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Results for “Isotopic composition”

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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Nitrogen abundances and isotopic compositions in stony meteorites

Nitrogen contents range from a few parts per million in ordinary chondrites and achondrites to several hundred parts per million in enstatite chondrites and carbonaceous chondrites. Four major isotopic groups are recognized: (1) C1 and C2 carbonaceous chondrites, (2) enstatite chondrites, (3) C3 chondrites, and (4) ordinary chondrites. The major variations are primary, representing isotopic abundances established at the time of condensation and accretion. Secondary processes, such as spallation reactions, solar wind implantation and metamorphic loss may cause small but observable isotopic variations in particular cases. The large isotopic difference between enstatite chondrites and carbonaceous chondrites cannot be accounted for by equilibrium condensation from a homogeneous nebular gas, and requires either unusually large kinetic effects, or a temporal or spatial variation of isotopic composition of the nebula. Nitrogen isotopic heterogeneity in the nebula due to nuclear processes has not been firmly established, but may be required to account for the large variations found within the Allende and Leoville meteorites. The unique carbonaceous chondrite, Renazzo, also requires a special source. It is not yet possible, from the meteoritic data, to establish the mode of accretion of nitrogen onto the primitive earth.

Kung, C.-C.↗
NASA NTRS1975

A Cerenkov-Range analysis of the isotopic composition of cosmic rays with Z from 6 to 26

High-altitude balloon data on the isotopic composition of heavy cosmic rays are reported. The experiment used a Cerenkov detector, arrays of scintillators, and a digitized wire spark chamber. Peaks assigned to the mono-isotopic elements F and Na indicate that an absolute mass scale can be derived from the data. Even-Z elements in the Z range from 12 through 16 are represented mainly by alpha-particle nuclei. Neutron-rich components dominate in the case of neon present. Mass histograms are plotted for C, O, N, Ne, Mg, and Fe.

Fisher, A. J.↗
NASA NTRS1986

Isotopic compositions of bismuth, lead, thallium, and mercury from mini r-processing

The yields of stable isotopes of Bi, Pb, Tl and Hg as well as yields of Pb-205 are calculated with a parametrized model for 'mini r-processing' in the Ne, O, C-rich zones of explosive burning in massive stars. The Pb isotopic compositions stand out by their comparatively low Pb-207 yields and by the fact that this r-process variant yields Pb-204 quite abundantly. The average Pb-205/Pb-204 yield ratio of 6.1 is the same order of magnitude as yield ratios deduced for s-processing. The Hg from this mini r-process looks like normal solar-system mercury, but with Hg-196 missing and the light s-isotopes A = 198, 199, 200 and 201 depleted (especially the odd-A species).

Heymann, D.↗
NASA NTRS2018

A Submm-Wave Comet Explorer for Water Isotopic Composition Measurements

Remote submm-wave spectrometers have the capability of providing statistically significant numbers of isotopic composition measurements within the budget constraints of available planetary missions. This talk will present a mission and instrument concept that would enable an accurate measurement of the D/H ratio on not one but several dozens of comets in a four-year mission lifetime. The instrument would utilize advanced cryogenic detectors that would allow us to measure the abundance of the para and ortho spin states of water and its isotopologues. State of the art superconducting heterodyne receivers have been developed that provide detection sensitivities approaching the quantum limit in the 500 GHz frequency range enabling the measurement of D/H ratio on around 50 comets from an observatory stationed for example at the thermally benign Lagrange point L2.

Feldman, Sabrina↗
DOE OSTI2022

The NEON Daily Isotopic Composition of Environmental Exchanges Dataset

The National Ecological Observatory Network (NEON) provides open-access measurements of stable isotope ratios in atmospheric water vapor (δ 2 H, δ 18 O) and carbon dioxide (δ 13 C) at different tower heights, as well as aggregated biweekly precipitation samples (δ 2 H, δ 18 O) across the United States. These measurements were used to create the NEON Daily Isotopic Composition of Environmental Exchanges (NEON-DICEE) dataset estimating precipitation (P; δ 2 H, δ 18 O), evapotranspiration (ET; δ 2 H, δ 18 O), and net ecosystem exchange (NEE; δ 13 C) isotope ratios. Statistically downscaled precipitation datasets were generated to be consistent with the estimated covariance between isotope ratios and precipitation amounts at daily time scales. Isotope ratios in ET and NEE fluxes were estimated using a mixing-model approach with calibrated NEON tower measurements. NEON-DICEE is publicly available on HydroShare and can be reproduced or modified to fit user specific applications or include additional NEON data records as they become available. The NEON-DICEE dataset can facilitate understanding of terrestrial ecosystem processes through their incorporation into environmental investigations that require daily δ 2 H, δ 18 O, and δ 13 C flux data.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1993

s-process Ba isotopic compositions in presolar SiC from the Murchison meteorite

We have measured, by thermal ionization mass spectrometry, the isotopic composition of Ba in interstellar SiC-enriched samples (the KJ series) prepared from the Murchison meteorite. Ba in these samples is strongly enriched in components plausibly understood as s-process nucleosynthetic products. Inferred s-process compositions are different from the average s-process contribution to solar system materials in the sense of indicating lower effective neutron exposure. There are variations in s-process compositions which correlate with grain size, indicating lower neutron exposure for the larger grains. The inferred s-process compositions differ significantly from previous theoretical predictions, indicating the need for revision of relevant neutron capture cross sections and providing a target for more detailed modeling of s-process nucleosynthesis in specific stellar environments.

