Hydrogen Isotope Labeling of Pharmaceuticals Via Dual Hydrogen Isotope Exchange Pathways Using CdS Quantum Dot Photocatalyst
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Maity, Rajendra↗
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Results for “isotope”
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Titanium and chromium isotopic compositions of calcium-aluminum-rich inclusions: Implications for the sources of isotopic anomalies and the formation of distinct isotopic reservoirs in the early Solar System
As the earliest-dated solids in our Solar System, calcium-aluminum-rich inclusions (CAIs) provide a record of their formation environment near the young Sun and hold clues to the formation of planetary-scale isotopic reservoirs in the solar protoplanetary disk. Although CAIs from several CV, CK, CM, CO, and ordinary chondrites have been analyzed previously for their Ti isotopic compositions, CAIs from just three CV chondrites have been analyzed for their Cr isotopic compositions, and only a handful of CAIs have been measured for both their Ti and Cr isotopic compositions. We report mass-independent Ti and Cr isotopic anomalies in several CAIs from CV and CK chondrites; this is the first report of the Cr isotopic composition of a CAI from a CK chondrite. With this data, we aim to better constrain the compositional range of CAIs in ε 50 Ti versus ε 54 Cr space, thereby facilitating the isotopic characterization of the material inherited by the solar protoplanetary disk and the role of CAIs in the formation of distinct planetary-scale isotopic reservoirs in our early Solar System. The narrow range in isotopic anomalies in CAIs when compared to other early-formed refractory inclusions such as platy hibonite crystals (PLACs) and spinel-hibonite inclusions (SHIBs) suggests that CAIs record the mixing of these precursor materials and the averaging of their larger isotopic anomalies. The isotopic composition of CAIs is therefore likely the result of a combination of factors, including mixing of material inherited from their formation region, heterogeneous carrier phase distribution, and thermal processing in the disk. The ε 50 Ti and ε 54 Cr isotopic compositions of CAIs are not correlated, further demonstrating that these isotopic anomalies have different carrier phases. The Ti and Cr isotopic compositions of CAIs additionally show that CAIs alone cannot be responsible for the compositional difference between the non-carbonaceous chondritic (NC) and carbonaceous chondritic (CC) isotopic reservoirs but nevertheless do play a role in the formation of these large-scale isotopic reservoirs in the early Solar System.
58 GEOSCIENCES↗
Hydrogen isotope fractionation in the system brucite-water ± NaCl to elevated temperatures and pressures: Implications for the isotopic property of NaCl fluids under geologic conditions
According to the article, a series of hydrothermal experiments have been conducted to determine equilibrium D/H fractionations between brucite and water as a function of temperature (200-600 °C), pressure (2.1-800 MPa), and dissolved NaCl (0-5 molal or 0-22.6 wt%). Along with our previous study, a total of 39 data points show that pressure and dissolved NaCl both increase the D/H fractionation factor at a given temperature. Theoretical treatment allowed a first direct comparison of experimental and theoretical results of brucite-water D/H fractionation at a zero pressure limit. After correcting the pressure effects on brucite D/H partition function ratios (β-factor), the isotope effects of pressure and dissolved NaCl on the D/H β-factor of water were for the first time rigorously evaluated. There is a good linear relationship between the D/H β-factor of the aqueous NaCl solutions and their densities of at a given temperature. A good, pseudo-linear relationship observed between the density of aqueous NaCl solutions and the maximum intensity of the asymmetric OH vibrational frequency of water in turn suggests that this frequency is a fundamental property that determines the β-factor of water at elevated temperatures and pressures. Our study suggests that the density of aqueous solutions (ρ aq-soln ) could be used as a primary parameter to predict the effects of pressure and NaCl compositions on the β-factor of water under geologic conditions encountered in the crust and upper mantle:Δ10 3 1n β wat /Δρ aq-soln = -0.0111 (±0.0012), where Δ is a difference in the value of 10 3 In β wat or ρ aq-soln , and ρ aq-soln in kg m -3 .
