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All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Age determination of a 75 Se gamma radiography source for nuclear forensics

Here, two methods were used to evaluate the age of 75 Se sealed source material. Both methods utilized gamma spectroscopy to determine the quantity of parent 75 Se present, but they differed in the technique used to determine the quantity of daughter 75 As. In one method, 75 As was quantified using inductively coupled plasma-mass spectrometry (ICP-MS) after using chromatographic techniques to separate the parent and daughter isotopes. In the other method, total As was measured using optical emission spectroscopy (OES), which did not require separation prior to measurement. The OES method was faster and gave slightly lower uncertainties, but required more daughter material to be present because of higher concentration requirements, making it unsuitable for young material. Both methods are hampered by the monoisotopic nature of As, but still gave reasonable model ages that were in agreement with each other.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
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 OSTI2021

Determination of affinities of lanthanide-binding proteins using chelator-buffered titrations

The recent discoveries of the first proteins that bind lanthanides as part of their biological function not only are relevant to the emerging field of lanthanide-dependent biology, but also hold promise to revolutionize the technologically critical rare earths industry. Although protocols to assess the thermodynamics of metal–protein interactions are well established for “traditional” metal ions in biology, the characterization of lanthanide-binding proteins presents a challenge to biochemists due to the lanthanides' Lewis acidity, propensity for hydrolysis, and high-affinity complexes with biological ligands. These properties necessitate the preparation of metal stock solutions with very low buffered “free” metal concentrations (e.g., femtomolar to nanomolar) for such determinations. Here in this paper we describe several protocols to overcome these challenges. First, we present standardization methods for the preparation of chelator-buffered solutions of lanthanide ions with easily calculated free metal concentrations. We also describe how these solutions can be used in concert with analytical methods including UV–visible spectrophotometry, circular dichroism spectroscopy, Förster resonance energy transfer (FRET), and sensitized terbium luminescence, in order to accurately determine dissociation constants (K d s) of lanthanide–protein complexes. Finally, we highlight how application of these methods to lanthanide-binding proteins, such as lanmodulin, has yielded insights into selective recognition of lanthanides in biology. We anticipate that these protocols will facilitate discovery and characterization of additional native lanthanide-binding proteins, will motivate the understanding of their biological context, and will prompt their applications in biotechnology.

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

Grain incompatibility determines the local structure of amorphous grain boundary complexions

Amorphous grain boundary complexions lack long-range crystalline order but are not featureless, as distinct gradients in structural short-range order have been reported through their thickness. In this work, we test the hypothesis that the distribution of short-range order is determined by the confining crystals using atomistic simulations of both Cu-Zr bicrystals and a random polycrystal. Voronoi polyhedra with structures similar to that of perfect face-centered cubic serve as signatures of high structural order and are only found at the amorphous-crystalline transition regions. The density of the ordered structural motifs within a specific amorphous-crystalline transition region is found to not be directly determined by the orientation and symmetry of the grain which touches it, but rather by the incompatibility between the two confining grains. Further, ordered polyhedra density is found to be inversely related to grain incompatibility, meaning that large incompatibilities between the confining crystals lead to less order in the amorphous-crystalline transition region. The finding that the entire grain-film-grain system must be considered to understand local structure unequivocally demonstrates that amorphous complexions are not simply a collection of independent phases which happen to nucleate at a grain boundary. Rather, an amorphous grain boundary complexion is a single entity that finds a local equilibrium configuration.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Use of Compton suppression gamma ray spectrometry to determine 239 Pu

We report 239 Pu has been characterized by gamma-ray spectroscopy for a level higher than the usual environmental ones typically needing alpha spectrometry, ICP-MS or TIMS. The higher activities typically have applications in reprocessing, safeguards verification, and nuclear forensics. For activities of hundreds of Bq/g, it is possible to use gamma ray spectrometry for 239 Pu characterization. A soil reference standard of 185 Bq/g (75 ng/g) was measured on a 79% efficient HPGe with a digital Compton suppression system. The ratios of the counting statistics for suppressed and unsuppressed uncertainties for various 239 Pu photopeaks were determined. The effects of self-attenuation on the low energy gamma rays were evaluated, and it was determined that Compton suppression was an effective characterization method of 239 Pu after accounting for self-attenuation.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Membrane hydrophobicity determines the activation free energy of passive lipid transport