Prombo, C. A.↗
NASA NTRS1982

The charge and isotopic composition of Z = 6-14 cosmic ray nuclei at their source

Using data from a cosmic ray charge-isotope telescope flown on balloons, both the charge and isotopic composition are determined of Z = 6-14 cosmic ray nuclei. A low abundance for the elements N and Ne in the cosmic ray source relative to solar cosmic rays is observed. For the isotopes, a cosmic ray source ratio Ne-22/Ne-20 is found that is 3.52 plus or minus 0.67 times the solar ratio, this enhancement being due in part to an enhancement of Ne-22 and in part to an underabundance of Ne-20. Also observed are possible enhancements of the Mg-26/Mg-24 ratio, which is 1.40 plus or minus 0.24 times the solar t ratio, and the C-13/C-12 ratio, which is 2.90 plus or minus 0.93 times the solar ratio. For Ne, the underabundance of this element, coupled with the overabundnace of the isotope Ne-22, is seen as providing an important new clue to the nucleosynthesis processes producing these differences.

Webber, W. R.↗
DOE OSTI2020

Carbon Isotope Composition and the NDVI as Phenotyping Approaches for Drought Adaptation in Durum Wheat: Beyond Trait Selection

High-throughput phenotyping platforms provide valuable opportunities to investigate biomass and drought-adaptive traits. We explored the capacity of traits associated with drought adaptation such as aerial measurements of the Normalized Difference Vegetation Index (NDVI) and carbon isotope composition (δ13C) determined at the leaf level to predict genetic variation in biomass. A panel of 248 elite durum wheat accessions was grown at the Maricopa Phenotyping platform (US) under well-watered conditions until anthesis, and then irrigation was stopped and plot biomass was harvested about three weeks later. Globally, the δ13C values increased from the first to the second sampling date, in keeping with the imposition of progressive water stress. Additionally, δ13C was negatively correlated with final biomass, and the correlation increased at the second sampling, suggesting that accessions with lower water-use efficiency maintained better water status and, thus, performed better. Flowering time affected NDVI predictions of biomass, revealing the importance of developmental stage when measuring the NDVI and the effect that phenology has on its accuracy when monitoring genotypic adaptation to specific environments. The results indicate that in addition to choosing the optimal phenotypic traits, the time at which they are assessed, and avoiding a wide genotypic range in phenology is crucial.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1977

The relation between isotopic composition of argon and carbon in natural gases

The methods and results of determination of the argon and carbon isotope compositions of hydrocarbon gases of Mezozoic complexes of Western Siberia are presented. Based on the Ar-36, Ar-40, C-12, C-13 content of the various deposits and on the presumed mechanisms of entry of these isotopes into the deposits, it is concluded that formation of natural gas in some deposits included vertical migration from a lower complex.

Gavrilov, Y. Y.↗
NASA NTRS1980

A measurement of the isotopic composition of galactic cosmic ray carbon, nitrogen and oxygen

The paper reports the results of an investigation of the isotopic composition of galactic cosmic ray carbon, nitrogen and oxygen (80-230 MeV/amu) made using the U.C. Berkeley HKH instrument aboard the ISEE-3 spacecraft. The combination of high mass resolution and a large statistical sample makes possible a precise determination of the relative isotopic abundances for these elements. In local interplanetary space the following values are found: C-13/C = 0.067 + or - 0.008, N-15/N = 0.54 + or - 0.03, O-17/O less than 0.027, and O-18/O - 0.019 + or - 0.003.

Wiedenbeck, M. E.↗
NASA NTRS1974

Isotopic composition of cosmic ray nuclei with Z greater than or equal to 10

Results of measurements of the isotopic composition of Z greater than or equal to 10 cosmic ray nuclei using a new technique employing a combination of Cerenkov and total energy counters. An effective mass resolution of about 0.4 AMU is obtained for particles with energies between 400 and 500 MeV/nuc and charges between 12 and 16. The preliminary mass distribution of nuclei with charges from 12 to 28 is presented and discussed.

Webber, W. R.↗
NASA NTRS1990

The isotopic composition of Ag in meteorites and the presence of Pd-107 in protoplanets

Results are presented on the isotopic composition of Ag and the concentrations of Pd and Ag in metal and sulfide phases in iron meteorites Gibeon, Derrick Peak, and Mundrabilla and in schereibersite in Derrick Peak. It was found that almost all iron meteorite samples with a ratio of Pd-108/Ag-109 greater than about 400 had an excess of Ag-107. The results, in conjunction with the data of Chen and Wasserburg (1983) on IIIA-IIIB meteorites, demonstrate the widespread occurrence of excess Ag-107 in diverse types of small early planetary bodies. The excess Ag-107 is believed to be produced by the decay of Pd-107.

Chen, J. H.↗