bio-inspired, mechanical behavior, carbon sequestr↗
Mercury Stable Isotope Fractionation During Coal Combustion in Coal-Fired Boilers: Reconciling Atmospheric Hg Isotope Observations with Hg Isotope Fractionation Theory
Mercury (Hg) stable isotope is a useful tool to understand the transformation of atmospheric Hg. The observation on the enrichment of heavier isotopes in gaseous elemental Hg (GEM) relative to oxidized Hg{sup II} species in atmosphere cannot be convincingly explained by isotope fractionation of Hg redox processes. This review shows that the large Hg isotope mass dependent fractionation (MDF) in coal-fired boilers is one of the underlying reasons. The reported Hg isotope data of feed coals and their combustion products are first summarized to give a general overview of how Hg isotopes fractionate before Hg discharge from coal-fired boilers. Then, predictive MDF models are discussed to simulate δ{sup 202}Hg values of different Hg species in coal combustion flue gases. The discharged GEM is predicted to have the highest δ{sup 202}Hg followed by gaseous Hg{sup II} and particulate-bound Hg{sup II}, which is in consistent with the observed MDF pattern of atmospheric Hg species.
54 ENVIRONMENTAL SCIENCES↗
Analogous intruder behavior near Ni, Sn, and Pb isotopes
Near shell closures, the presence of unexpected states at low energies provides a critical test of our understanding of the atomic nucleus. New measurements for the N = 42 isotones $69\atop{27}$Co and $71\atop{29}$Cu, along with recent data and calculations in the Ni isotopes, establish a full set of complementary, deformed, intruder states astride the closed-shell 28 Ni isotopes. In addition, nuclei with a one-proton hole or one-proton particle adjacent to Z = 28 were populated in β-decay experiments and in multinucleon transfer reactions. A β-decaying isomer, with a 750(250)-ms half-life, has been identified in $69\atop{27}$Co 42 . It likely has low spin and accompanies the previously established 7/2 - state. Complementary data for the levels of isotonic $71\atop{29}$Cu 42 support the presence of a deformed, ΔJ = 1 band built on the proton intruder 7/2 - level at 981 keV. Finally, these data, together with recent studies of lower-mass Co and Cu isotopes and extensive work near 68 Ni , support the view that intruder states based on particle-hole excitations accompany all closed proton shells with Z ≥ 28 .
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
High-precision γ -ray spectroscopy of the cardiac PET imaging isotope Rb 82 and its impact on dosimetry
82 Rb is a positron-emitting isotope used in cardiac positron emission tomography (PET) imaging which has been reported to deliver a significantly lower effective radiation dose than analogous imaging isotopes like 201 Tl and 99m Tc sestamibi. High-quality β-decay data are essential to accurately appraise the total dose received by the patients. A source of 82 Sr was produced at the Brookhaven Linac Isotope Producer (BLIP), transported to Argonne National Laboratory, and studied with the Gammasphere facility. Significant revisions have been made to the level scheme of 82 Kr including 12 new levels, 50 new γ-ray transitions, and the determination of many new spin assignments through angular correlations. Lastly, these new high-quality data allow a precise reappraisal of the β-decay strength function and thus the consequent dose received by patients.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Fast and efficient charge breeding of the Californium rare isotope breeder upgrade electron beam ion source
The Electron Beam Ion Source (EBIS), developed to breed Californium Rare Isotope Breeder Upgrade (CARIBU) radioactive beams at Argonne Tandem Linac Accelerator System (ATLAS), is being tested off-line. A unique property of the EBIS is a combination of short breeding times, high repetition rates, and a large acceptance. Overall, we have implemented many innovative features during the design and construction of the CARIBU EBIS as compared to the existing EBIS breeders. The off-line charge breeding tests are being performed using a surface ionization source that produces singly charged cesium ions. The main goal of the off-line commissioning is to demonstrate stable operation of the EBIS at a 10 Hz repetition rate and a breeding efficiency into single charge state higher than 15%. These goals have been successfully achieved and exceeded. We have measured (20% ± 0.7%) breeding efficiency into the single charge state of 28+ cesium ions with the breeding time of 28 ms. In general, the current CARIBU EBIS operational parameters can provide charge breeding of any ions in the full mass range of periodic table with high efficiency, short breeding times, and sufficiently low charge-to-mass ratio, 1/6.3 for the heaviest masses, for further acceleration in ATLAS. In this study, we discuss the parameters of the EBIS and the charge breeding results in a pulsed injection mode with repetition rates up to 10 Hz.
