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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 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Isotopic Constraints on the Nature of Primary Precipitates in Archean–Early Paleoproterozoic Iron Formations from Determinations of the Iron Phonon Density of States of Greenalite and 2L- and 6L-Ferrihydrite

Iron formations (IFs) are chemical sedimentary rocks that were widely deposited before the Great Oxidation Event (GOE) around 2.4- 2.2 Ga. It is generally thought that IFs precipitated as hydrated Fe 3+ oxides (HFOs) such as ferrihydrite following surface oxidation of Fe 2+ -rich, anoxic deep waters. This model often implicates biological oxidation and underpins reconstructions of marine nutrient concentrations. However, nanoscale petrography indicates that an Fe 2+ silicate, greenalite, is a common primary mineral in well-preserved IFs, motivating an alternative depositional model of anoxic ferrous silicate precipitation. It is unclear, however, if Fe 2+ -rich silicates can produce the Fe isotopic variations in IFs that are well explained by Fe 2+ oxidation. To address this question, we constrain the equilibrium Fe isotopic ( 56 Fe/ 54 Fe) fractionation of greenalite and ferrihydrite by determining the iron phonon densities of states for those minerals. Here, we use ab initio density functional theory (DFT + U) calculations and nuclear resonant inelastic X-ray scattering spectroscopy to show that ferrous greenalite should be isotopically lighter than ferrihydrite by similar to 1-1.2 parts per thousand at equilibrium, and fractionation should scale linearly with increasing Fe 3+ content in greenalite. By anchoring ferrihydrite-greenalite mineral pair fractionations to published experimental Fe isotopic fractionations between HFOs and aqueous Fe 2+ , we show that ferrous greenalite may produce all but the heaviest pre-GOE Fe isotopic compositions and mixed valence greenalites can produce the entire record. Our results suggest that heavy Fe isotope enrichments alone are not diagnostic of primary IF mineralogies, and ferrihydrite and partially oxidized or even purely ferrous greenalite are all viable primary IF mineralogies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

The Magnetized Indirect Drive Project on the National Ignition Facility

A new project is underway at the National Ignition Facility with the goal of applying a seed magnetic field to the fusion fuel in an indirect drive hohlraum implosion and quantifying the effect on the hot-spot temperature, shape and neutron yield. Magnetizing fusion fuel is calculated to reduce heat loss from the implosion core by constraining the motion of electrons and fusion-generated alpha particles; this can improve the chances of achieving high-gain fusion in a laboratory plasma. Here, we describe the goals of this project and the significant scientific and technological challenges which must be overcome for this project to succeed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Absolute Decay Counting of $$^{146}$$Sm and $$^{147}$$Sm for Early Solar System Chronology

Sm-Nd chronometers use 146 Sm and 147 Sm to determine the ages of major events in the early Solar System. Their half-lives are the most important nuclear parameters deter mining the accuracy of chronometry. However, the 146 Sm half-life is not well-established: the published values differ by ~30%, which results in significant uncertainties in the So lar System timeline. We are re-measuring the half-lives of 146 Sm and 147 Sm using decay energy spectroscopy and metallic magnetic calorimeters to improve the accuracy of the Sm Nd chronometers. We report recent experimental results from our first measurement of a 147 Sm source, as well as status and plans for experiments on 146 Sm.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Chemical separation of 146 Sm for half-life determination

Here, although methods for the chemical separation of samarium from a rock matrix are well established, chemical separation of samarium from non-natural isotopic impurities for the purpose of 146 Sm half-life measurement requires modifications to these procedures, as well as additional checks for effective separation. This work describes the chemical purification procedures associated with the 146 Sm source and the results from gamma spectroscopy. The purification procedure allowed for the quantitative determination of the number of 146Sm atoms using a modified isotope dilution technique. Alpha-decay counting of the sample will be applied in the future to determine the half-life of 146 Sm.

146Sm↗
DOE OSTI2023

Densification and microstructure features of lithium hydride fabrication

The manufacturing of lithium hydride (LiH) utilizing uniaxial pressing, which offers fabrication with tailorable properties via microstructure control, can lead to the expansion in application of LiH while bypassing the challenges presented by historical casting manufacturing techniques. Through control of consolidation conditions such as pressure, temperature, dwell time and powder load, the presented work highlights the densification of LiH, with an emphasis on quantifying oxygen content, for applications requiring a specific density range necessary for optimized material performance. Karl Fischer Titration and X-ray Diffraction proved useful in determining oxygen and phase content while Computed Tomography and Scanning Electron Microscopy provided structural analysis. The temperature dependent densification of LiH fit with an Arrhenius term resulted in an activation energy of 21.2 kJ/mol. Images of fractured surfaces of LiH pressed at 500 °C revealed drastic grain coarsening, aided by the presence of oxygen impurities.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Determination of impurities in cubic boron nitride (cBN) by inductively coupled plasma mass spectrometry (ICPMS)