The collective behavior of lipids with diverse chemical and physical features determines a membrane's thermodynamic properties. Yet, the influence of lipid physicochemical properties on lipid dynamics, in particular interbilayer transport, remains underexplored. Here, we systematically investigate how the activation free energy of passive lipid transport depends on lipid chemistry and membrane phase. Through all-atom molecular dynamics simulations of 11 chemically distinct glycerophospholipids, we determine how lipid acyl chain length, unsaturation, and headgroup influence the free energy barriers for two elementary steps of lipid transport: lipid desorption, which is rate limiting, and lipid insertion into a membrane. Consistent with previous experimental measurements, we find that lipids with longer, saturated acyl chains have increased activation free energies compared to lipids with shorter, unsaturated chains. Lipids with different headgroups exhibit a range of activation free energies; however, no clear trend based solely on chemical structure can be identified, mirroring difficulties in the interpretation of previous experimental results. Compared to liquid-crystalline phase membranes, gel phase membranes exhibit substantially increased free energy barriers. Overall, we find that the activation free energy depends on a lipid's local hydrophobic environment in a membrane and that the free energy barrier for lipid insertion depends on a membrane's interfacial hydrophobicity. Both of these properties can be altered through changes in lipid acyl chain length, lipid headgroup, and membrane phase. Thus, the rate of lipid transport can be tuned through subtle changes in local membrane composition and order, suggesting an unappreciated role for nanoscale membrane domains in regulating cellular lipid dynamics.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Fe Kα XANES, Fe Kβ HERFD XANES and EPMA flank method determinations of the oxidation state of Fe in garnet

The ferric to total iron ratios (Fe 3+ /ΣFe) of garnets can be paired with thermodynamic mineral activity models to quantify the oxygen fugacity of garnet-bearing rocks. However, techniques with a high analytical and spatial resolution are necessary to distinguish differences in garnet Fe 3+ /ΣFe ratios at the percent level and to accurately measure garnets that are zoned or contain inclusions. We acquired conventional Fe Kα and high-resolution energy fluorescence detection (HERFD) Fe Kβ X-ray absorption near edge structure (XANES) spectra and electron microprobe flank method analyses on a suite of 27 peridotitic and eclogitic garnets with Fe 3+ /ΣFe ratios previously determined by Mössbauer spectroscopy to evaluate the precision of each technique. We examined variations in the energy and intensity of three XANES spectral features as a function of Fe 3+ /ΣFe ratios: 1) the intensity ratio of two-post edge features (I-ratio; Fe Kα only); 2) the energy of the Fe edge at 90% normalized intensity (E 0.9 ; Fe Kα only) and 3) the pre-edge centroid energy (Fe Kα and HERFD Fe Kβ). In accordance with previous work, we find the energies of garnet pre-edge centroids are relatively insensitive to Fe 3+ /ΣFe ratios. The I-ratios of peridotitic and eclogitic garnets are offset from each other at low Fe 3+ /ΣFe ratios (≤0.13); I-ratio garnet XANES calibrations are composition-specific. The E 0.9 feature is independent of garnet major element composition in spectra that have been corrected for the effects of self-absorption. We produce two Fe Kα garnet XANES calibrations based on variations in the E0.9 feature; one calibration with all garnet reference materials included (Fe 3+ /ΣFe up to 1.0; “all garnet calibration”) and another calibration specific to garnets with low Fe 3+ /ΣFe ratios (“low ferric calibration”). Fe 3+ /ΣFe ratios calculated from the mean of up to 25 flank method measurements on eight garnet reference materials fall within 4% absolute of a one-to-one correlation with Fe 3+ /ΣFe ratios measured by Mössbauer. The standard error of the mean Fe 3+ /ΣFe ratio calculated from flank method approaches the Mössbauer-determined Fe 3+ /ΣFe ratio within estimated error (3%) after three analyses. Flank method precision is enhanced at higher beam current; however, the precision of the flank method does not approach the precision of XANES under any microprobe analytical condition tested here. Garnet reference materials detailed here are available by request to the Smithsonian Institution.

