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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Calcium isotopic anomalies and the lack of aluminum-26 in an unusual Allende inclusion

This letter reports the discovery of an unusual Allende inclusion that is rich in hibonite, Ca(Al, Ti, Mg)12O19, the most refractory and possibly the most primitive major oxide mineral from the solar nebula. The Mg and Ca isotopic compositions of this hibonite-rich inclusion are studied in order to investigate the distribution of Al-26 in the solar system and to extend the search for isotopic anomalies. The Mg results indicate that no Mg isotopic anomalies are present, that the initial Al-26/Al-27 ratio for the inclusion when it crystallized was less than 200 billionths, and that the Mg mass-fractionation effect in the inclusion must be less than about 20 per mil/amu for the hibonite and 10 per mil/amu for other phases. The Ca studies reveal that large Ca mass-fractionation effects of about 7.5 per mil/amu are present and that additional small 'nonlinear' effects of presumably nuclear origin at a level of about 1 to 2 per mil are present in at least Ca-42. A plausible model for the evolution of the hibonite-rich inclusion is outlined.

Lee, T.↗
NASA NTRS1990

Monodeuterated methane in the outer solar system. IV - Its detection and abundance on Neptune

The 3nu2 band of CH3D was detected in the spectrum of Neptune near 1.6 micron recorded at a spectral resolution of 4/cm with the Cassegrain Fourier Transportation Spectrometer at the 3.6 m Canada-France-Hawaii Telescope CFHT) on Mauna Kea. The analysis of this spectrum, using spectral synthesis techniques, yielded a CH3D/CH4 ratio of about 0.0006, which corresponds to a global D/H ratio for Neptune of about 0.00012, if CH3D is in isotopic fractionation equilibrium with HD. This value is about an order of magnitude larger than an earlier estimate by Orton et al. (1987) based on deconvolution measurements of unresolved molecular emission in the 8-10-micron region. Comparison of this new determination with previous studies of CH3D in the outer solar system shows that, as in the case of Uranus, the D/H on Neptune is strongly enhanced over that found on Jupiter and Saturn and is comparable to the D/H in methane on Titan and in terrestrial methane and water.

De Bergh, C.↗
NASA NTRS1998

Deuterated Water in Comet C/1996 B2 (Hyakutake) and its Implications for the Origin of Comets

The close approach to the Earth of comet C/1996 B2 (Hyakutake) in March 1996 allowed searches for minor volatile species outgassing from the nucleus. We report the detection of deuterated water (HDO) through its 1(sub 01)-0(sub 00) rotational transition at 464.925 GHz using the Caltech Submillimeter Observatory. We also present negative results of a sensitive research for the J(5-4) line of deuterated hydrogen cyanide (DCN) at 362.046 GHz. Simultaneous observations of two rotational lines of methanol together with HDO in the same spectrum allow us to determine the average gas temperature within the telescope beam to be 69 +/- 10 K. We are thus able to constrain the excitation conditions in the inner coma and determine reliably the HDO production rate as (1.20 +/- 0.28) x 10(exp 26)/s on March 23-24, 1996. Available IR, UV and radio measurements lead to a water production rate of (2.1 +/- 0.5) x 10(exp 29)/s at the time of our HDO observations. The resulting D/H ratio in cometary water is thus (29 +/- 10) x 10(exp -5) in good agreement with the values of (30.8(sub - 5.3, sup +3.8) (Balsiger et al. 1995) and (31.6 +/- 3.4) x 10(exp -5) (Eberhardt et al. 1995) determined in comet P/Halley from in situ ion mass spectra. The inferred 3 a upper limit for the D/H ratio in HCN is 1%. Deuterium abundance is a key parameter for studying the origin and the early evolution of the Solar System and of its individual bodies. Our HDO measurement confirms that, in cometary water, deuterium is enriched by a factor of at least 10 relative to the protosolar ratio, namely the D/H ratio in H2 in the primitive Solar Nebula which formed from the collapse of the protosolar cloud. This indicates that cometary water has preserved a major part of the high D/H ratio acquired in this protosolar cloud through ion-molecule isotopic exchanges or grain-surface reactions and was not re-equilibrated with H2 in the Solar Nebula. Scenarios of formation of comets consistent with these results are discussed.