43 PARTICLE ACCELERATORS↗
Experimental determinations of carbon and hydrogen isotope fractionations and methane clumped isotope compositions associated with ethane pyrolysis from 550 to 600°C
Methane clumped isotope compositions signify the relative natural abundances of rare, doubly substituted isotopic species of methane ( 13 CH 3 D and 12 CH 2 D 2 ) and have emerged as a new isotopic tool to trace the sources, sinks, and lifecycles of methane in the environment. Such measurements can identify equilibration (or reequilibration) temperatures if found to be in isotopic equilibrium or non-equilibrium processes (e.g., kinetically controlled reactions or mixing) if not in isotopic equilibrium. Naturally occurring thermogenic methane—formed by the thermally activated breakdown of larger organic molecules—has been found to have clumped isotope compositions consistent with equilibrium at reasonable gas formation temperatures in some settings and non-equilibrium processes occurring during either formation, migration, storage, or extraction in others. To explore the potential controls on the isotopic composition of thermogenic methane, we conducted isothermal time-series ethane pyrolysis experiments at 550 and 600 °C to measure methane and ethane 13 C/ 12 C and D/H fractionations and methane clumped isotope compositions (resolved 13 CH 3 D and 12 CH 2 D 2 ). We explore the effects of modifying the initial clumped isotope composition of ethane and the addition of water vapor to pyrolysis experiments. We observe that ethane and methane 13 C/ 12 C are controlled by kinetic isotope effects and Rayleigh distillation processes. In contrast, ethane and methane D/H and methane clumped isotope compositions appear to be controlled by a combination of these processes and hydrogen isotope exchange. The hydrogen isotope exchange processes lead to isotopic equilibrium as reaction completion is approached for both D/H (ethane/methane) and methane clumped isotope compositions. Here, we develop a chemical model based on a mass balance approach that accounts for inheritance vs. hydrogen-abstraction formation pathways for singly and doubly substituted isotopologues of ethane and methane that is compared to the experimental data. The model allows the determination of carbon and hydrogen kinetic isotope effects associated with ethane cracking and hydrogen abstraction reactions that, where applicable, we compare to prior theoretical constraints. From the comparison of the model to the experimental data, we infer that the kinetically controlled ethane and methane bulk isotope compositions and methane clumped isotope compositions are controlled by kinetic isotope effects (both primary and secondary) associated with both C–C bond and C–H bond cleavage reactions. Specifically, the methane clumped isotope compositions likely result from a combination of clumped isotope effects associated with ethane breakdown and/or assembly of methane isotopologues (expressed in terms of γ-factor parameters ≠ 1) and combinatorial effects that arise probabilistically. We discuss our experimental results in the context of recent pyrolysis experiments and observations of naturally occurring thermogenic methane. We consider a proposal consistent with observations from nature that the hydrogen isotope exchange reactions that promote equilibration of methane isotopic molecules at or near formation temperature may be facilitated by free radicals generated by pyrolysis reactions. In this framework, isotope exchange effectively ceases when pyrolysis effectively ceases locking in compositions that can be consistent with peak formation temperatures.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Low temperature, non-stoichiometric oxygen-isotope exchange coupled to Fe(II)–goethite interactions
Not Available
Frierdich, Andrew J.↗
Stable-carbon isotope ratios for sourcing the nerve-agent precursor methylphosphonic dichloride and its products
The ability to connect a chemical threat agent to a specific batch of a synthetic precursor can provide a fingerprint to contribute to effective forensic investigations. Stable isotope analysis can leverage intrinsic, natural isotopic variability within the molecules of a threat agent to unlock embedded chemical fingerprints in the material. Methylphosphonic dichloride (DC) is a chemical precursor to the nerve agent sarin. It is converted to methylphosphonic difluoride (DF) as part of the sarin synthesis process. We used a suite of commercially available DC stocks to both evaluate the potential for δ13C analysis to be used as a fingerprinting tool in sarin-related investigations and to develop sample preparation techniques (using chemical hydrolysis) that can simplify isotopic analysis of DC and its synthetic products. We demonstrate that natural isotopic variability in DC results in at least three distinct, isotope-resolved clusters within the thirteen stocks we analyzed. Isotopic variability in the carbon feedstock (i.e., methanol) used for DC synthesis is likely inherited by the DC samples we measured. We demonstrate that the hydrolysis of DC and DF to methylphosphonic acid (MPA) can be used as a preparative step for isotopic analysis because the reaction does not impart a measureable isotopic fractionation. MPA is more chemically stable, less toxic, and easier to handle than DC or DF. Further, the hydrolysis method we demonstrated can be applied to a suite of other precursors or to sarin itself, thereby providing a potentially valuable forensic tool.