58 GEOSCIENCES↗
DOE OSTI2024

Principal Landau determinants

We reformulate the Landau analysis of Feynman integrals with the aim of advancing the state of the art in modern particle-physics computations. We contribute new algorithms for computing Landau singularities, using tools from polyhedral geometry and symbolic/numerical elimination. Inspired by the work of Gelfand, Kapranov, and Zelevinsky (GKZ) on generalized Euler integrals, we define the principal Landau determinant of a Feynman diagram. We illustrate with a number of examples that this algebraic formalism allows to compute many components of the Landau singular locus. We adapt the GKZ framework by carefully specializing Euler integrals to Feynman integrals. For instance, ultraviolet and infrared singularities are detected as irreducible components of an incidence variety, which project dominantly to the kinematic space. We compute principal Landau determinants for the infinite families of one-loop and banana diagrams with different mass configurations, and for a range of cutting-edge Standard Model processes. Furthermore, our algorithms build on the Julia package this http URL and are implemented in the new open-source package this http URL available at this https URL.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Genetic determinants of switchgrass-root-associated microbiota in field sites spanning its natural range

A fundamental goal in plant microbiome research is to determine the relative impacts of host and environmental effects on root microbiota composition, particularly how host genotype impacts bacterial community composition. Most studies characterizing the effect of plant genotype on root microbiota undersample host genetic diversity and grow plants outside of their native ranges, making the associations between host and microbes difficult to interpret. Here, we characterized the root microbiota of a large diversity panel of switchgrass, a North American native C4 bioenergy crop, in three field locations spanning its native range. Our data, composed of 1,961 samples, suggest that field location is the primary determinant of microbiome composition; however, substantial heritable variation is widespread across bacterial taxa, especially those in the Sphingomonadaceae family. Despite diverse compositions, relatively few highly prevalent taxa make up the majority of the switchgrass root microbiota, a large fraction of which is shared across sites. Local genotypes preferentially recruit/filter for local microbes, supporting the idea of affinity between local plants and their microbiota. Using genome-wide association, we identified loci impacting the abundance of >400 microbial strains and found an enrichment of genes involved in immune responses, signaling pathways, and secondary metabolism. We found loci associated with over half of the core microbiota (i.e., microbes in >80% of samples), regardless of field location. Finally, we show a genetic relationship between a basal plant immunity pathway and relative abundances of root microbiota. Furthermore, this study brings us closer to harnessing and manipulating beneficial microbial associations via host genetics.

54 ENVIRONMENTAL SCIENCES↗
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 OSTI2024

Component-based SHGC determination of BIPV glazing for product comparison

Building-integrated photovoltaic (BIPV) systems are intrinsically designed to generate electricity and to provide at least one building-related function. When BIPV modules act as glazing products in windows, skylights or curtain walls, their ability to control the transmission of solar energy into the building must be characterised by a Solar Heat Gain Coefficient (SHGC) or g value (also known as Total Solar Energy Transmittance – TSET – or “solar factor”). For the comparison of BIPV glazing products consisting of one PV laminate and possibly further, conventional glazing layers separated by gas-filled cavities, the procedures documented in international standards for architectural glazing (e.g. ISO 9050 and EN 410) form a suitable starting point. Easily implemented modifications to these procedures are proposed to take both optical inhomogeneity (if relevant) and extraction of electricity from BIPV glazing units into account. Geometrically complex glazing and shading devices, and light-scattering glazing layers, are outside the scope of the proposed methodology; SHGC determination for obliquely incident solar radiation is also excluded. For these cases, the experimental calorimetric approach documented in [ISO 19467:2017; ISO 19467-2:2021] is recommended. The paper also presents results and conclusions from an implementation exercise and sensitivity study carried out by participants of the IEA-PVPS Task 15 on BIPV. The cell coverage ratio in the PV laminate, the thermal resistance offered by the glazing configuration, the choice of boundary conditions and the effect of extracting electricity were all identified as parameters which significantly affect the SHGC value determined for a given type of BIPV glazing. A practicable approach to accommodate the great variety of dimensions typical for BIPV glazing is also proposed. These findings should pave the way for modifying the existing component-based standards for architectural glazing to take the specific features of BIPV glazing into account.