Bockelee-Morvan, D.↗
DOE OSTI2024

Detection of Isotopes in Urban Source Search Gamma Spectra Using Hopfield Neural Network

Source search campaigns involve the measurement of consecutive background gamma-ray spectra obtained with a mobile detector-spectrometer, such as tellurium-doped sodium iodide NaI(Tl) scintillator detector-spectrometer. Counts are measured with NaI(Tl) detector in short acquisition intervals, such as one second. Detection of isotopes in search data is challenging because of the low signal-to-noise ratio (S/N) of the spectral lines and highly varying background due to naturally occurring radioactive material (NORM). In this work, we investigate the performance of the detection of orphan Cs-137, Am-241, and I-131 isotopes in a gamma ray data set obtained in a search survey. Isotopic detection is performed with a Hopfield Neural Network (HNN), which implements an auto-associative memory by matching incoming measurements to the closest one of its memory-stored signature patterns. HNN is trained on examples of spectra of calibrated isotopic sources with well-resolved spectral lines. During testing, HNN processes spectra with partially complete or distorted isotopic lines. The performance of the HNN detection algorithm is benchmarked with Precision, Recall, and F1 scores. Test results demonstrate the potential of HNN to detect the isotope of interest with high accuracy (F1 > 90%) for all isotopes in this study.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1994

D/H ratios and H2O contents of mantle-derived amphibole megacrysts from Dish Hill, California

D/H ratios are, in principle, useful in characterizing reservoirs of mantle hydrogen and as tracers of volatile transfer processes in Earth's interior. In practice, however, interpretation of isotopic measurements on mantle derived H is complicated by surface processes such as contamination and degassing which may alter the primary D/H ratio. Although there are indications that water associated with subduction zones and certain chemically enriched basalts is enriched in D relative to 'typical' upper mantle water, the extent of isotopic heterogeneity of mantle H remains uncertain. Kaersutitic amphibole megacrysts in alkaline basalts are one of the most widespread sources of mantle water and are therefore potentially useful for large-scale regional studies of D/H variation. However, D/H ratios of these amphiboles vary widely (from plus 8 to minus 113 percent), even in samples from the same locality, so that this potential has yet to be realized. In order to investigate the origin of this variability, and to explore the possibility that primary mantle D/H ratios may be deduced from these amphiboles, we analyzed the D/H ratios and chemical compositions of a suite of 17 kaersutitic amphiboles from Dish Hill, California. This work contrasts with previous studies in which sampling is widespread, but representatives from any given locality are few. Samples were collected from a restricted area on the southern flank of the volcanic center and are associated with the basal volcanic breccia. Fourteen of the samples were large single crystals or crystal fragments (megacrysts, 0.4 to 30 grams), believed to derive from pegmatitic veins crystallized from melts in the mantle. Two were coarse-grained intergrowths of amphibole with olivine and spinel, and one was a thin (2 mm) selvage on a peridotite xenolith.

Bell, David R.↗
NASA NTRS2012

Additional Sr Isotopic Heterogeneity in Zagami Olivine-Rich Lithology

Prior isotopic analyses of Zagami have established differing initial Sr-87/Sr-86 (ISr) ratios of among Zagami lithologies, fine-grained (FG), coarse-grained (CG), and dark mottled lithologies (DML)]. The Zagami sample (KPM-NLH000057) newly allocated from the Kanagawa Prefectural Museum of Natural History contained DML and the Ol-rich lithology which included more ferroan olivines (Ol-rich: Fa(sub 97- 99) vs late-stage melt pockets: Fa(sub 90-97)]). We have combined mineralogy-petrology and Rb-Sr isotopic studies on the Kanagawa Zagami sample, which will provide additional clues to the genesis of enriched shergottites and to the evolution of Martian crust and mantle

Misawa, K.↗
DOE OSTI2022

A window into atmospheric escape on early Mars provided by argon isotopes in a Martian meteorite

Novel analytical approaches to determining the trapped 38 Ar/ 36 Ar ratio of gases contained within Martian meteorites are presented and applied to the Martian regolith breccia Northwest Africa (NWA) 7034 and paired stone NWA 11220. The resulting data indicate that extensive mass-dependent fractionation of atmospheric Ar may have occurred within 150 million years of planetary formation, ostensibly as a result of diffusion-limited hydrodynamic escape. The inferred fractional loss of Ar and lighter atmospheric constituents exceeds 50%. In conclusion, these data suggest that volatiles derived from planetary outgassing and/or impactors may dominate the present abundance of atmospheric Ar.

07 ISOTOPE AND RADIATION SOURCES↗
NASA NTRS1989

Branching ratios in the N + CH3 reaction - Formation of the methylene amidogen (H2CN) radical

The discharge-flow mass spectrometer system described by Brunning and Stief (1986) and Nejad et al. (1988) is used to determine the branching ratios for the reaction N + CH3. The results are presented in extensive tables and graphs and characterized in detail, and the implications for HCN formation in the atmosphere of Titan are considered. It is found that the main reaction channel at room temperature is H2CN + H, with about 10 percent giving HCN + H2; no isotope effects are seen when CH3 is replaced with CD3, and the branching ratios appear to be temperature-independent.

