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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 55 records · Page 3
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NASA NTRS1980

Endemic isotopic anomalies in titanium

Abundances of the titanium isotopes were determined using a new high-precision technique that shows terrestrial, lunar, and bulk meteorite samples to be indistinguishable. Ca-Al-Ti-rich inclusions in the Allende meteorite are found to contain Ti of widely varying isotopic composition reflecting the presence of at least three nucleosynthetic components. The anomalies in Ti appear to be relatively widespread and, when correlated with Ca data, provide a clue to nucleosynthesis in the neighborhood of the iron peak and to the late-stage nucleosynthetic processes which immediately preceded formation of the solar nebula.

Niederer, F. R.↗
NASA NTRS1977

Isotopic anomalies and proton irradiation in the early solar system

Nuclear cross sections relevant to the various isotopic-abundance anomalies found in solar-system objects are evaluated in an attempt to set constraints on the hypothesized mechanism of irradiation of forming planetesimals by energetic protons from the young sun. A power-law proton spectrum is adopted, attention is restricted to proton energies less than about 20 MeV, and average cross sections are calculated for several reactions that might be expected to lead to the observed anomalies. The following specific anomalies are examined in detail: Al-26, Na-22, Xe-126, I-129, Kr-80, V-50, Nb-92, La-138, Ta-180, Hg-196, K-40, Ar-36, O-17, O-18, N-15, C-13, Li, Be, and B. It is suggested that the picture of presolar-grain carriers accounts for the facts more naturally than do irradiation models.

Clayton, D. D.↗
NASA NTRS1985

Titanium isotopic anomalies in hibonites from the Murchison carbonaceous chondrite

The isotopic compositions of titanium in eight grains of hibonite (CaAl12O19) from the carbonaceous chondrite Murchison have been determined by high precision secondary ion mass spectrometry using an ion microprobe. The titanium in the hibonites varies greatly in Ti-50 from about -42 to +8 permil (relative to terrestrial) with smaller (up to 4 permil), but clearly resolvable, effects in Ti-46 and Ti-48. These results confirm the presence of widespread negative anomalies suggested by the results of Hutcheon et al. (1983) on hibonites from Murchison. The magnitude of these variations seems explicable only in terms of nucleogenic processes which produced extremely variable titanium isotopic abundances in the hibonite source materials. The hibonites evidently did not participate to the same extent as most material in the mixing and homogenisation processes that accompanied the formation and later evolution of the solar system.

Ireland, T.↗
NASA NTRS1997

Sulfur and Hydrogen Isotope Anomalies in Meteorite Sulfonic Acids

Intramolecular carbon, hydrogen, and sulfur isotope ratios were measured on a homologous series of organic sulfonic acids discovered in the Murchison meteorite. Mass-independent sulfur isotope fractionations were observed along with high deuterium/hydrogen ratios. The deuterium enrichments indicate formation of the hydrocarbon portion of these compounds in a low-temperature environment that is consistent with that of interstellar clouds. Sulfur-33 enrichments observed in methanesulfonic acid could have resulted from gas-phase ultraviolet irradiation of a precursor, carbon disulfide. The source of the sulfonic acid precursors may have been the reactive interstellar molecule carbon monosulfide.

Cooper, George W.↗
NASA NTRS1981

Isotopic anomalies in the galactic cosmic-ray source

Observations of the isotopic compositions of oxygen, neon and magnesium nuclei in galactic cosmic rays are presented and discussed in terms of nucleosynthesis at the galactic cosmic ray source. The observations, made with a charged-particle telescope carried aboard ISEE-3, show enhancements in the Ne-22/Ne-20, Mg-25/Mg-24 and Mg-26/Mg-24 ratios with respect to solar system abundances by factors of 4.1, 1.6 and 1.6, respectively. The data thus demonstrate that the galactic cosmic ray source is compositionally distinct from the solar system, and also rule out the models of Woolsey and Weaver (in press) for the synthesis of excess Ne-22 and a model of normal star formation, evolution and mass loss in a region enriched in metals.

Wiedenbeck, M. E.↗
NASA NTRS2003

Endemic Ru Isotopic Anomalies in Iron Meteorites and in Allende

Small variations for Mo isotopes have been observed recently in the Allende meteorite and in iron meteorites, mesosiderites, and pallasites, using ICPMS. Large effects for Mo have been reported for leaches of Orgueil and in SiC and graphite from Murchison. Variations for Mo in bulk Allende and in Murchison have also been presented by NTIMS. Effects in Ru isotopes can define further the preserved exotic r, s, and p contributions in this mass region, and possible effects in Ru-98 and Ru-99 from Tc-98 (4.2 Ma half-life) and Tc-99 (0.21 Ma half-life). Previous attempts at determination of Ru isotopes yielded no resolved effects. The present work represents a substantial improvement in precision over the earlier work. Chemical and mass spectrometric analytical techniques are presented to determine the Ru isotope compositions in terrestrial standards and in meteorites.