The phase stability of cBN is critically dependent on the content and amount of impurities present. While studies have shown qualitatively that the addition of certain impurities can either increase or decrease the cBN-hBN phase transition temperature, studies have yet to show this effect quantitatively. This is because analytical methods to characterize minor and trace impurities in cBN are currently lacking. To this end, we present flux fusion methods capable of fully digesting cBN samples for ICPMS analyses. The materials used in this study are commercially available cBN powders in three different sizes. Two types of fluxes (LiOH and NaOH·H 2 O) are utilized so that both Li and Na impurities can be determined. To ensure the accuracy of Si measurements, a column chromatography method has been developed to purify Si from flux materials in order to increase the amount of dissolved sample sent to the ICP. Detection limits have been determined using procedural blanks and are found to be below 20 μg/g for all 58 elements analyzed except for Si, for which the detection limit is 312 μg/g. Nonetheless, all cBN powders studied are found to have high Si impurity levels that are above detection limit. This study provides a much-needed analytical protocol to enable comprehensive screening of impurities in cBN.

36 MATERIALS SCIENCE↗
DOE OSTI2020

The timing of lunar solidification and mantle overturn recorded in ferroan anorthosite 62237

Ferroan anorthosite suite (FAS) rocks are widely interpreted to represent primordial lunar crust. Despite their importance in pinpointing the timing of lunar crust formation, robust chronological investigations for this rock type are scarce. Here, we report the Ar-Ar, Rb-Sr, and Sm-Nd isotopic systematics for the FAS troctolitic anorthosite 62237. The Ar-Ar isotopic system has been reset by a thermal event at 3710 ± 48 Ma, and the Rb-Sr isotopic systematics has been disturbed such that a Rb-Sr isochron age cannot be determined. However, an internal isochron for the Sm-Nd isotopic system has yielded an age of 4350 ± 73 Ma (MSWD = 2.0) with an initial ε 143 Nd CHUR of -0.53 ± 0.26. The mineral and whole-rock fractions of 62237 plot on the same internal isochron as FAS sample 60025. The combined datasets define an age of 4372 ± 35 Ma (MSWD = 4.0) with an initial ε 143 Nd CHUR of -0.17 ± 0.22. Literature Sm-Nd data for FAS and Mg-suite whole-rocks also plot on the 60025-62237 isochron. The coherence of data from both FAS and Mg-suite rocks examined thus far suggests that both rock suites formed contemporaneously from identical, or nearly identical, sources. In addition, the concordance of FAS and Mg-suite ages suggests that primordial crust solidification either involved both magmatic suites, or that Mg-suite magmatism was contemporaneous with FAS magmatism within resolution of the Sm-Nd chronometer. The ages for FAS and Mg-suite also coincide with the formation ages of the mare basalt source regions and urKREEP. Ferroan anorthosite suite rocks and urKREEP are thought to represent primordial LMO solidification products, whereas Mg-suite and the mare basalt source regions are argued to represent mixtures of various LMO crystallization products that were formed during density-driven overturn of the LMO. The concordance of ages implies that the 4372 ± 35 Ma Sm-Nd isochron records the age of mantle overturn, and that overturn occurred during, or shortly after, solidification of the LMO.