Marston, G.↗
NASA NTRS1991

Chondrite chronology by initial Sr-87/Sr-86 in phosphates?

New data are presented on Rb-Sr isotope analyses of phosphates from nine ordinary chondrites, including accurate identification of initial Sr-87/Sr-86. The initial Sr-87/Sr-86 ratios found in this study were generally significantly higher than the more primitive initial Sr-87/Sr-86 ratios inferred for carbonaceous chondrite refractory inclusions, basaltic achondrites, or bulk ordinary chondrites. Such elevation of initial Sr-87/Sr-86 is generally considered to reflect isotopic redistribution during metamorphism. However, in this study, no evident correlation was found between the phosphate initial Sr-87/Sr-86 compositions and the metamorphic grade. Two possible alternative hypotheses for high initial Sr-87/Sr-86 ratios are considered.

Podosek, Frank A.↗
DOE OSTI2025

Mineralogical and isotopic constraints on early, high-temperature events and reservoirs recorded in the interior of a Type B Ca-Al-rich inclusion from the reduced CV3 chondrite Vigarano

A coordinated mineralogical and oxygen and Al-Mg isotopic study of a Type B Ca-Al-rich inclusion (CAI) from the reduced CV3 chondrite Vigarano was carried out using electron microprobe analysis, transmission electron microscopy, and secondary ion mass spectrometry. This CAI, a once molten igneous object, shows heterogeneous oxygen isotopic compositions among its constituent mineral phases. Spinel is uniformly 16 O-rich with Δ 17 O ≤ −23 ‰. The Δ 17 O values of Al,Ti-diopside in the CAI core range from −11 ‰ to −18 ‰, which are positively correlated with its TiO 2 contents, whereas diopside in the Wark–Lovering (WL) rim is 16 O-rich with Δ 17 O = −23 ‰. Melilite in the CAI mantle shows Δ 17 O values ≤ −10 ‰ only when Åk <15 but becomes more 16 O-poor (Δ 17 O = −3 ‰ to −9 ‰) when Åk >15 . These correlated chemical and oxygen isotopic variations were likely established during crystallization of melilite and Al,Ti-diopside from a partial melt, while spinel preserves the original 16 O-rich composition of the CAI precursor. We infer that a partial melt was isotopically evolving from 16 O-rich to 16 O-poor during melilite crystallization, then back to 16 O-rich during Al,Ti-diopside crystallization via exchange with different gas reservoirs of 16 O-poor and 16 O-rich compositions during heating event(s). Our Al-Mg isotopic measurements of the CAI core and mantle define a single isochron with an inferred initial 26 Al/ 27 Al ratio of (4.93 ± 0.18) × 10 −5 , indistinguishable from that of the WL rim. This indicates that multiple high-temperature events and oxygen isotope exchange with isotopically distinct gas reservoirs occurred rapidly during the CAI formation.

Al-Mg isotopic systematic↗
DOE OSTI2022

E-Area Low Level Waste Generator Inventory Uncertainty Estimation

This report describes the method used to estimate the uncertainty and bias in the low-level waste inventory, as reported by Waste Generators, for waste disposed in the E-Area Low-Level Waste Facility at SRS. The waste cut uncertainty and bias is summed to calculate the current total uncertainty and bias in each disposal unit in the E-Area Low-Level Waste Facility. This information is used to estimate the future uncertainty and bias when all disposal units are closed. For most waste cuts, there are two areas of inventory uncertainty and bias: in the isotopic characterization of the waste stream and in the measurement of total waste cut activity. Waste stream characterization is accomplished through a combination of process knowledge and analytical measurements. This characterization is documented by a technical baseline that describes the relative quantity of each isotope present in the waste stream. The total activity of each individual waste cut is usually measured directly or is calculated through a ratio of activity per weight or activity per volume. The waste cut total activity is multiplied by the waste stream isotopic fraction to calculate the total isotopic activity present in the waste cut. The waste cut uncertainty and bias is calculated by analyzing the uncertainties and biases in the waste stream characterization and waste cut measurements and adding the uncertainties in quadrature and multiplying the reported isotopic activities by the bias factors. The current isotopic inventory, uncertainty, and bias of a disposal unit is the sum of the currently disposed individual waste cut isotopic activities, uncertainties, and biases. The future uncertainty and bias is estimated based on the average “worst-case” (largest) uncertainties and biases of currently closed and operational disposal units. This report details the method, data sources, and calculation techniques used to calculate these values. It also presents some of the difficulties in working with the reported data and gives examples of the calculations and analysis. The software used to carryout the analysis is included and the location of the complete individual analyses is given. After discussion with waste generators, examination of multiple waste characterization documents, and a review of SRS Manual 1S, the reported ELLWF radionuclide activities are clearly conservative and likely represent reasonable upper bounds for the true activities. However, quantifying the bias and uncertainty in each waste cut requires detailed analysis of the documentation for each waste cut measurement and waste stream characterization.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS1986

