Isotopes Of Heavy Elements Research Articles

Slow Neutron-Capture Process: Low-Mass Asymptotic Giant Branch Stars and Presolar Silicon Carbide Grains

Presolar grains are microscopic dust grains that formed in the stellar winds or explosions of ancient stars that died before the formation of the solar system. The majority (~90% in number) of presolar silicon carbide (SiC) grains, including types mainstream (MS), Y, and Z, came from low-mass C-rich asymptotic giant branch (AGB) stars, which is supported by the ubiquitous presence of SiC dust observed in the circumstellar envelope of AGB stars and the signatures of slow neutron-capture process preserved in these grains. Here, we review the status of isotope studies of presolar AGB SiC grains with an emphasis on heavy element isotopes and highlight the importance of presolar grain studies for nuclear astrophysics. We discuss the sensitives of different types of nuclei to varying AGB stellar parameters and how their abundances in presolar AGB SiC grains can be used to provide independent, detailed constraints on stellar parameters, including 13C formation, stellar temperature, and nuclear reaction rates.

Unlocking the Single-Crystal Record of Heavy Stable Isotopes

Stable isotopes provide deep insights into processes across a wide range of scales, from micron- to cosmic-size systems. Here, we review how continued advances in mass-spectrometry have enabled the analysis of ever-smaller samples and brought the field of heavy stable isotope geochemistry to its next frontier: the single-crystal scale. Accessing this record can be as enlightening as it is challenging. Drawing on novel systematics at different stages of development (from well-established to nascent), we discuss how the isotopes of heavy elements, such as magnesium, iron, zirconium, or uranium, can be used at the single-crystal and subcrystal scales to reconstruct magma thermal histories, crystal growth timescales, or, possibly, magma redox conditions.

Magnetic-buoyancy-induced Mixing in AGB Stars: Presolar SiC Grains

Abstract Isotope ratios can be measured in presolar SiC grains from ancient asymptotic giant branch (AGB) stars at permil-level (0.1%) precision. Such precise grain data permit derivation of more stringent constraints and calibrations on mixing efficiency in AGB models than traditional spectroscopic observations. In this paper we compare SiC heavy-element isotope ratios to a new series of FRUITY models that include the effects of mixing triggered by magnetic fields. Based on 2D and 3D simulations available in the literature, we propose a new formulation, upon which the general features of mixing induced by magnetic fields can be derived. The efficiency of such a mixing, on the other hand, relies on physical quantities whose values are poorly constrained. We present here our calibration by comparing our model results with the heavy-element isotope data of presolar SiC grains from AGB stars. We demonstrate that the isotopic compositions of all measured elements (Ni, Sr, Zr, Mo, Ba) can be simultaneously fitted by adopting a single magnetic field configuration in our new FRUITY models.

Mass-independent fractionation of titanium isotopes and its cosmochemical implications

Isotopes of heavy elements are produced in various amounts by nuclear processes in stars(1,2). Consequently, the presence of isotopic anomalies in the Solar System is considered to reflect the presence of presolar grains condensed in previous generations of stars(3) and not a (proto-) Solar System process. However, for oxygen, the major rock-forming element, it has been shown that physico-chemical reactions applicable to the presolar cloud or the protoplanetary disk were a possible source of isotopic variations due to mass-independent isotopic fractionation (MIF)(4,5). Here we show that MIF effects are not restricted to oxygen, but can also be produced for titanium. Titanium-rich grains experimentally condensed from a TiCl4(g)/C5H12(g) plasma exhibit MIF effects from -25% to +120% for all Ti isotopic ratios. These large Ti isotopic variations follow the model developed for oxygen MIF6 and mimic the Ti isotopic anomalies observed in some presolar grains. This effect is ascribed to the reactions between chemically indistinguishable isotopes(6) and could contribute to the complexity of isotopic anomalies observed in Solar System materials(1,7-14).

