SEARCH · Engineering Papers
Results for “CALCIUM ISOTOPES”
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Proton superfluidity and charge radii in proton-rich calcium isotopes
We report that one of the most important global properties of the atomic nucleus is its size. Experimentally determined nuclear charge radii carry unique information on the nuclear force and complex dynamics of protons and neutrons moving inside the nucleus. The intricate behaviour of charge radii along the chain of Ca isotopes, including the unexpectedly large charge radius of neutron-rich 52 Ca, poses a daunting challenge for nuclear theory. Here we present the measurements of the charge radii of proton-rich isotopes 36,37,38 Ca, whose properties are impacted by the interplay between nuclear superfluidity and weak binding. Calculations carried out within nuclear density functional theory show that the combination of a novel interaction and a state-of-the-art theoretical method can successfully explain the behaviour of charge radii from the lightest to the heaviest Ca isotopes. Lastly, through this model, we show how the new data on 36,37,38 Ca elucidate the nature of nucleonic pairing in weakly bound proton-rich isotopes.
Emergence of low-energy monopole strength in the neutron-rich calcium isotopes
Not Available
Calcium Isotope Constraints on Recycled Carbonates in Subduction-related Magmas
Calcium isotope ratios are readily mass-fractionated by low-temperature depositional processes that can be recorded in sedimentary rocks and, therefore, have the potential to track distinct geochemical signatures of recycled materials in mantle-derived igneous rocks. In this study, I report calcium isotopic compositions for well-characterized lavas from the Central American volcanic arc that exhibit a range of trace element and radiogenic isotope signatures that have been used to indicate variable amounts of subducted marine carbonate and hemipelagic sedimentary rocks, fresh carbonatite lavas from Oldoinyo Lengai Volcano, Tanzania, and an intrusive carbonatite clast erupted 12.8 ka from the Laacher See Volcano, Germany. I observed no calcium isotope evidence for recycled sedimentary rocks in the Central American arc magmas or in the Oldoinyo Lengai carbonatite volcanic rocks. They all exhibit isotopic compositions similar to rocks dominated by a primitive, mantle-like, bulk silicate Earth (BSE) composition. The exception in this work is the calcium isotope composition measured in the intrusive Laacher See carbonatite that is resolvable from BSE (δ^44 Ca = 0.0). Although this calcium isotopic signature might be related to ancient carbonate recycling, the magnitude and relatively light calcium isotopic composition (δ^44 Ca = –0.4) of this carbonatite could also reflect an origin that involved partial melting of altered lithospheric mantle, from which isotopically heavy Ca-bearing fluids have been lost. The decoupled signatures between trace elements and their radiogenic isotopes and those recorded by calcium isotope data are important because they likely reflect different sources and processes, and demonstrate that sediment subduction is not a bulk mixing process.
Potassium and Calcium Isotopic Fractionation by Plants (Soybean [Glycine max], Rice [Oryza sativa], and Wheat [Triticum aestivum])
Here, we conducted hydroponic experiments growing soybean (Glycine max), rice (Oryza sativa), and wheat (Triticum aestivum) under K and Ca replete conditions to establish the degree of K isotopic fractionation by plants, and compare the isotopic fractionation of Ca and K. Each of the test plants displays fractionation relative to the growth solution favoring the light isotopes of K and Ca. The average δ 41 K values of the roots from the three plant species were similar, and have an overall average of -0.55 ± 0.24‰ 2s, while the overall average δ 44 Ca for roots is -0.67 ± 0.44. For leaves, the overall average of δ 41 K is -0.97 ± 0.4‰, compared to an overall average leaf δ 44 Ca of -0.83 ± 0.09‰. In the case of the soybean plants, the lightest K and Ca occurs in the stems with average δ 41 K of -1.31 ± 0.40‰ 2s and average δ 44 Ca of -1.20 ± 0.19 ‰ 2s. We present a simple box model involving the relative fluxes of K and its isotopic fractionation that reproduces our K isotopic observations and suggests a fractionation of ~0.8‰ with K uptake from solution by roots. Finally, directly comparing the per amu fractionation of K and Ca reveals an average factor of 2.05 ± 0.50 2s greater fractionation of K isotopes which may reflect their different roles and behaviors in plants.