Chen, J. H.↗
NASA NTRS1977

A theoretical investigation of isotopic anomalies of xenon in terrestrial and extra-terrestrial samples

The abundance and isotopic composition of noble gases in meteorites is discussed in relation to the composition of the early solar system. Carbonaceous chondrites contain a unique Xenon-X, which is rich in heavy and light isotopes. Variations in the occurrence of type-X and type-Y (the normal component) noble gases are of such magnitude that neither the injection of material from a nearby supernova nor presence of presolar grains can account for the anomalies in meteorites. Therefore, it is suggested that the entire solar system may have condensed from the debris of a single local supernova.

Sabu, D. D.↗
NASA NTRS1993

The astrophysical interpretation of isotope anomalies in graphite and SiC grains of chondrites

The C, N, and Mg isotopic compositions in graphite and SiC grains of carbonaceous chondrites can be explained by nuclear processes in massive O,B stars of second generation passed a stage of WR star with intensive stellar wind, where grain condensation had taken place. The interstellar graphite and SiC grains with anomalous isotopic compositions of C, N, Ne, and Si and other elements of nucleosynthetic origin, found in non-equilibrated chondrites, are most suitable for determination of astro-physical objects, where nucleosynthesis had taken place. Two objects were examined: (1) massive O,B stars of second generation passed a stage of WR star with intensive stellar wind (O,B-WR model) and (2) low-mass stars (1 less than or equal to M/solar mass less than or equal to 3) during thermally pulsing asymptotic giant branch phase (TP-AGB model).

Lavrukhina, A. K.↗
NASA NTRS1972

Search for extinct natural radioactivity of Pb205 via thallium-isotope anomalies in chondrites and lunar soil.

Thallium and Pb204 contents were determined by stable-isotope-dilution analysis in 16 chondrites, one achondrite, and Apollo 11 and 12 lunar fines. Meteoritic thallium contents vary over a large range, 0.02 to 100 ppb, corresponding to the fact that thallium is a highly fractionated volatile element. Lunar thallium contents are less than 5 ppb. The Tl205/Tl203 ratio was determined in most of the samples, with precision ranging from 0.03% to several percent depending mainly on the amount of thallium present. No variations from the terrestrial ratio were observed. The chondritic isochron slope for Pb205 (13.8-m.y. half-life) is less than or equal to 0.00009 (99% confidence level), corresponding to an interval of at least 60 m.y. and possibly exceeding 120 m.y. between the termination of s-process nucleosynthesis and the lead-thallium fractionations.

Huey, J. M.↗
NASA NTRS1974

Theoretical investigation of isotopic anomaly of xenon in carbonaceous chondrites and other terrestrial and extra-terrestrial samples

The composition of Xe released from carbonaceous chondrites between 600 and 1000 C, particularly its isotopic trapped forms, is analyzed. Data show trapped Xe to have the following forms: Xe-124, 126, 130, 131, 132, 134, and 136. Attempts were also made to explain the Xe anomaly by mass fractionation as well as determine the relationship between metoritic trapped Xe and solar Xe.

Sabu, D. D.↗
NASA NTRS1988

Isotopic anomalies of Ne, Xe, and C in meteorites. I - Separation of carriers by density and chemical resistance

The carriers of presolar noble gases were studied by isotopically analyzing 19 separates from the Murray and Murchison C2 chondrites for Ne, Xe, C, and N. It is found that the carriers of Ne-E(H) and Xe-S are resistant to HCl, HF, boiling HClO4, and CrO3-H2SO4, and thus must be either diamond or some resistant carbide or oxide. The carrier of Ne-E(L) may be some form of amorphous carbon with delta C13 of about +340 percent. A new carbon component, C theta, found as 0.2-2-micron inclusions in Murchison spinel, is amorphous and contains little or no noble gas. A new heavy nitrogen component is found which has an abundance of about 1 ppm in the bulk meteorite, combusts at 450-500 C, and may be associated wtih isotopically normal carbon or with C-alpha.