58 GEOSCIENCES↗
DOE OSTI2020

Onset of magma ocean solidification on Mars inferred from Mn-Cr chronometry

The mantle of Mars probably differentiated through the crystallization of a magma ocean during the first tens of million years (Ma) of Solar System evolution. However, the exact timescale of large-scale silicate differentiation of the martian mantle is debated, and in particular, it remains unclear when differentiation commenced. In this paper, we applied the short-lived 53 Mn- 53 Cr system to martian meteorites in order to date the onset of large-scale mantle differentiation on Mars. The new Cr isotope data demonstrate that martian meteorites exhibit no resolvable radiogenic 53 Cr variations, and instead have a uniform +20.2±1.2 (95% conf.) parts-per-million excess in 53 Cr/ 52 Cr relative to the terrestrial mantle. The investigated groups of martian meteorites are lithologically varied and derive from diverse mantle sources that probably had variable Mn/Cr. Hence, the lack of 53 Cr variability among martian meteorites demonstrates that silicate differentiation on Mars occurred after the extinction of 53 Mn. Provided that the sources of the martian meteorites have Mn/Cr variations that are typical of the terrestrial planets, this result implies that the onset of large-scale silicate differentiation must have occurred later than 20±5 Ma after Solar System formation. The onset of silicate differentiation on Mars inferred here is significantly later than time estimates for segregation of the martian core which conservatively occurred within <10 Ma after Solar System formation. Thus, the new Mn-Cr data imply that there was a small, but resolvable, time gap of at least 5 Ma between core formation and magma ocean solidification on Mars. If the age of core segregation is taken at face value, our results imply that the martian magma ocean remained mostly molten over several Ma. This inferred longevity of the magma ocean is inconsistent with thermal models predicting rapid (<1 Ma) solidification of the martian magma ocean. Although there is currently no unique solution to this conundrum, our results can potentially be explained by a protracted history of impact bombardment that delayed differentiation in a shallow magma ocean on Mars, or perhaps more readily, by the presence of an early and dense atmosphere that acted as an insulator and prevented the magma ocean from cooling quickly.

58 GEOSCIENCES↗
DOE OSTI2021

The gallium isotopic composition of the Moon

Here, in this study, we present new Ga isotope data from a suite of 28 mare basalts and lunar highland rocks. The δ 71 Ga values of these samples range from -0.10 to +0.66‰ (where δ 71 Ga is the relative difference between the 71 Ga/ 69 Ga ratio of a sample and the Ga-IPGP standard), which is an order of magnitude more heterogeneous than δ 71 Ga values in terrestrial magmatic rocks. The cause of this isotopic heterogeneity must be established to estimate the bulk δ 71 Ga value of the Moon. In general, low-Ti basalts and ferroan anorthosite suite (FAS) rocks have δ 71 Ga values that are lower than high-Ti basalts and KREEP-rich rocks. The observation that rocks derived from later forming LMO cumulates have higher δ 71 Ga values suggests that Ga isotopes are fractionated by processes that operate within the chemically evolving LMO, rather than localized degassing or volatile redistribution. Correlations between indices of plagioclase removal from the LMO (e.g. Eu/Eu*) with Ga isotope ratios suggest that a Δ 71 Ga plagioclase-melt of -0.3‰, (where Δ 71 Ga plagioclase-melt is the isotopic fractionation associated with crystallization of plagioclase from a melt), could drive the observed isotopic fractionation in high-Ti mare basalts and KREEP-rich rocks. This would be consistent with the observation that FAS rocks have δ 71 Ga values that are lower than mare basalts. However, the addition of KREEP-like material into the mare basalt source regions would not contribute enough Ga to perturb the isotopic composition outside of analytical uncertainty. Thus, basalts derived from early formed LMO cumulates such as those from Apollo 15, would preserve light Ga isotopic compositions despite containing modest amounts of urKREEP. We estimate that the δ 71 Ga value of the LMO was ~0.14‰ prior to the onset of plagioclase crystallization and extraction. Whether this δ 71 Ga value is representative of the initial BSM cannot be ascertained from the current dataset. It remains plausible that the Moon accreted with a heavier Ga isotopic composition than the Earth. Alternatively, the Moon and Earth could have accreted with similar isotopic compositions (BSE = 0.00 ± 0.06‰, Kato et al., 2017) and volatile loss drove the LMO to higher δ 71 Ga values prior to formation of the lunar crust.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Iron, magnesium, and titanium isotopic fractionations between garnet, ilmenite, f ayalite, biotite, and tourmaline: Results from NRIXS, ab initio , and study of mineral separates from the Moosilauke metapelite

Interpreting isotopic signatures documented in natural rocks requires knowledge of equilibrium isotopic fractionation factors. Here, we determine equilibrium Fe isotope fractionation factors between several common rock-forming minerals using a comparative approach involving three independent methods: (i) isotopic analyses of natural minerals from a metapelite from Mt. Moosilauke, New Hampshire, for which equilibration temperature and pressure are well constrained to be near the aluminosilicate triple point (T ≃ 500 °C, P ≃ 4 kbar), (ii) Nuclear Resonant Inelastic X-ray Scattering (NRIXS) measurements of Fe force constants of minerals, and (iii) Density Functional Theory (DFT) ab initio calculations of Fe force constants of minerals. The minerals studied for Fe isotopes include, in increasing order of their β-factors: garnet < ilmenite ≈ fayalite < biotite < tourmaline < muscovite ≈ plagioclase. Some of this ordering is affected by the presence of Fe 3+ in the minerals, which tends to form stiffer bonds and be associated with heavy Fe isotope enrichments relative to Fe 2+ . We are, however, able to assess the magnitude of the effect of the ratio Fe 3+ /ΣFe on equilibrium fractionation factors, notably on the ilmenite-hematite solid solution. Equilibrium Fe isotopic fractionation factors between garnet, ilmenite, biotite, tourmaline and fayalite are determined. We also report Mg and Ti isotopic compositions of selected Moosilauke minerals that allow us to better constrain the equilibrium fractionation factors for garnet-biotite-tourmaline (Mg isotopes) and biotite-ilmenite (Ti isotopes). We show how the newly determined equilibrium fractionation factors can be used to address diverse problems in Earth and planetary sciences, notably (i) Fe and Mg isotopic fractionation during anatexis, (ii) Fe isotopic fractionation in lunar ilmenite, and (iii) Ti isotopic fractionation during fluvial transport of minerals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Equilibrium Fe isotope fractionation between olivine, pyroxene, spinel and MORB glass: Implications for mantle partial melting to generate MORBs