New results for laser isotope separation using low-energy methods

Today, research aimed at the development of low-energy methods of molecular laser isotope separation (MLIS) is relevant and in demand. The main goal of these studies is to find efficient and cost-effective methods that can be used as the basis for the technology of laser separation of uranium isotopes, as well as other elements. To date, a number of approaches to the implementation of low-energy methods of MLIS using infrared (IR) lasers have been proposed. Many of these approaches are not well understood and/or are difficult to put into practice. Some of them are considered to be promising and require further study. These include the method of isotope-selective suppression of the clustering of molecules using IR lasers during gas-dynamic expansion at a nozzle exit and the method of isotope-selective IR dissociation of small molecular van der Waals clusters. A review of recent results obtained using these two methods is presented. The experimental facilities and research methods are briefly described, and the choice of the objects of study is substantiated. Results obtained with model SF6 and CF3Br molecules are analyzed with reference to studying the process of isotope-selective suppression of the clustering of molecules among themselves and with atoms of an argon carrier gas, as well as the process of isotope-selective IR dissociation of small homogeneous and mixed clusters of (SF6)mArn and (CF3Br) m Arn (where m = 1 – 2 and 0 ⩽ n ⩽ 5 are the numbers of molecules and atoms in the clusters, respectively). The results presented suggest that these methods can be used for the separation of isotopes in molecules containing isotopes of heavy elements, which have a slight isotopic shift in the IR absorption spectra.

Synthesis of Transuranium Nuclei in Multinucleon Transfer Reactions at Near-Barrier Energies

In this paper we analyze production of various isotopes of heavy elements in reactions $$^{{48}}$$Ca, $$^{{136}}$$Xe, $$^{{238}}$$U + $$^{{251}}$$Cf. The analysis has been performed within a dynamical model based on the Langevin equations. The influence of the projectile on yields of heavy reaction products is discussed in the paper.

Infrared laser-induced isotope-selective dissociation of mixed (CF3Br)mArn van der Waals clusters

The paper presents the results of studies of IR laser-induced bromine-isotope-selective dissociation of small mixed (CF3Br)mArn van der Waals clusters (m = 1, 2 and 1 ≤ n ≤ 5 is the number of molecules and atoms in the clusters, respectively). The experiments used a pulsed CO2 laser to excite clusters and a quadrupole mass spectrometer to detect a molecular cluster beam. The research method is based on the selective vibrational excitation of clusters by IR laser radiation, leading to their predissociation. The possibilities of implementing bromine-isotope-selective dissociation of clusters are considered. The experimental setup and research method are briefly described. The results of determining the cluster dissociation efficiency and selectivity as functions of the energy and frequency of laser radiation are presented. It is shown that resonant vibrational excitation of clusters makes it possible to induce their isotope-selective dissociation. Thus, using a CF3Br/Ar mixture with a pressure ratio of 1/200, the enrichment factors of the 79Br isotope are found to be Kenr(79Br) = 1.15 ± 0.04 and 0.95 ± 0.03 under cluster irradiation conditions on the 9R(30) (ν = 1084.635 cm−1) and 9R(24) (ν = 1081.087 cm−1) lines, respectively The achieved dissociation selectivities for the clusters are, respectively, 1.16 ± 0.05 and 0.95 ± 0.04. The results obtained suggest that this method can be used to separate isotopes in molecules containing isotopes of heavy elements, which have a slight isotopic shift in the IR absorption spectra.

IR Laser Control of the Clustering of CF3Br Molecules during the Gas-Dynamic Expansion of a CF3Br/Ar Mixture: Bromine Isotope Selectivity

The infrared (IR) laser radiation control of the clustering of CF3Br molecules during the gas-dynamic expansion of a CF3Br/Ar mixture at the exit from a nozzle is investigated. Prominence is given to studying the possibility of bromine-isotope-selective suppression of the clustering of CF3Br molecules due to their resonance vibrational excitation in the gas-dynamic expansion zone near the nozzle. A continuous CO2 laser is used in experiments to excite molecules and clusters in a beam, and a quadrupole mass spectrometer is used to detect them. The experimental setup and the experimental technique are described. The dependences of the efficiency of molecule clustering suppression on the exciting laser radiation parameters, the gas parameters (composition, pressure) above the nozzle, and the distance from the nozzle exit section to a molecule irradiation zone are obtained. Bromine-isotope-selective suppression of molecule clustering is shown to occur at the exit from the nozzle due to the resonance vibrational excitation of gas-dynamically cooled CF3Br molecules. When CF3Br/Ar mixtures are used at pressure ratios p(CF3Br): p(Ar) = 1: 10 and 1: 30, the enrichment of a cluster beam by bromine isotopes are Kenr(81Br) ≈ 1.18 ± 0.09 and 1.12 ± 0.07 during the 9R(30) laser line (1084.635 cm–1) irradiation of a jet. The clustering suppression selectivity is α ≈ 1.18 when the mixture at the pressure ratio p(CF3Br): p(Ar) = 1: 10 is used. These results suggest that the proposed method can selectively control the clustering of the molecules containing the heavy element isotopes that have a small isotope shift in IR absorption spectra (OsO4, WF6, UF6).