Variations in Urine Calcium Isotope: Composition Reflect Changes in Bone Mineral Balance in Humans
Changes in bone mineral balance cause rapid and systematic changes in the calcium isotope composition of human urine. Urine from subjects in a 17 week bed rest study was analyzed for calcium isotopic composition. Comparison of isotopic data with measurements of bone mineral density and metabolic markers of bone metabolism indicates the calcium isotope composition of urine reflects changes in bone mineral balance. Urine calcium isotope composition probably is affected by both bone metabolism and renal processes. Calcium isotope. analysis of urine and other tissues may provide information on bone mineral balance that is in important respects better than that available from other techniques, and illustrates the usefulness of applying geochemical techniques to biomedical problems.
Neutron-rich calcium isotopes within realistic Gamow shell model calculations with continuum coupling
Based on the realistic nuclear force of the high-precision CD-Bonn potential, we have performed comprehensive calculations for neutron-rich calcium isotopes using the Gamow shell model (GSM) which includes resonance and continuum. The realistic GSM calculations produce well binding energies, one- and two-neutron separation energies, predicting that 57 Ca is the heaviest bound odd isotope and 70 Ca is the dripline nucleus. Resonant states are predicted, which provides useful information for future experiments on particle emissions in neutron-rich calcium isotopes. Shell evolutions in the calcium chain around neutron numbers $\textit{N}$ = 32, 34, and 40 are understood by calculating effective single-particle energies, the excitation energies of the first 2 + states and two-neutron separation energies. The calculations support shell closures at 52 Ca ($\textit{N}$ = 32) and 54 Ca ($\textit{N}$ = 34) but show a weakening of shell closure at 60 Ca ($\textit{N}$ = 40). Finally, the possible shell closure at 70 Ca ($\textit{N}$ = 50) is predicted.
Additive effects of acidification and mineralogy on calcium isotopes in Triassic/Jurassic boundary limestones
The end-Triassic mass extinction coincided with a negative δ 13 C excursion, consistent with release of 13 C-depleted CO 2 from the Central Atlantic Magmatic Province. However, the amount of carbon released and its effects on ocean chemistry are poorly constrained. The co upled nature of the carbon and calcium cycles allows calcium isotopes to be used for constraining carbon cycle dynamics and vice versa. We present a high-resolution calcium isotope (δ 44/40 Ca) record from 100 m of marine limestone spanning the Triassic/Jurassic boundary in two stratigraphic sections from northern Italy. Immediately above the extinction horizon and the associated negative excursion in δ 13 C, δ 44/40 Ca decreases by ca. 0.8‰ in 20 m of section and then recovers to preexcursion values. Coupled numerical models of the geological carbon and calcium cycles demonstrate that this δ 44/40 Ca excursion is too large to be explained by changes to seawater δ 44/40 Ca alone, regardless of CO 2 injection volume and duration. Less than 20% of the δ 44/40 Ca excursion can be attributed to acidification. The remaining 80% likely reflects a higher proportion of aragonite in the original sediment, based largely on high concentrations of Sr in the samples. Our study demonstrates that coupled models of the carbon and calcium cycles have the potential to help distinguish contributions of primary seawater isotopic changes from local or diagenetic effects on the δ 44/40 Ca of carbonate sediments. Finally, differentiating between these effects is critical for constraining the impact of ocean acidification during the end-Triassic mass extinction, as well as for interpreting other environmental events in the geologic past.
Structure of Neutron-rich Calcium Isotopes and Roles of Three-body Interaction
Structure of neutron-rich calcium isotopes are studied by shell model calculations with the inclusion of three-body interactions. The three-body force induces repulsive contributions to the monopole terms of the valence neutron-neutron interaction Ground state energies of the isotopes, which have deviations from the experimental values near drip-lines only with the microscopic two-body interaction, are found to be well reproduced up to the observed ones when the three-body interaction is included. The excitation energies of the 2{sub 1}{sup +} state in {sup 48}Ca and {sup 54}Ca are found to be enhanced with the inclusion of the three-body interaction. The three-body force thus plays a key role for the magicity of {sup 48}Ca and {sup 54}Ca. The magnetic dipole (M1) strength in {sup 48}Ca, which is fragmented in case with the microscopic two-body interaction only, is found to be concentrated and pushed up to higher excitation energy when the three-body interarction is included. An important role of the multipole components is pointed out for the concentration of the strength.