14 SOLAR ENERGY↗
DOE OSTI2022

Constraint-dependent CTOA determination for stable ductile crack growth

The crack tip opening angle (CTOA) has been used as a reliable fracture toughness to characterize stable crack growth for thin-wall structures in low-constraint conditions. Recently, it is found that CTOA can also be utilized as a robust fracture parameter to describe the arrest fracture toughness for gas transmission pipelines in ductile steels. For better understanding the concept of CTOA, this paper presents a brief review on the CTOA definitions and its test methods. And then, four CTOA models are developed for determining the CTOA toughness using conventional single edge notched bend (SENB) specimens, including the load–displacement linear fit model, the logarithmic load–displacement linear fit model, the stable tearing energy model, and the J-differentiation model. Here fracture test data from SENB specimens in A285 carbon steel are employed to evaluate the proposed CTOA models. The results show that these CTOA models can determine either identical or comparable critical CTOA values for stable ductile crack growth using the SENB specimens. A constraint-corrected CTOA resistance curve and a constraint-corrected critical CTOA equation are also obtained for A285 carbon steel.

42 ENGINEERING↗
DOE OSTI2022

Melting and phase relations of Fe-Ni-Si determined by a multi-technique approach

Many studies have suggested silicon as a candidate light element for the cores of Earth and Mercury. However, the effect of silicon on the melting temperatures of core materials and thermal profiles of cores is poorly understood, due to disagreements among melt detection techniques, uncertainties in sample pressure evolution during heating, and sparsity of studies investigating the combined effects of nickel and silicon on the phase diagram of iron. Here, in this study we develop a multi-technique approach for measuring the high-pressure melting and solid phase relations of iron alloys and apply it to Fe 0.8 Ni 0.1 Si 0.1 (Fe-11wt%Ni-5.3wt%Si), a composition compatible with recent estimates for the cores of Earth and Mercury. This approach combines results (20-83 GPa) from two atomic-level techniques: synchrotron Mossbauer spectroscopy (SMS) and synchrotron x-ray diffraction (XRD). Melting is independently detected by the loss of the Mossbauer signal, produced exclusively by solid-bound iron nuclei, and the onset of a liquid diffuse x-ray scattering signal. The use of a burst heating and background updating method for quantifying changes in the reference background during heating facilitates the determination of liquid diffuse signal onsets and leads to strong reproducibility and excellent agreement in melting temperatures determined separately by the two techniques. XRD measurements additionally constrain the hcp-fcc phase boundary and in-situ pressure evolution of the samples during heating. We apply our updated thermal pressure model to published SMS melting data on fcc-Fe and fcc-Fe 0.9 Ni 0.1 to precisely evaluate the effect of silicon on melting temperatures. We find that the addition of 10 mol% Si to Fe 0.9 Ni 0.1 reduces melting temperatures by ~250 K at low pressures (<60 GPa) and flattens the hcp-fcc phase boundary. Extrapolating our results, we constrain the location of the hcp-fcc-liquid quasi-triple point at 147±14 GPa and 3140±90 K, which implies a melting temperature reduction of 500 K compared with Fe 0.9 Ni 0.1 . The results demonstrate the advantages of combining complementary experimental techniques in investigations of melting under extreme conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Adaptive Interface-PINNs (AdaI-PINNs) for inverse problems: Determining material properties for heterogeneous systems

Here, we determine spatially varying discontinuous material properties using a domain-decomposition based physics-informed neural networks (PINNs) framework named the Adaptive Interface-PINNs or AdaI-PINNs (Roy et al., 2024). We propose the use of distinct neural networks for the field variables and material properties within each material, utilizing adaptive activation functions. While the neural networks across different materials share the same weights and biases, their activation functions are uniquely tailored using a hyperparameter that influences the slope of the activation function. The proposed framework is tested on several one-dimensional and two-dimensional benchmark examples, and its performance is compared with conventional PINNs and existing domain-decomposition PINNs frameworks, namely, the Multi-domain physics-informed neural network (M-PINN), and the eXtended physics-informed neural networks (XPINNs). The results demonstrate that the proposed approach can determine randomly distributed discontinuous material properties with an L 2 error of $\mathscr{O}$ (10 -3 ) for the material property and the root-mean-square error of $\mathscr{O}$ (10 -3 ) for the primary variable while the other approaches yield errors that are approximately two orders of magnitude larger (that is, $\mathscr{O}$ (10 -1 )). Moreover, the spatial distribution of material properties obtained using the proposed framework is in close agreement with the true distribution, whereas the other approaches fare much worse. Additionally, the proposed approach is approximately 40% faster than its competitors, indicating its potential as a robust alternative for solving inverse problems in heterogeneous materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Experimental and theoretical determinations of hydrogen isotopic equilibrium in the system CH 4 —H 2 —H 2 O from 3 to 200°C

