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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 73 records · Page 4
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NASA NTRS2004

Oxygen Isotopes in Early Solar System Materials: A Perspective Based on Microbeam Analyses of Chondrules from CV Carbonaceous Chondrites

Some of the biggest challenges to understanding the early history of the solar system include determining the distribution of oxygen isotopes amongst materials that existed in the solar nebula, and interpreting the processes that might have resulted in the observed isotopic distributions. Oxygen isotope ratios in any individual mineral grain from a chondritic meteorite may be the cumulative product of a variety of processes, including stellar nucleosynthetic events, gas/solid interactions in the molecular cloud, mixing of independent isotopic reservoirs in the nebula, mass-independent processing in the nebula, and mass-dependent fractionation effects in various environments. It is not possible to unravel this complex isotopic record unless the distribution of oxygen isotope ratios in chondritic materials is fully understood.

Jones, R. H.↗
NASA NTRS1987

Helium isotopic variability within single diamonds from the Orapa kimberlite pipe

The possible relationships between diamond mineralogy and helium isotopes were investigated by measuring the distribution and isotopic composition of He in a suite of well-characterized one-carat diamonds from the Orapa kimberlite, Botswana. The results of crushing in vacuo experiments indicated that most of He was contained in the matrix, rather than in the inclusions of the diamonds. Step-heating of individual diamonds at 2000 C released He of He-3/He-4 ratios that differed by up to a factor of 100 among the two heating steps, revealing large isotopic variations within individual diamonds. It is suggested that this internal isotopic variability is the result of stepwise graphitization: the first heating step initiates graphitization which nucleates around defects in a diamond, and the second step graphitizes the relatively defect-free regions of the diamond. This explanation predicts that the highest He-3/He-4 ratios should be found in most perfect crystals.

Kurz, Mark D.↗
NASA NTRS1975

Three-dimensional imaging of the myocardium with isotopes

Three methods of imaging the three-dimensional distribution of isotopes in the myocardium are discussed. Three-dimensional imaging was examined using multiple Anger-camera views. Longitudinal tomographic images with compensation for blurring were studied. Transverse-section reconstruction using coincidence detection of annihilation gammas from positron emitting isotopes was investigated.

Budinger, T. F.↗
NASA NTRS2024

Genetic Relationships and the Nucleosynthetic Heritage of the Asteroid Bennu

The OSIRIS-REx sample return mission visited the B-type asteroid Bennu and delivered 121.6 gof pristine material to Earth in September 2023. Genetic links between this pristine material and different meteorite groups can be determined using nucleosynthetic isotope variations. These variations reflect the heterogeneous distribution of isotopically distinct dust from different stellar environments within the protoplanetary disk. They can therefore be used to constrain different formation locations of parent asteroids [e.g., 1]. In addition, isotope variations are powerful tracers to establish the nucleosynthetic heritage of returned samples [e.g., 2] and to evaluate mixing and reservoir formation within the disk. Here we present nucleosynthetic Ti and Fe isotope data for samples from Bennu and several carbonaceous chondrites. We also report the Ti isotope composition of hand-picked matrix fractions from CR and CV meteorites.

M Rüfenacht↗
NASA NTRS1986

Element distribution and noble gas isotopic abundances in lunar meteorite Allan Hills A81005

Antarctic meteorite ALLAN HILLS A81005, an anorthositic breccia, is recognized to be of lunar origin. The noble gases in this meteorite were analyzed and found to be solar-wind implanted gases, whose absolute and relative concentrations are quite similar to those in lunar regolith samples. A sample of this meteorite was obtained for the analysis of the noble gas isotopes, including Kr(81), and for the determination of the elemental abundances. In order to better determine the volume derived from the surface correlated gases, grain size fractions were prepared. The results of the instrumental measurements of the gamma radiation are listed. From the amounts of cosmic ray produced noble gases and respective production rates, the lunar surface residence times were calculated. It was concluded that the lunar surface time is about half a billion years.

Kraehenbuehl, U.↗
NASA NTRS2001

The Effect of Stochastic Perturbation of Fuel Distribution on the Criticality of a One Speed Reactor and the Development of Multi-Material Multinomial Line Statistics

The effect of random fuel redistribution on the eigenvalue of a one-speed reactor is investigated. An ensemble of such reactors that are identical to a homogeneous reference critical reactor except for the fissile isotope density distribution is constructed such that it meets a set of well-posed redistribution requirements. The average eigenvalue, , is evaluated when the total fissile loading per ensemble element, or realization, is conserved. The perturbation is proven to increase the reactor criticality on average when it is uniformly distributed. The various causes of the change in reactivity, and their relative effects are identified and ranked. From this, a path towards identifying the causes. and relative effects of reactivity fluctuations for the energy dependent problem is pointed to. The perturbation method of using multinomial distributions for representing the perturbed reactor is developed. This method has some advantages that can be of use in other stochastic problems. Finally, some of the features of this perturbation problem are related to other techniques that have been used for addressing similar problems.