Suppression of clustering of CF3Br molecules with argon atoms by CO2 laser radiation in gas-dynamic expansion of a CF3Br–Ar mixture: bromine isotope selectivity

We present the study of suppressing the clustering of CF3Br molecules with argon atoms under gas-dynamic expansion of the CF3Br–Ar mixture at a nozzle exit by a cw CO2 laser. The main attention is paid to the analysis of possibility of implementing the selective control of bromine isotope clustering. The method relies on the vibrational excitation of molecules with the laser radiation, which leads to the suppression of their clustering with argon atoms. The experimental setup and the method of study are briefly described. The results of evaluation of the efficiency and selectivity of suppression of molecular–atomic clustering for different compositions of the gas above the nozzle and separations between the irradiation zone and the nozzle exit section are presented. It is shown that under the resonance vibrational excitation of gas-dynamically cooled CF3Br molecules at the nozzle exit one can implement bromine isotope selective suppression of clustering of molecules with argon atoms. It is found that by controlling the clustering of CF3Br molecules with argon atoms one can implement considerably higher enrichment and selectivity factors than in the case of controlling the clustering of CF3Br molecules with each other. Thus, using the CF3Br–Ar mixture (the ratio of pressures 1 : 100 and 1 : 200) the enrichment factors for the bromine isotopes Kenr(81Br) = 1.50 ± 0.13 and 1.30 ± 0.09, respectively, were obtained under the conditions of irradiating the jet at the 9R(30) line of the laser (ν = 1084.635 cm−1). The selectivity α of the suppression of clustering of CF3Br molecules with argon atoms, achieved in this case, amounted to 4.02 ± 0.19 and 2.31 ± 0.11, respectively. The results show that the method allows one to selectively control the clustering of molecules, comprising isotopes of heavy elements that possess a small isotopic shift in the IR absorption spectra.

Use of compound-specific nitrogen isotope analysis of amino acids in trophic ecology: assumptions, applications, and implications

Knowledge of the diet source and trophic position of organisms is fundamental in food web science. Since the 1980s, stable isotopes of light elements such as 13C and 15N have provided unique information on the food web structure in a variety of ecosystems. More recently, novel isotope tools such as stable isotopes of heavy elements, radioisotopes, and compound-specific isotope analysis, have been examined by researchers. Here I reviewed the use of compound-specific nitrogen isotope analysis of amino acids (CSIA-AA) as a useful dietary tracer in food web ecology. Its three key features—(1) offsetting against isotopic variation; (2) universality of the trophic discrimination factor; and (3) sensitivity to source mixing—were compared with conventional isotope analysis for the bulk tissue of organisms. These three advantages of CSIA-AA will allow future researchers to (1) estimate the integrated trophic position (iTP) of animal communities; (2) infer trophic transfer efficiency (TTE) in food webs; and (3) quantify contributions from different resources to animals, all of which are crucial for understanding the relationship between biodiversity and multi-trophic ecosystem functioning. Further development of trophic ecology will be facilitated by both methodological refinement of CSIA-AA and its application to a wider range of organisms, food webs, and ecosystems.

Brome isotope selective control of CF3Br molecule clustering by IR laser radiation in gas-dynamic expansion of CF3Br – Ar mixture

