released at 1000-1600 C and located in spinel; (2) Ne-E(L) released at less than 800 C and apparently located in a carbonaceous phase of grain size up to 10 microns; and (3) s-process Xe and Kr released at 1200-1600 C and located in a poorly characterized, possibly carbonaceous phase, distinct from the host phase of Ne-E(L).

Alaerts, L.↗
NASA NTRS1979

Predicted versus observed cosmic-ray-produced noble gases in lunar samples - Improved Kr production ratios

New sets of cross sections for the production of krypton isotopes from targets of Rb, Sr, Y, and Zr have been constructed primarily on the bases of experimental excitation functions for Kr production from Y. These cross sections were used to calculate galactic-cosmic-ray and solar-proton production rates for Kr isotopes in the moon. The paper reports spallation Kr data obtained from ilmenite separates of rocks 10017 and 10047. Production rates and isotopic ratios for cosmogenic Kr observed in ten well-documented lunar samples and in ilmenite separates and bulk samples from several lunar rocks with long but unknown irradiation histories were compared with predicted rates and ratios. The agreements were generally quite good.

Regnier, S.↗
NASA NTRS1986

Shock-implanted noble gases - An experimental study with implications for the origin of Martian gases in shergottite meteorites

The shock-implantation of gases is studied by artificially shocking whole rock and power samples of terrestrial basalt to pressures of 2-40 GPa. Ar, Kr, Xe, and Ne were implanted into the silicate. It is observed that the amount of implanted gas is linearly proportional to its partial pressure over a pressure range of 0.0001 to 0.1 atmosphere. The fractionation effect in the implanted gas and the gas diffusion properties are examined. The amounts of gas that would have been implanted with 100 percent efficiency are calculated from the measured porosities of the power samples and are compared to observed abundances. It is determined that the implantation efficiencies are approximately 0.5 percent at 2 GPa, 7 percent at 5 GPa, and greater than 50 percent at both 20 and 35 GPa. The experimental data correlate with the shock implantation of Martian gases without mass fractionation into the shock-melted phase of meteorite EETA 79001.

Bogard, Donald D.↗
NASA NTRS1988

Non-atmospheric noble gases from CO(sub 2) well ga

In recent years a number of studies of both terrestrial and extraterrestrial material has allowed the piecing together of a picture of events occurring in the early solar system (4.5 Gyr ago), including the formation of the earth. However, before this picture can be completed with an appropriate amount of detail it will be necessary to make further advances. One of the areas where knowledge is lacking is the chemical and isotopic composition of the earth as a whole. The lack of knowledge has less to do with the capabilities of modern techniques than with the availability of samples to study. About 99.6 percent of the earth's mass is contained in the mantle and core, leaving less that 1 percent in the crust and atmosphere. Although the crust is derived from the mantle it has undergone extensive changes and it is therefore difficult (although not impossible) to use crustal material to study events occurring 4.5 Gyr ago. More information about the early earth could be obtained from studies of the mantle but it is difficult to obtain mantle material, because the mean thickness of the crust is 17 km, much greater than even the deepest mines or drill shafts. The two types of available mantle samples are discussed.

Caffee, M. W.↗
NASA NTRS1988

Noble gases, C,N, and Si isotopes in interstellar SiC form the Murchison carbonaceous chondrite

Isotopic measurements of presolar interstellar silicon carbide are presented. Silicon carbide was recently identified in a primitive meteorite Murray. There exists strong evidence that the silicon carbide predates the formation of the solar system and originated in the atmospheres of certain stars. Thus, this material provides a link with its stellar sources and gives the opportunity to study processes taking place in distant stars.

Ming, Tang↗
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

Tectonic implications of radiogenic noble gases in planetary atmospheres

An account is given of the ways in which the He-4 and Ar-40 radiogenic isotopes furnish important constraints on planetary interior tectonics. In the case of the earth, where there are such independent constraints on radiogenic isotope concentrations as observed surface heat flow, the specification of radiogenic isotope concentration allows the interpretation of data on the Ar-40 atmospheric mass and mantle He-4 in terms of models for the entire mantle and of layered mantle convection. He loss rate estimates through the Venus atmosphere indicate a flux that is nearly equal to that through the earth atmosphere.

Turcotte, D. L.↗