The stable isotopic composition of methane (CH 4 ) is commonly used to fingerprint natural gas origins. Over the past 50 years, there have been numerous proposals that both microbial and thermogenic CH 4 can form in or later attain hydrogen isotopic equilibrium with water (H 2 O) and carbon isotopic equilibrium with carbon dioxide (CO 2 ). Evaluation of such proposals requires knowledge of the equilibrium fractionation factors between CH 4 and H 2 O or CO 2 at the temperatures where microbial and thermogenic CH 4 form in or are found in the environment, which is generally less than 200°C. Experimental determinations of these fractionation factors are only available above 200°C, requiring extrapolation of these results beyond the calibrated range or the use of theoretical calculations at lower temperatures. Here, we provide a calibration of the equilibrium hydrogen isotopic fractionation factor for CH 4 and hydrogen gas (H 2 ) ( D α CH4(g)–H2(g) ) based on experiments using γ-Al 2 O 3 and Ni catalysts from 3 to 200°C. Results were regressed as a 2 nd order polynomial of 1000 × ln D α CH4(g)–H2(g) vs. 1/T (K -1 ) yielding: 1000 × l n D α C H 4 ( g ) - H 2 ( g ) = 3.5317 × 10 7 T 2 + 2.7749 × 10 5 T - 179.48 We combine this calibration with previous experimental determinations of hydrogen isotope equilibrium between H 2 , H 2 O(g), and H 2 O(l) and we provide an interpolatable experimental calibration of 1000 × ln D α CH4(g)–H2O(l) from 3 to 200°C. Our resulting 4th order polynomial is the following equation: 1000 × l n D α C H 4 ( g ) - H 2 O l = - 7.9443 × 10 12 T 4 + 8.7772 × 10 10 T 3 - 3.4973 × 10 8 T 2 + 5.4398 × 10 5 T - 382.05 At 3°C, the value from our calibration differs by 93‰ relative to what would be calculated based on the extrapolation of the only experimental calibration currently available to temperatures below its calibrated range (lowest temperature of 200°C; Horibe and Craig, 1995). We additionally provide new theoretical estimates of hydrogen isotopic equilibrium between CH 4 (g), H 2 (g), and H 2 O(g) and carbon isotopic equilibrium between CH 4 (g) and CO 2 (g) using Path Integral Monte Carlo (PIMC) calculations. Our PIMC calculations for hydrogen isotopic equilibrium between CH 4 and H 2 agree 1:1 with our experiments. Finally, we compile carbon and hydrogen isotopic measurements of CH 4 , CO 2 , and H 2 O from various environmental systems and compare observed differences between carbon and hydrogen isotopes to those expected based on isotopic equilibrium. We find that isotopic compositions of some microbial gases from marine sedimentary, coalbed, and shale environments are consistent with those expected for CH 4 H 2 O(l) hydrogen and CH 4 CO 2 carbon isotopic equilibrium. In contrast, microbial terrestrial and pure culture gases are not consistent with both CH 4 H 2 O(l) hydrogen and CH 4 CO 2 carbon isotopic equilibrium. Overall, these results are explained qualitatively using previously developed conceptual models that link free energy gradients available to microorganisms to the degree that their enzymes can promote isotope-exchange reactions between CH 4 , CO 2 , and H 2 O.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Determination of the enthalpy of adsorption of hydrogen in activated carbon at room temperature