We report the results of research on the experimental control of CF3Br molecule clustering under gas-dynamic expansion of the CF3Br – Ar mixture at a nozzle exit by using IR laser radiation. A cw CO2 laser is used for exciting molecules and clusters in the beam and a time-of-flight mass-spectrometer with laser UV ionisation of particles for their detection. The parameters of the gas above the nozzle are determined (compositions and pressure) at which intensive molecule clustering occurs. It is found that in the case of the CF3Br gas without carrier when the pressure P0 above the nozzle does not exceed 4 atm, molecular clusters actually are not generated in the beam. If the gas mixture of CF3Br with argon is used at a pressure ratio 1 : N, where N ⩾ 3, and the total pressure above the nozzle is P0 ⩾ 2 atm, then there occurs molecule clustering. We study the dependences of the efficiency of suppressing the molecule clustering on parameters of the exciting pulse, gas parameters above the nozzle, and on a distance of the molecule irradiation zone from the nozzle exit section. It is shown that in the case of resonant vibrational excitation of gas-dynamically cooled CF3Br molecules at the nozzle exit one can realise isotope-selective suppression of molecule clustering with respect to bromine isotopes. With the CF3Br – Ar mixtures having the pressure ratio 1 : 3 and 1 : 15, the enrichment factors obtained with respect to bromine isotopes are kenr ≈ 1.05 ± 0.005 and kenr ≈ 1.06 ± 0.007, respectively, under jet irradiation by laser emission in the 9R(30) line (1084.635 cm−1). The results obtained let us assume that this method can be used to control clustering of molecules comprising heavy element isotopes, which have a small isotopic shift in IR absorption spectra.

Nuclear field shift effects on stable isotope fractionation: a review

An anomalous isotope effect exists in many heavy element isotope systems (e.g., Sr, Gd, Zn, U). This effect used to be called the “odd–even isotope effect” because the odd mass number isotopes behave differently from the even mass number isotopes. This mass-independent isotope fractionation driving force, which originates from the difference in the ground-state electronic energies caused by differences in nuclear size and shape, is currently denoted as the nuclear field shift effect (NFSE). It is found that the NFSE can drive isotope fractionation of some heavy elements (e.g., Hg, Tl, U) to an astonishing degree, far more than the magnitude caused by the conventional mass-dependent effect (MDE). For light elements, the MDE is the dominant factor in isotope fractionation, while the NFSE is neglectable. Furthermore, the MDE and the NFSE both decrease as temperatures increase, though at different rates. The MDE decreases rapidly with a factor of 1/T2, while the NFSE decreases slowly with a factor of 1/T. As a result, even at high temperatures, the NFSE is still significant for many heavy element isotope systems. In this review paper, we begin with an introduction of the basic concept of the NSFE, including its history and recent progress, and follow with the potential implications of the inclusion of the NFSE into the kinetic isotope fractionation effect (KIE) and heavy isotope geochronology.

Rovibrational effects on NMR shieldings in a heavy-element system: XeF2

Fully quantum-mechanical treatment of the effects of thermal rovibrational motion in a heavy-element molecule with relativistic effects is carried out for the heavy (129/131)Xe and light (19)F nuclear shieldings in the linear XeF(2) molecule. More importantly, purely quantum-mechanical, intramolecular phenomena, the primary and secondary isotope effect on these shieldings, respectively, are treated with including both the zero-point vibrational and finite-temperature effects. While large solvent effects influence the experimental absolute shielding constants and chemical shifts (thereby making comparison of experiment and theory very difficult), they are not significant for the isotope shifts. We study the role of electron correlation at both nonrelativistic (NR) and relativistic [Breit-Pauli perturbational theory (BPPT) as well as 4-component Dirac theory] level. We obtain quantitative agreement with the nearly solvent-independent experimental (19)F secondary isotope shifts. This implies a promising accuracy for our predictions of the experimentally so far non-existing primary Xe isotope shift and the temperature dependence of Xe and F chemical shifts corresponding to a low pressure gas phase. To achieve this, a combination of high-level ab initio NR shielding surface is found necessary, in the present work supplemented by relativistic corrections by density-functional theory (DFT). Large errors are demonstrated to arise due to DFT in the NR shielding surface, explaining findings in recent computational studies of heavy-element isotope shifts. Besides a high-quality property hypersurface, the inclusion of thermal effects (in addition to zero-point motion) is also necessary to compare with experimental results. The geometry dependence of the different relativistic influences on the wave function, Zeeman interaction, and hyperfine interaction, as well as their role in the temperature dependence of both the Xe and F shielding constants and their isotope shifts, are discussed. The relativistic rovibrational effects arise from the same individual contributions as previously found for the chemical shifts and shielding anisotropies. In general, the spin-orbit interactions are more sensitive to rovibrational motion than the scalar relativistic contributions. A previously suggested third-order BPPT contribution to shielding anisotropy is shown to be important for a better agreement with experiment.