Jahshan, S. N.↗
NASA NTRS2019

New Insights into the Heterogeneity of the Tagish Lake Meteorite: Soluble Organic Compositions of Variously Altered Specimens

The Tagish Lake carbonaceous chondrite exhibits a unique compositional heterogeneity that may be attributed to varying degrees of aqueous alteration within the parent body asteroid. Previous analyses of soluble organic compounds from four Tagish Lake meteorite specimens (TL5b, TL11h, TL11i, TL11v) identified distinct distributions and isotopic compositions that appeared to be linked to their degree of parent body processing (Herd et al. 2011; Glavin et al. 2012; Hilts et al. 2014). In the present study, we build upon these initial observations and evaluate the molecular distribution of amino acids, aldehydes and ketones, monocarboxylic acids, and aliphatic and aromatic hydrocarbons, including compound‐specific δ13C compositions, for three additional Tagish Lake specimens: TL1, TL4, and TL10a. TL1 contains relatively high abundances of soluble organics and appears to be a moderately altered specimen, similar to the previously analyzed TL5b and TL11h lithologies. In contrast, specimens TL4 and TL10a both contain relatively low abundances of all of the soluble organic compound classes measured, similar to TL11i and TL11v. The organic‐depleted composition of TL4 appears to have resulted from a relatively low degree of parent body aqueous alteration. In the case of TL10a, some unusual properties (e.g., the lack of detection of intrinsic monocarboxylic acids and aliphatic and aromatic hydrocarbons) suggest that it has experienced extensive alteration and/or a distinct organic‐depleted alteration history. Collectively, these varying compositions provide valuable new insights into the relationships between asteroidal aqueous alteration and the synthesis and preservation of soluble organic compounds.

Tagish Lake↗
NASA NTRS1983

The isotopic composition of helium at high rigidities

The isotopic abundance distribution of the cosmic radiation at energies beyond 1 GeV/AMU can at the present time be determined only with the geomagnetic method. A balloon-borne instrument was flown for 12 hours near the geomagnetic equator to measure the relative abundance of the helium isotopes He-3 and He-4 around 12 GV rigidity. The sharp rigidity cut-off at equatorial latitudes permitted separation of the two isotopes using a high-resolution-gas Cerenkov counter. The experiment thus confirms the predicted sharp cut-off at those latitudes and demonstrates the potential for isotopic separation of other elements, once flights of longer duration can be made.

Jordan, S. P.↗
NASA NTRSDate not supplied

The Nucleosynthetic Heritage of Bennu

The OSIRIS-REx mission sampled the B-type asteroid Bennu and delivered 121.6 g of material to Earth in September 2023. Nucleosynthetic isotope variations are powerful tracers that can be used to establish relationships between different meteorite groups and the returned samples. They can also constrain the samples’ nucleosynthetic heritage, as well as mixing and reservoir formation in the protoplanetary disk. Nucleosynthetic variations reflect the heterogeneous distribution of isotopically distinct dust in the disk, and as such, they provide evidence for the formation of meteorite parent bodies from isotopically distinct dust reservoirs. They are thus also a means to identify exogenous clasts in Bennu materials. Here, we report Ti and Fe isotope data obtained from Bennu samples and carbonaceous chondrites. We also present Ti isotope data for hand-picked matrix from CV and CR chondrites. An isotopic dataset was obtained on aggregate sample OREX-803015-100 consisting of particles typically <500 μm; therefore, its composition represents an average for Bennu materials. A 20.66 mg aliquot was dissolved at Washington University, St. Louis. From this, 5 mg was analysed for Ti and Fe isotopes on a NeptunePlus MC-ICPMS at ETH Zurich; data from a separate aliquot, analysed at Lawrence Livermore National Laboratory, are reported in a companion abstract. Our results demonstrate a close relationship of Bennu to CI and Ryugu samples and therefore a formation outside the snowline, as hypothesized by the mission. Furthermore, the 50 Ti data from the CV and CR matrix fall consistently below the CI and Bennu values, indicating the presence of a uniform matrix mixed with ⁓0.1–0.7% of refractory inclusions in CIs and Bennu.