Primitive mid-ocean ridge basalts (MORBs) exhibit Fe isotopic compositions heavier than the upper mantle by +0.074 ± 0.028 ‰ for δ 56 Fe. The processes responsible for this isotopic difference remain unclear. Modeling of Fe isotope fractionation during mantle partial melting requires reliable equilibrium Fe isotope fractionation factors between minerals and melts, for which consistent data are still lacking. Here, in this study, we used Nuclear Resonant Inelastic X-ray Scattering (NRIXS) technique to measure Fe force constants for a MORB glass (ALV 519-4-1) and natural mantle minerals (olivine, orthopyroxene, clinopyroxene, and spinel) to determine the equilibrium Fe isotope fractionation factors between them. The force constants determined in this study, in increasing order, are 167 ± 26 N/m for spinel, 175 ± 17 N/m for olivine, 176 ± 20 N/m for MORB glass, 205 ± 26 N/m for clinopyroxene, and 219 ± 36 N/m for orthopyroxene. We evaluated the previously proposed mechanisms for the heavy Fe isotopic composition of MORBs, including (i) mantle partial melting, (ii) mantle lithological heterogeneity, with pyroxenite in the source, (iii) mantle metasomatism by low-degree melts, and (iv) fractional crystallization of olivine from melts. For (i), we used the pMELTS program to simulate adiabatic decompression melting of mantle peridotites, and calculated Fe isotope fractionation based on Fe 3+ –Fe 2+ equilibrium-controlled fractionation, where Fe 3+ forms stronger bonds and is more incompatible than Fe 2+ . At 10 wt% peridotite melting, corresponding to MORB generation, only +0.03 ‰ Fe isotope fractionation between the melt and the original bulk composition (Δ 56 Fe = δ 56 Fe melt - δ 56 Fe 0 ) was produced, insufficient to account for the observed MORB-upper mantle difference. For (ii), melting of pyroxenites yields smaller Fe isotope fractionation than melting of peridotites, making it unlikely the cause for the MORB-upper mantle isotopic difference. For (iii), both the Fe 3+ /ΣFe ratio and the δ 56 Fe of melts increase with the degree of partial melting, indicating that low-degree melts are not isotopically heavy enough to significantly alter the isotopic composition of lithospheric mantle through metasomatism. For (iv), equilibrium isotope fractionation between olivine and melt is near zero. These results suggest that equilibrium Fe isotope fractionation alone cannot explain the MORB isotopic signature, highlighting the potential role of kinetic isotope fractionation. Using a diffusion model, we calculated kinetic Fe and Mg isotope fractionations associated with (iv) olivine crystallization from a melt, and found that the predicted Fe and Mg isotope fractionations were inconsistent with observations in MORBs. Qualitatively, two processes could have induced kinetic Fe isotope fractionation during MORB generation: (a) Fe-Mg interdiffusion between melt and solid during melt migration and (b) reactive melt-rock interactions during melt focusing. However, a quantitative understanding of their role in modifying the melt isotopic composition remains limited and requires further investigation.