The reality of the secular change in solar wind nitrogen isotopes

Evidence concerning the isotopic composition of N in the early solar system currently seems to favor a picture of isotopic inhomogeneity rather than of a unique primordial composition modified by local processes. Certainly the range of N-15/N-14 ratios found in meteorites points to the existence of more than one nucleogenetic N component, though mass dependent modification of them explain the isotopic variation observed for N in the lunar regolith. The observational evidence is addressed which can be used to discriminate between such a model and one invoking a secular change in the composition of the solar wind. Three tests of this model were considered, starting with a search for light planetary N surviving in lunar rocks. Results so far are negative. The results of these tests may not eliminate the two component model for regolith N but they seriously weaken it. The alternate view, involving a secular change in solar wind N composition, has its problems but continues to survive by default.

Kerridge, J. F.↗
NASA NTRS2009

Ethane's 12C/13C Ratio in Titan: Implications for Methane Replenishment

As the .main destination of carbon in the destruction of methane in the atmosphere of Titan, ethane provides information about the carbon isotopic composition of the reservoir from which methane is replenished. If the amount of methane entering the atmosphere is presently equal to the amount converted to ethane, the 12C/13C ratio in ethane should be close to the ratio in the reservoir. We have measured the 12C/13C ratio in ethane both with Cassini CIRS(exp 1) and from the ground and find that it is very close to the telluric standard and outer planet values (89), consistent with a primordial origin for the methane reservoir. The lower 12C/13C ratio measured for methane by Huygens GCMS (82.3) can be explained if the conversion of CH4 to CH3 (and C2H6) favors 12C over 13C with a carbon kinetic isotope effect of 1.08. The time required for the atmospheric methane to reach equilibrium, i.e., for replenishment to equal destruction, is approximately 5 methane atmospheric lifetimes.

Jennings, Donald E.↗
NASA NTRS2003

About Tagish Lake as a Potential Parent Body for Polar Micrometeorites; Clues from their Hydrogen Isotopic Compositions

The origin of the Antarctic micrometeorites (AMMs) is still a matter of debate. Their closest meteoritic counterparts are the C2 chondrites, but the match is not perfect, and the parent body(ies) of the AMMs is(are) still to be identified. Tagish Lake is a new meteorite fall which bears similarity with CI1 and CM2 chondrites, but is distinct from both. Based on the mineralogy of phyllosilicates, Noguchi et al. proposed that the phyllosilicate-rich AMMs and the Tagish Lake meteorites could derive from similar asteroids. The hydrogen isotopic compositions of extra-terrestrial samples can be used to get some insight on their origin. The D/H ratios of AMMs and of Tagish Lake have been measured, but using different analytical techniques. They are therefore not directly comparable. We performed additional hydrogen isotopic analyses of fragments of Tagish Lake using the same experimental setup previously used for the measurement of the hydrogen isotopic composition of AMMs. In this work, we could also analyze separately both lithologies of Tagish Lake (carbonate-poor and -rich). The distributions of delta D values measured in the two lithologies of Tagish Lake are very similar, indicating that fluids with similar hydrogen isotopic compositions altered the meteorite on the parent body for the two lithologies. Yet, the hydrogen isotopic composition of Tagish Lake is different from that of AMMs, suggesting that they do not derive from the same parent body.

Engrand, C.↗
NASA NTRS1988

Pb isotope constaints on the extent of crustal recycling into a steady state mantle

Isotopic and geochemical evidence was discussed against recycling of continental crust into the mantle. Element ratios such as Sm/Nd, Th/Sc, and U/Pb in sedimentary masses have remained relatively constant throughout Earth history, and this can only be reconciled with steady state recycling models if new crustal materials added from the mantle have had similar ratios. Such recycling models would also require shorter processing times for U, Th, and Pb through the mantle than are geodynamically reasonable. Models favoring subduction of pelagic sediments as the only recycling mechanism fail to account for the Pb isotopic signature of the mantle. Recycling of bulk crust with Pb isotopic compositions similar to those expected for primitive mantle would be permissable with available data, but there appear to be no plausible tectonic mechanisms to carry this out.