Calcium Isotope Separation in a Hot-Wall Plasma Centrifuge
We propose a method of calcium isotope sepration using a countercurrent plasma centrifuge with a hot wall, which separating the fractions by means of vapor deposition at the end faces of the device. The centrifugal force, providing the effect of radial separation, is excited due to acceleration of a weakly ionized calcium plasma by a rotating magnetic field, while the axial circulating flow, which increases the effect of radial separation, is created by a traveling magnetic field. The capabilities of the method are demonstrated by the example of calculation of the separation factor of the plasma centrifuge as a function of the parameter characterizing the circulation intensity.
Semiquantitative Estimates of Rainfall Variability During the 8.2 kyr Event in California Using Speleothem Calcium Isotope Ratios
A multiproxy record from a fast-growing stalagmite reveals variable hydroclimate on the California coast across the 8.2 kyr event and a precursor event likely caused by initial drainage of proglacial Lake Agassiz. Using speleothem δ 44 Ca, we develop the first semiquantitative estimates of paleorainfall variability for California through calibration with measurements of the modern climate and cave environment. We find that the magnitude of rainfall variability during the 8.2 kyr event approached the multiyear variability observable in the recent past (1950–2019) and the magnitude of variability during the precursor event likely exceeded this range. Additionally, we observe other instances of multidecadal variability comparable in magnitude to the precursor event during the record. Finally, our work suggests that speleothem calcium isotope ratios are a powerful semiquantitative means to reconstruct paleorainfall, although numerous factors must be assessed in each cave system before applying this approach.
The influence of seawater carbonate chemistry, mineralogy, and diagenesis on calcium isotope variations in Lower-Middle Triassic carbonate rocks
The geological calcium cycle is linked to the geological carbon cycle through the weathering and burial of carbonate rocks. As a result, calcium (Ca) isotope ratios ( 44 Ca/ 40 Ca, expressed as δ 44/40 Ca) can help to constrain ancient carbon cycle dynamics if Ca cycle behavior can be reconstructed. But, the δ 44/40 Ca of carbonate rocks is influenced not only by the δ 44/40 Ca of seawater but also by diagenetic processes and fractionation associated with carbonate precipitation. In this study, we investigate the dominant controls on carbonate δ 44/40 Ca in Upper Permian to Middle Triassic limestones (ca. 253 to 244 Ma) from south China and Turkey. This time interval is ideal for assessing controls on Ca isotope ratios in carbonate rocks because fluctuations in seawater δ 44/40 Ca may be expected based on several large carbon isotope (δ 13 C) excursions ranging from -2 to + 8‰. Parallel negative δ 13 C and δ 44/40 Ca excursions were previously identified across the end-Permian extinction horizon. Here, we find a second negative excursion in δ 44/40 Ca of ~ 0.2‰ within Lower Triassic strata in both south China and Turkey; however, this excursion is not synchronous between regions and thus cannot be interpreted to reflect secular change in the δ 44/40 Ca of global seawater. Additionally, δ 44/40 Ca values from Turkey are consistently 0.3‰ lower than contemporaneous samples from south China, providing further support for local or regional influences. By measuring δ 44/40 Ca and Sr concentrations ([Sr]) in two stratigraphic sections located at opposite margins of the Paleo-Tethys Ocean, we can determine whether the data represent global conditions (e.g., secular variations in the δ 44/40 Ca of seawater) versus local controls (e.g., original mineralogy or diagenetic alteration). The [Sr] and δ 44/40 Ca data from this study are best described statistically by a log-linear correlation that also exists in many previously published datasets of various geological ages. By using a model of early marine diagenetic water-rock interaction, we illustrate that this general correlation can be explained by the chemical evolution of bulk carbonate sediment samples with different initial mineralogical compositions that subsequently underwent recrystallization. Although early diagenetic resetting and carbonate mineralogy strongly influence the carbonate δ 44/40 Ca values, the relationship between [Sr] and δ 44/40 Ca holds potential for reconstructing first-order secular changes in seawater δ 44/40 Ca composition.
Shell-model study of calcium isotopes toward their drip line
Here, we report in this paper a study in terms of the nuclear shell model about the location of the calcium isotopes drip line. The starting point is considering the realistic two-body potential derived by Entem and Machleidt within chiral perturbation theory at next-to-next-to-next-to-leading order (N 3 LO), as well as a chiral three-body force at next-to-next-to-leading order (N 2 LO) whose structure and low-energy constants are consistent with the two-body potential. Then we construct the effective single-particle energies and residual interaction needed to diagonalize the shell-model Hamiltonian. The calculated two-neutron separation energies agree nicely with experiment until 56 Ca, which is the heaviest isotope whose mass has been measured, and do not show any sign of two-neutron emission until 70 Ca . We discuss the role of the choice of the model space in determining the neutron drip line, and also the dependence of the results on the parameters of the shell-model Hamiltonian.