Fe isotopes↗
DOE OSTI2026

Suppression and enhancement of electromagnetic pulses from laser–target interactions by strong magnetic fields

Laser–target interactions generate intense electromagnetic pulses (EMPs) that can interfere with measurements and damage equipment. In this paper we show that applying a magnetic field to nanosecond pulse laser–target interactions decreases the magnitude of EMPs. We demonstrate this effect in two experiments with different geometries (spherical versus planar), laser intensities ( ∼10 13 versus ∼10 15 W/cm 2 ) and applied field strength (12 versus 0.1 T) that both observed suppression of EMPs in approximately the 1 GHz band (by factors of 0.65× and 0.32×, respectively). We then observe the opposite effect at high intensities with a picosecond pulse: for planar experiments with laser intensities of approximately 10 19 W/cm 2 and magnetic fields of 6–10 T, the magnitude of EMPs is increased by a factor of 1.75×. These results provide a benchmark for models of EMP generation, but suggest that magnetic fields are not a viable solution for mitigating EMPs in the high-intensity laser facilities where they are most damaging.

electromagnetic pulse↗
DOE OSTI2026

Signatures of Antisymmetric Vibrations in the Ultrafast Dynamics of Quadrupolar Dyes

Antisymmetric molecular vibrations are central to ultrafast, nonadiabatic photophysical and photochemical processes such as conical intersection dynamics, Herzberg–Teller couplings and, potentially, singlet fission. Direct spectroscopic identification of such vibrations is, however, challenging, since they are typically Raman inactive and affect optical transitions only weakly. Here, we report experimental signatures of vibronic couplings to a high-frequency antisymmetric vibration in the excited state dynamics of a quasi-quadrupolar molecule by ultrafast two-dimensional electronic spectroscopy (2DES). The early time, sub-50 fs 2DES maps reveal an asymmetric peak pattern with characteristic low-energy cross-peaks. We show that these peaks arise from stimulated emission transitions from an anharmonic, double-minimum excited state potential energy surface formed by vibronic coupling to a high-frequency antisymmetric mode. Simulations based on a phenomenological essential state model support the results. Our findings offer a new approach for identifying antisymmetric vibrations in ultrafast 2DES and track excited state wavepacket motion before relaxation washes out the spectra.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Roadmap for Photonics with 2D Materials

Triggered by advances in atomic-layer exfoliation and growth techniques, along with the identification of a wide range of extraordinary physical properties in self-standing films consisting of one or a few atomic layers, two-dimensional (2D) materials such as graphene, transition metal dichalcogenides (TMDs), and other van der Waals (vdW) crystals now constitute a broad research field expanding in multiple directions through the combination of layer stacking and twisting, nanofabrication, surface-science methods, and integration into nanostructured environments. Photonics encompasses a multidisciplinary subset of those directions, where 2D materials contribute remarkable nonlinearities, long-lived and ultraconfined polaritons, strong excitons, topological and chiral effects, susceptibility to external stimuli, accessibility, robustness, and a completely new range of photonic materials based on layer stacking, gating, and the formation of moiré patterns. These properties are being leveraged to develop applications in electro-optical modulation, light emission and detection, imaging and metasurfaces, integrated optics, sensing, and quantum physics across a broad spectral range extending from the far-infrared to the ultraviolet, as well as enabling hybridization with spin and momentum textures of electronic band structures and magnetic degrees of freedom. The rapid expansion of photonics with 2D materials as a dynamic research arena is yielding breakthroughs, which this Roadmap summarizes while identifying challenges and opportunities for future goals and how to meet them through a wide collection of topical sections prepared by leading practitioners.

2D materials↗
DOE OSTI2022

Charge Delocalization and Vibronic Couplings in Quadrupolar Squaraine Dyes

Squaraines are prototypical quadrupolar charge-transfer chromophores that have recently attracted much attention as building blocks for solution-processed photovoltaics, fluorescent probes with large two-photon absorption cross sections, and aggregates with large circular dichroism. Their optical properties are often rationalized in terms of phenomenological essential state models, considering the coupling of two zwitterionic excited states to a neutral ground state. As a result, optical transitions to the lowest S 1 excited state are one-photon allowed, whereas the next higher S 2 state can only be accessed by two-photon transitions. A further implication of these models is a substantial reduction of vibronic coupling to the ubiquitous high-frequency vinyl-stretching modes of organic materials. Here, in this study, we combine time-resolved vibrational spectroscopy, two-dimensional electronic spectroscopy, and quantum-chemical simulations to test and rationalize these predictions for nonaggregated molecules. We find small Huang–Rhys factors below 0.01 for the high-frequency, 1500 cm –1 modes in particular, as well as a noticeable reduction for those of lower frequency modes in general for the electronic S 0 → S 1 transition. The two-photon allowed state S 2 is well separated energetically from S 1 and has weak vibronic signatures as well. Thus, the resulting pronounced concentration of the oscillator strength in a narrow region relevant to the lowest electronic transition makes squaraines and their aggregates exceptionally interesting for strong and ultrastrong coupling of excitons to localized light modes in external resonators with chiral properties that can largely be controlled by the molecular architecture.

36 MATERIALS SCIENCE↗