Galer, S. J. G.↗
NASA NTRS1986

Sr, Nd, and Pb isotopes in Proterozoic intrusives astride the Grenville Front in Labrador - Implications for crustal contamination and basement mapping

Trace element and Pb, Sr, and Nd isotopic compositions of anorthosites and related rocks, and of younger mafic dikes from Harp Lake and Mealy Mountains in Labrador, Canada are estimated and compared. The effects of crustal component contaminants on the isotopic compositions of the dikes are investigated. The correlation between the isotopic data and the crustal contamination model is studied. It is observed that for Harp Lake the initial Sr ratios are higher and the Nd values are lower than Mealy samples, and the data do not correspond to the crustal contamination model; however, the Pb isotope data favor a crustal contamination model. It is noted that the Labrador segment of the Grenville Front appears to coincide with the southern margin of the Archean North Atlantic craton, and may represent a pre mid-Proterozoic suture.

Ashwal, L. D.↗
NASA NTRS2020

Mantle-melt Partitioning of the Highly Siderophile Elements: New Results and Application to Mars

Trace elements and extant and extinct isotopic attributes in martian meteorites have been used to argue that Mars accreted quickly, differentiated into core and mantle, and established several mantle reservoirs, possibly within 10 Ma of T0. The partitioning of trace elements in the deep mantle has been relatively unstudied, despite the need for such knowledge in understanding magma ocean crystallization and the origin of depleted and enriched mantle reservoirs. The siderophile element composition of the martian mantle, and lithophile isotopic systems such as Sr, Hf, and Nd, are thought to record evidence for early metal-silicate equilibrium and deep magma ocean at an intermediate depth and pressure of 800 km or 14 GPa. We have carried out experiments across this pressure range to better understand the mineral/melt partitioning of a wide range of elements. These new data are used to evaluate differentiation models for Mars and to help interpret the available isotopic data. The relatively incompatible nature of Re compared to mildly compatible Os means that the crystallization of a deep magma ocean will lead to residual liquids with super chondritic Re/Os, and solids with sub-chondritic Re/Os. Such material available in the mantle could be the source of enriched isotopic reservoir that produced shergottites with + Os values. On the other hand, slightly sub-chondritic Re/Os ratios in the crystallizing solids would provide a reservoir that could produce - Os values. Melting of mixtures of these two enriched and depleted end members could explain the Nd-Os isotopic correlations and systematics of shergottites.

K Righter↗
DOE OSTI2024

Shifting groundwater fluxes in bedrock fractures: Evidence from stream water radon and water isotopes

Geologic features (e.g., fractures and alluvial fans) can play an important role in the locations and volumes of groundwater discharge and degree of groundwater-surface water (GW-SW) interactions. However, the role of these features in controlling GW-SW dynamics and streamflow generation processes are not well constrained. GW-SW interactions and streamflow generation processes are further complicated by variability in precipitation inputs from summer and fall monsoon rains, as well as declines in snowpack and changing melt dynamics driven by warming temperatures. Using high spatial and temporal resolution radon and water stable isotope sampling and a 1D groundwater flux model, we evaluated how groundwater contributions and GW-SW interactions varied along a stream reach impacted by fractures (fractured-zone) and below the fractured hillslope (non-fractured zone) in Coal Creek, a Colorado River headwater stream affected by summer monsoons. During early summer, groundwater contributions from the fractured zone dominated, but declined throughout the summer. Groundwater contributions from the non-fractured zone were constant throughout the summer and became proportionally more important later in the summer. We hypothesize that groundwater in the non-fractured zone is dominantly sourced from a high-storage alluvial fan at the base of a tributary that is connected to Coal Creek throughout the summer and provides consistent groundwater influx. Water isotope data revealed that Coal Creek responds quickly to incoming precipitation early in the summer, and summer precipitation becomes more important for streamflow generation later in the summer. We quantified the change in catchment dynamic storage and found it negatively related to stream water isotope values, and positively related to modeled groundwater discharge and the ratio of fractured zone to non-fractured zone groundwater. Importantly, we interpret these relationships as declining hydrologic connectivity throughout the summer leading to late summer streamflow supported predominantly by shallow flow paths, with variable response to drying from geologic features based on their storage. As groundwater becomes more important for sustaining summer flows, quantifying local geologic controls on groundwater inputs and their response to variable moisture conditions may become critical for accurate predictions of streamflow.

54 ENVIRONMENTAL SCIENCES↗