Ming, Tang↗
NASA NTRS1991

Correlated Si isotope anomalies and large C-13 enrichments in a family of exotic SiC grains

A hypothesis is presented to the effect that the distinctive morphological characteristics and comparatively simple Si isotope systematics identify the platy SiC crystals as a genetically related family, formed around a single isotopically heterogeneous presolar star on an association of related stars. The enrichments in C-13 and the Si isotope systematics of the platy SiC are broadly consistent with theoretical models of nucleosynthesis in low-mass, carbon stars on the ASG. The Si isotope array most plausibly reflects mixing between (Si-28)-rich material, inherited from a previous generation of stars, and material enriched in Si-29 and Si-30, produced in intershell regions by neutron capture during He-burning. The absence of a correlation between the Si and C isotopic compositions of the SiC suggests either episodic condensation of SiC, extending over several thermal pulses, in the atmosphere of a single star, or the derivation of the SiC from several stars characterized by different rates of C-13 production.

Stone, J.↗
NASA NTRS1979

Injection of isotopic anomalies into the early solar nebula

The effectiveness of injecting material from outside the solar system into the early solar nebula was studied. Hydrodynamic calculations showed that the conditions of external injection of isotopically anomalous matter resemble a supernova remnant shell impacting an interstellar H I cloud. Since the injection process for grains or gas is determined before the impinging material penetrates a skin layer, the results for an H I edge should be valid for any configuration which joins the interstellar medium with an H I boundary zone. The effects of initial injection velocity, gas cooling, and magnetic fields are considered, and it is shown that grain penetration is limited to a layer with column density on the order of the grain mass/area ratio and that Rayleigh-Taylor instabilities are not expected to be effective at mixing the anomalous matter into the nebula during a cloud/shell interaction.

Margolis, S. H.↗
NASA NTRS1980

Silver isotopic anomalies in iron meteorites - Cosmic-ray production and other possible sources

Sources of excess Ag-107 observed in iron meteorites are investigated with emphasis on reactions of cosmic-ray particles with palladium. Cross sections for the production of the silver isotopes from palladium by energetic cosmic-ray particles are estimated to calculate spallogenic production rates relative to that of Mn-53 from iron. The upper limits for the production rates of Ag-107 and Ag-109 by energetic galactic cosmic-ray particles are 690 and 270 atoms/min/kg(Pd), respectively, and the maximum rate for making excess Ag-107 by spallation reactions is 400 atoms/min/kg(Pd). The excess Ag-107 cannot be produced by a long exposure to cosmic-ray particles, and because it is harder to make the amount of Pd-107 observed in the iron meteorites by an early intense proton irradiation than it is to make the Al-26 observed in other meteorites, it is concluded that the excess Ag-107 is due to the decay of nucleosynthetic Pd-107 in the iron meteorites.

Reedy, R. C.↗
NASA NTRS1978

Condensation in supernova ejecta and isotopic anomalies in meteorites

An investigation is conducted of the physical and chemical conditions in an expanding supernova envelope, taking into account the likelihood of grain formation and the chemical composition of the grains. An 'onionskin' presupernova model is used to estimate the chemical and isotopic abundance in the various shells of ejected supernova material. Condensation calculations are performed over a range of pressures and chemical compositions for each of these shells in order to determine the type of grains which could be produced in supernova ejecta. Only grains that are stable under the physical conditions encountered in the presolar nebula can survive and retain their anomalous composition. Two regions in the presolar nebula are considered, and the possible surviving grains are deduced from the appropriate condensation sequences.

Lattimer, J. M.↗
NASA NTRS1985

A striking nitrogen isotope anomaly in the Bencubbin and Weatherford meteorites

The stony-iron meteorites Bencubbin and Weatherford contain nitrogen with a ratio of nitrogen-15 to nitrogen-14 larger than normal by as much as a factor of 2. The excess nitrogen-15 may be due either to a nucleosynthetic origin or to extreme isotopic fractionation. In the former case, it may reflect failure to homogenize nitrogen-15 produced in nova explosions. In the latter case, it may reflect chemical processing at temperatures below 40 K in a presolar molecular cloud.

Prombo, C. A.↗
NASA NTRS2005

Nitrogen Isotopic Anomalies in a Hydrous Interplanetary Dust Particle

Interplanetary dust particles (IDPs) collected in the stratosphere are the fine-grained end member (5 - 50 microns in size) of the meteoritic material available for investigation in the laboratory. IDPs are derived from either cometary or asteroidal sources. Some IDPs contain cosmically primitive materials with isotopic signatures reflecting presolar origins. Recent detailed studies using the NanoSIMS have shown there is a wide variation of isotopic signatures within individual IDPs; grains with a presolar signature have been observed surrounded by material with a solar isotopic composition. The majority of IDPs studied have been anhydrous. We report here results from integrated NanoSIMS/FIB/TEM/Synchrotron IR studies of a hydrous IDP, focused on understanding the correlations between the isotopic, mineralogical and chemical compositions of IDPs.

Smith, J. B.↗