The development of high-performance materials for hydrogen storage by adsorption requires detailed understanding of the adsorbate-adsorbent interactions, e.g., the enthalpy of adsorption ΔH, which measures the interaction strength. The determination of ΔH for a weakly adsorbing gas such as hydrogen in a carbonaceous porous material is difficult experimentally, normally requiring measuring two cryogenic adsorption isotherms. Here we demonstrate a calculation of ΔH based on ca. room temperature adsorption isotherms at 273 K and 296 K using the Clausius-Clapeyron equation. This requires an estimation of the volume of the adsorbed film (~40%, ~12% of the total pore volume at 77 K, 296 K, respectively) obtained from fits of the excess adsorption isotherms to an Ono-Kondo model with the auxiliary use of a fixed point corresponding to the saturation film density (estimated as 100 ± 20 g/L) which appears to be remarkably sample and temperature independent, i.e., a property of the adsorbate. The calculated room temperature enthalpy of adsorption ΔH = 8.3 ± 0.4 kJ/mol is in excellent agreement with the low-coverage cryogenic determination of ΔH. The methodology hereby proposed facilitates reliable calculations of the enthalpy of adsorption at room temperatures for weakly-adsorbing gases.

08 HYDROGEN↗
DOE OSTI2024

Parametric optimization of the liquid sampling-atmospheric pressure glow discharge ionization source coupled to an Orbitrap mass spectrometer for neodymium isotope ratio determinations

Isotope ratio determinations are a valuable tool in several application areas. In nuclear forensics, the isotope ratios of uranium and plutonium are commonly used as a signature for the nuclear material's provenance and processing history. However, signatures from other coexisting elements, such as neodymium and samarium, can offer additional insights. Here, the liquid sampling-atmospheric pressure glow discharge (LS-APGD) ionization source coupled to an Orbitrap mass spectrometer (MS) has demonstrated its utility for actinide measurements. This instrumental platform can leverage the high resolution offered by the Orbitrap MS to overcome potential isobaric interferences, such as 144 Nd- 144 Sm, 148 Nd- 148 Sm, and 150 Nd- 150 Sm pairs. The work presented herein demonstrates the rapid, accurate, and precise determination of the isotope ratios for neodymium using the LS-APGD/Orbitrap MS. Both the LS-APGD and Orbitrap MS parameters were optimized systematically, with NdO + found to be the most abundant, most reduced species after applying the optimal collision-induced dissociation modalities. A limit of detection of 3 pg of 142 Nd was achieved when data was acquired and processed using the FTMS Booster, an external data acquisition and processing system offered by Spectroswiss. Excellent accuracy of better than 99 % and precision of <1 % RSD were achieved when a solution of the well-characterized neodymium standard (JNdi-1 standard) was analyzed under the optimized condition, indicating the LS-APGD/Orbitrap's great potential for isotope ratio analysis of Nd and other REEs for diverse applications.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Determination of permeability for hydrocarbon release due to excavation-induced stress redistribution in rock salt

Due to a stress redistribution after the excavation of an underground tunnel for radioactive waste disposal, an Ed/DZ (excavation disturbed/damaged zone) will be generated in the near field of the opening, resulting in significant changes in the hydraulic and mechanical properties of the rock mass in the zone. Initially more or less randomly distributed hydrocarbons at grain boundaries in rock salt, which sometimes can only be observed with ultraviolet light, can then be mobilised and migrate at a potentially significant rate towards the excavation. Within the international cooperative project DECOVALEX 2019, the migration mechanism of such fluid inclusions in rock salt is being studied intensively. Specifically, a multi-scale modelling strategy has been developed. A macroscale coupled hydro-mechanical modelling of an underground excavation was performed to determine hydraulic and time-dependent deviatoric stress conditions, by taking into account the rock salt creep behaviour. Under the obtained macro-scale constraints, micro-scale modelling of a pathway dilation along halite grain boundaries was performed using different model strategies: a) coupled hydromechanical modelling with a consideration of hydraulic pressure-induced dilatant deformation, b) nonlinear dynamic model taking account of fluid migration, stress-dependent grain boundary wetting and shear-induced dilatancy of salt, and c) phase-field modelling of flow pathway propagation. The permeability increase resulting from the pathway dilation is estimated to be as high as two orders of magnitude. Based on the permeability determined, a series of pressure buildups measured from a borehole with a high hydrocarbon release rate, a total of 430 build-ups within a monitoring time of 938 days, can be simulated with a macro-scale compressible flow model accounting for different zones around the opening.

58 GEOSCIENCES↗