Moran, James J.↗
Investigating Stable Oxygen and Carbon Isotopic Variability in Speleothem Records Over the Last Millennium Using Multiple Isotope-Enabled Climate Models
The incorporation of water isotopologues into the hydrology of general circulation models (GCMs) facilitates the comparison between modeled and measured proxy data in paleoclimate archives. However, the variability and drivers of measured and modeled water isotopologues, as well as the diversity of their representation in different models, are not well constrained. Improving our understanding of this variability in past and present climates will help to better constrain future climate change projections and decrease their range of uncertainty. Speleothems are a precisely datable terrestrial paleoclimate archives and provide well-preserved (semi-)continuous multivariate isotope time series in the lower latitudes and mid-latitudes and are therefore well suited to assess climate and isotope variability on decadal and longer timescales. However, the relationships of speleothem oxygen and carbon isotopes to climate variables are influenced by site-specific parameters, and their comparison to GCMs is not always straightforward. Here we compare speleothem oxygen and carbon isotopic signatures from the Speleothem Isotopes Synthesis and Analysis database version 2 (SISALv2) to the output of five different water-isotope-enabled GCMs (ECHAM5-wiso, GISS-E2-R, iCESM, iHadCM3, and isoGSM) over the last millennium (850–1850 CE). We systematically evaluate differences and commonalities between the standardized model simulation outputs. The goal is to distinguish climatic drivers of variability for modeled isotopes and compare them to those of measured isotopes. We find strong regional differences in the oxygen isotope signatures between models that can partly be attributed to differences in modeled surface temperature. At low latitudes, precipitation amount is the dominant driver for stable water isotope variability; however, at cave locations the agreement between modeled temperature variability is higher than for precipitation variability. While modeled isotopic signatures at cave locations exhibited extreme events coinciding with changes in volcanic and solar forcing, such fingerprints are not apparent in the speleothem isotopes. This may be attributed to the lower temporal resolution of speleothem records compared to the events that are to be detected. Using spectral analysis, we can show that all models underestimate decadal and longer variability compared to speleothems (albeit to varying extents). We found that no model excels in all analyzed comparisons, although some perform better than the others in either mean or variability. Therefore, we advise a multi-model approach whenever comparing proxy data to modeled data. Considering karst and cave internal processes, e.g., through isotope-enabled karst models, may alter the variability in speleothem isotopes and play an important role in determining the most appropriate model. By exploring new ways of analyzing the relationship between the oxygen and carbon isotopes, their variability, and co-variability across timescales, we provide methods that may serve as a baseline for future studies with different models using, e.g., different isotopes, different climate archives, or different time periods.
isotope-enabled simulations↗
Image segmentation for uranium isotopic analysis by SIMS: Combined adaptive thresholding and marker controlled watershed approach
A novel approach to particle identification and particle isotope ratio determination has been developed for nuclear safeguard applications. This particle search approach combines an adaptive thresholding algorithm and marker-controlled watershed segmentation (MCWS) transform, which improves the secondary ion mass spectrometry (SIMS) isotopic analysis of uranium containing particle populations for nuclear safeguards applications. The Niblack assisted MCWS approach (a.k.a. SEEKER) developed for this work has improved the identification of isotopically unique uranium particles under conditions that have historically presented significant challenges for SIMS image data processing techniques. Particles obtained from five NIST uranium certified reference materials (CRM U129A, U015, U150, U500 and U850) were successfully identified in regions of SIMS image data 1) where a high variability in image intensity existed, 2) where particles were touching or were in close proximity to one another and/or 3) where the magnitude of ion signal for a given region was count limited. Analysis of the isotopic distributions of uranium containing particles identified by SEEKER showed four distinct, accurately identified 235U enrichment distributions, corresponding to the NIST certified 235U/238U isotope ratios for CRM U129A/U015 (not statistically differentiated), U150, U500 and U850. Additionally, comparison of the minor uranium isotope (234U, 235U and 236U) atom percent values verified that, even in the absence of high precision isotope ratio measurements, SEEKER could be used to segment isotopically unique uranium particles from SIMS image data. Although demonstrated specifically for SIMS analysis of uranium containing particles for nuclear safeguards, SEEKER has application in addressing a broad set of image processing challenges.