M. Schönbächler↗
NASA NTRS1997

An Assessment of the Regional Distribution of the Oxygen-Isotope Ratio in Northeastern Canada

A compilation of mean values of the oxygen-isotope ratio relative to standard mean ocean Water for 22 sites representative of conditions in north-eastern Canada is complemented with data on mean annual surface temperature, latitude, surface elevation, and mean annual shortest distance to open ocean denoted by the 10% sea-ice concentration boundary. Stepwise regression analysis is used to develop a multivariate model suitable to infer the distribution of 6 1"0 in an area of complex topography and possibly mixed source of advected water vapor. The best model is produced by a run in the backward mode at the 95% confidence level in which only temperature, latitude and distance to the open ocean remain in the model (the correlation coefficient is 0.915, the adjusted coefficient of determination is 0.809, the root mean square residual is 1.62). This model is similar to the best 6180 predictive model derived elsewhere for Greenland, suggesting a common principal source of advected moisture.

Giovinetto, Mario B.↗
NASA NTRS1997

Areal Distribution of the Oxygen-Isotope Ratio in Greenland

Mean values of the oxygen-isotope ratio relative to standard mean ocean water reported for 46 sites on the Greenland ice sheet are compiled together with data on mean annual surface temperature, latitude, 6180 elevation, and mean annual shortest distance to the open ocean denoted by the 10% sea-ice concentration boundary. Stepwise regression analyses, with 6180 as the dependent variable, define two robust models. In the forward mode at the 99.9% confidence level, only temperature enters the model. In the backward mode at the 95% confidence level, only temperature, latitude, and distance to the open ocean remain in the model. Inversions of the models on the basis of 160 gridpoint locations 100 km apart in the area delimited by the surface equilibrium line produce four contoured distributions of 6"0. Two distributions are based on the bivariate model and two on the multivariate model. The second distribution for each model is obtained substituting mean annual surface-temperature values obtained from the Nimbus-7 Temperature Humidity Infrared Radiometer (THIR) database. All four distributions are considered valid, and differences between them are evaluated using contoured anomaly maps. It is suggested that the inversion of the multivariate model using THIR data provides the more reliable pattern for studies of atmospheric advection or for the derivation of ice-flow adjustments for 6180 series obtained from deep-core or ablation-zone sites.

Zwally, H. Jay↗
NASA NTRS1972

Hydrogen formation in the photolysis of propyne at 1236 A.

A Kr resonance lamp was used in the investigations. All experiments were performed at 25 C and 0.2 torr of propyne. Between 5% and 25% of the propyne was decomposed in any one experiment. It was found that the addition of 25% C2D4 had no effect on the quantum yield of molecular hydrogen. This suggests that hydrogen formation in the photolysis of propyne at 1236 A occurs exclusively via a molecular process. Pressure effects on the distribution of isotopic hydrogen formed in the photolysis were also investigated.

Payne, W. A.↗
NASA NTRS1981

Lunar volcanic glasses and their constraints on mare petrogenesis

The compositional properties of volcanic glasses from the Apollo 11, 14, 15 and 16 landing sites are examined and implications of the results for mare basalt petrogenesis and deep lunar structures are discussed. Major-element and nickel analyses were performed on the glasses using electron probe techniques, and R-mode principal component analysis was performed on the 19 different compositions of glass distinguished. The glasses are found to form two distinct chemical arrays based on the major elements and Ni. The presence of two chemically isolated cumulate systems in the mantle at different depths is thus inferred, and a model is developed for mare petrogenesis in which each system was itself composed of two lithologic components that underwent hybridization, assimilation or mixing to generate the large compositional range of magmas represented by the lunar volcanic glasses. The surface-correlated elements associated with the volcanic glasses are attributed to another reservoir in the deep interior which may be responsible for gas emissions causing lunar transient phenomena. The model developed allows predictions to be made concerning the liquidus phase relations, trace and radiogenic element distributions, nonradiogenic isotope compositions and sample ages.

Delano, J. W.↗
NASA NTRS1987

Oxygen-18 tracer study of the passive thermal oxidation of silicon

This work focuses on the thermal oxidation of silicon near 1273 K using the double-tracer oxidation method. The results confirm that oxidation occurs by the transport of electrically neutral nonnetwork oxygen through the interstitial space of the vitreous silica (v-SiO2) scale. Simultaneously, self- (or isotopic-) diffusion occurs in the network, resulting in characteristic isotopic fraction distributions near the gas-scale interface. The self-diffusion coefficients calculated from these profiles agree with those reported for tracer diffusion in v-SiO2, and the diffusion coefficient calculated from the scale growth is consistent with reported O2 permeation data. An important parameter that describes the double-oxidation behavior is a ratio relating the scale thickness grown during the second oxidation, the network self-diffusion coefficient for oxygen, and the time of the second oxidation.

Cawley, J. D.↗