Unexpectedly large charge radii of neutron-rich calcium isotopes
Here, despite being a complex many-body system, the atomic nucleus exhibits simple structures for certain ‘magic’ numbers of protons and neutrons. The calcium chain in particular is both unique and puzzling: evidence of doubly magic features are known in 40,48 Ca, and recently suggested in two radioactive isotopes, 52,54 Ca. Although many properties of experimentally known calcium isotopes have been successfully described by nuclear theory, it is still a challenge to predict the evolution of their charge radii. Here we present the first measurements of the charge radii of 49,51,52 Ca, obtained from laser spectroscopy experiments at ISOLDE, CERN. The experimental results are complemented by state-of-the-art theoretical calculations. The large and unexpected increase of the size of the neutron-rich calcium isotopes beyond N = 28 challenges the doubly magic nature of 52 Ca and opens new intriguing questions on the evolution of nuclear sizes away from stability, which are of importance for our understanding of neutron-rich atomic nuclei.
A Procedure to Determine the Coordinated Chromium and Calcium Isotopic Composition of Astromaterials Including the Chelyabinsk Meteorite
The isotopic compositions of elements are often used to characterize nucelosynthetic contributions in early Solar System objects. Coordinated multiple middle-mass elements with differing volatilities may provide information regarding the location of condensation of early Solar System solids. Here we detail new procedures that we have developed to make high-precision multi-isotope measurements of chromium and calcium using thermal ionization mass spectrometry, and characterize a suite of chondritic and terrestrial material including two fragments of the Chelyabinsk LL-chondrite.
Rapid CO 2 mineralisation into calcite at the CarbFix storage site quantified using calcium isotopes
The engineered removal of atmospheric CO 2 is now considered a key component of mitigating climate warming below 1.5 °C. Mineral carbonation is a potential negative emissions technique that, in the case of Iceland’s CarbFix experiment, precipitates dissolved CO 2 as carbonate minerals in basaltic groundwater settings. Here we use calcium (Ca) isotopes in both pre- and post-CO 2 injection waters to quantify the amount of carbonate precipitated, and hence CO 2 stored. Ca isotope ratios rapidly increase with the pH and calcite saturation state, indicating calcite precipitation. Calculations suggest that up to 93% of dissolved Ca is removed into calcite during certain phases of injection. In total, our results suggest that 165 ± 8.3 t CO 2 were precipitated into calcite, an overall carbon storage efficiency of 72 ± 5%. The success of this approach opens the potential for quantification of similar mineral carbonation efforts where drawdown rates cannot be estimated by other means.
Using Natural Stable Calcium Isotopes to Rapidly Assess Changes in Bone Mineral Balance Using a Bed Rest Model to Induce Bone Loss
Metabolic bone diseases like osteoporosis result from the disruption of normal bone mineral balance (BMB) resulting in bone loss. During spaceflight astronauts lose substantial bone. Bed rest provides an analog to simulate some of the effects of spaceflight; including bone and calcium loss and provides the opportunity to evaluate new methods to monitor BMB in healthy individuals undergoing environmentally induced-bone loss. Previous research showed that natural variations in the Ca isotope ratio occur because bone formation depletes soft tissue of light Ca isotopes while bone resorption releases that isotopically light Ca back into soft tissue (Skulan et al, 2007). Using a bed rest model, we demonstrate that the Ca isotope ratio of urine shifts in a direction consistent with bone loss after just 7 days of bed rest, long before detectable changes in bone mineral density (BMD) occur. The Ca isotope variations tracks changes observed in urinary N-teleopeptide, a bone resorption biomarker. Bone specific alkaline phosphatase, a bone formation biomarker, is unchanged. The established relationship between Ca isotopes and BMB can be used to quantitatively translate the changes in the Ca isotope ratio to changes in BMD using a simple mathematical model. This model predicts that subjects lost 0.25 0.07% ( SD) of their bone mass from day 7 to day 30 of bed rest. Given the rapid signal observed using Ca isotope measurements and the potential to quantitatively assess bone loss; this technique is well suited to study the short-term dynamics of bone metabolism.