adaptive thresholding↗
Shape phase changes with N in 72-84 Kr isotopes
The Kr isotopes lying in between the lighter isotopes of (Zn, Ge, and Se) and the heavier isotopes of (Sr and Zr) in the A=70-80 region exhibit very interesting spectral features. The spectra of 72-84 Kr isotopes display a striking contrast from those of Zn, Ge and Se isotopes. The role of spherical and oblate and prolate deformed subshell gaps at specific Z and N and the resulting re-inforcement are strikingly evident in these contrasting features, with variation in Z or N. The evolution of the spectral features in Kr isotopes with N as reflected in the quadrupole deformation, K-band structures, E0 decay, B(E2) values, β-softness of the nuclear core, and odd–even staggering in K π = 2 + γ-bands is studied to explore the role of the under lying nuclear interactions. Further, the correlations with odd–A isotopes are explored. The shape co-existence displayed in some Kr isotopes is studied. The large deformation observed in the ground bands of 74,76 Kr, as exhibited in the B(E2) values is especially interesting.
74 ATOMIC AND MOLECULAR PHYSICS↗
Isotopic Effect on Electrochemical CO2 Reduction Activity and Selectivity in H2O- and D2O-based Electrolytes over Palladium
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99 GENERAL AND MISCELLANEOUS↗
Conclusions • Multimaterial and isotopically-labeled specimens were successfully fabricated via FFF-AM • Raman spectroscopy, atomic force microscopy, and neutron scattering show promise for direct measurements of interlayer diffusion in the multimaterial and isotopically-labeled specimens • Although isotopically-labeled specimens offer the greatest potential for experimentally verifying FFF-AM process models, substituting hydrogen with deuterium alters the thermal and rheological properties of the HDPE polymer
Multimaterial and Isotopically Labeled Specimen Fabrication via Material Extrusion Additive Manufacturing for Interlayer Diffusion Analysis
Jones, Haley W. [Savannah River National Laborator↗
Production of highly-enriched 134Ba for a reference material for isotope dilution mass spectrometry measurements
Isotope dilution mass spectrometry (IDMS) is an analytical technique capable of providing accurate and precise quantitation of trace isotope abundance and assay providing measurement uncertainties below 1 %. To achieve these low uncertainties, the IDMS method ideally utilizes chemically pure “spike” solutions that consist of a single highly enriched isotope that is well-characterized relating to the abundance of companion isotopes and concentration in solution. To address a current demand for accurate 137Cs/137Ba ratio measurements for “age” determination of radioactive 137Cs sources, Idaho National Laboratory (INL) is producing enriched 134Ba isotopes that are tobe used for IDMS spikes to accurately determine 137Ba accumulation from the decay of 137Cs. The final objective of this work it to provide a homogenous set of reference materials that the National Institute of Standards and Technology can certify as standard reference materials used for IDMS. The process that was developed at INL for the separation and isolation of Ba isotopes, chemical purification of the isotopes in solution, and the encapsulation of the materials will be described.
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
Natural isotopic compositions of titanium, iron, and nickel observed in commercial fuel pellets – Promising candidate elements for stable isotope tagging
Stable isotope taggants would constitute unique identifiers for nuclear fuel cycle materials, resulting in expedited timelines and high confidence provenance assessments for nuclear forensics investigations. However, reliably identifying and interpreting stable isotope taggants in nuclear materials recovered from outside of regulatory control will largely be predicated on the assumption that the taggant element intrinsic to the untagged nuclear material exhibits natural isotopic ratios. Here, we present high-precision Ti, Fe, and Ni isotope compositions in 13 commercial low-enriched uranium (LEU) fuel pellets to assess the suitability of these transition metals as stable isotope taggants. Our investigations reveal limited isotope variations among the fuel pellets in all three elements, which are consistent with small mass-dependent isotope fractionations, comparable to variations previously reported for natural samples. In practice, isotopically tagged nuclear materials are expected to fall along isotopic mixing lines, since intrinsic background levels of taggant elements dilute the taggant towards natural isotope compositions. Furthermore, the observation that Ti, Fe, and Ni isotope compositions in a suite of LEU fuel pellets are close to or indistinguishable from estimates for the Bulk Silicate Earth demonstrates that a two end-member mixing assumption would be valid for these transition metals, indicating that all three are promising candidate elements for stable isotope tagging. Finally, we present mass balance calculations to quantify isotopic perturbations expected from admixing isotopically anomalous Ti, Fe, and Ni taggants to assess the interplay between elemental and taggant concentrations and find favorable compromises for facilitating successful taggant identification with current analytical methods.
Intentional forensics↗