Determination of the Geographic Origin of Rice by Chemometrics with Strontium and Lead Isotope Ratios and Multielement Concentrations

The objective of this study was to develop a technique for determining the country of origin of rice in the Japanese market. The rice samples included a total of 350 products grown in Japan (n = 200), the United States (n = 50), China (n = 50), and Thailand (n = 50). In this study, (87)Sr/(86)Sr and Pb isotope ((204)Pb, (206)Pb, (207)Pb, and (208)Pb) ratios and multielement concentrations (Al, Fe, Co, Ni, Cu, Rb, Sr, and Ba) were determined by high-resolution inductively coupled plasma mass spectrometry. By combining three chemometric techniques based on different principles and determination criteria, the countries of origin of rice were determined. The predictions made by 10-fold cross-validation were around 97% accurate. The presented method demonstrated the effectiveness of determining the geographic origin of an agricultural product by combining several chemometric techniques using heavy element isotope ratios and multielement concentrations.

The chemical evolution of globular clusters - II. Metals and fluorine

In the first paper of this series, we proposed a new framework in which to model the chemical evolution of globular clusters. This model is predicated upon the assumption that clusters form within an interstellar medium enriched locally by the ejecta of a single Type Ia supernova and varying numbers of asymptotic giant branch stars, superimposed on an ambient medium pre-enriched by low-metallicity Type II supernovae. Paper I was concerned with the application of this model to the observed abundances of several reactive elements and so-called non-metals for three classical intermediate-metallicity clusters, with the hallmark of the work being the successful recovery of many of their well-known elemental and isotopic abundance anomalies. Here, we expand upon our initial analysis by (i) applying the model to a much broader range of metallicities (from the factor of 3 explored in Paper I, to now a factor of ∼50; i.e. essentially, the full range of Galactic globular cluster abundances; and (ii) incorporating a broader suite of chemical species, including a number of iron-peak isotopes, heavier α-elements and fluorine. While allowing for an appropriate fine-tuning of the model input parameters, most empirical globular cluster abundance trends are reproduced; our model would suggest the need for a higher production of calcium, silicon and copper in low-metallicity (or so-called ‘prompt’) Type Ia supernovae than predicted in current stellar models in order to reproduce the observed trends in NGC 6752, and a factor of 2 reduction in carbon production from asymptotic giant branch stars to explain the observed trends between carbon and nitrogen. Observations of heavy-element isotopes produced primarily by Type Ia supernovae, including those of titanium, iron and nickel, could support/refute unequivocally our proposed framework, although currently the feasibility of the proposed observations is well beyond current instrumental capabilities. Hydrodynamical simulations would be necessary to study its viability from a dynamical point of view.

Nuclear half-lives for α-radioactivity of elements with 100 ⩽ Z ⩽ 130

Theoretical estimates for the half-lives of about 1700 isotopes of heavy elements with 100 ⩽ Z ⩽ 130 are tabulated using theoretical Q-values. The quantum mechanical tunneling probabilities are calculated within a WKB framework using microscopic nuclear potentials. The microscopic nucleus–nucleus potentials are obtained by folding the densities of interacting nuclei with a density-dependent M3Y effective nucleon–nucleon interaction. The α-decay half-lives calculated in this formalism using the experimental Q-values were found to be in good agreement over a wide range of experimental data spanning about 20 orders of magnitude. The theoretical Q-values used for the present calculations are extracted from three different mass estimates viz. Myers–Swiatecki, Muntian–Hofmann–Patyk–Sobiczewski, and Koura–Tachibana–Uno–Yamada.

Predictions of alpha decay half lives of heavy and superheavy elements

Theoretical estimates for the lifetimes of several isotopes of heavy elements with Z = 102 – 120 are presented by calculating the quantum mechanical tunneling probability in a WKB framework and using microscopic nucleus–nucleus potential obtained by folding the densities of interacting nuclei with the DDM3Y effective nuclear interaction. The α-decay half lives calculated in this formalism using the experimental Q-values are in good agreement over a wide range of experimental data. Half lives are also calculated using Q-values extracted from two mass formulae. The Viola–Seaborg–Sobiczewski (VSS) estimates of α-decay half lives with the same Q-values are presented for comparison. The half life calculations are found to be quite sensitive to the choice of Q-values. Comparison with the experimental data delineates the inadequacies of older mass predictions in the domain of heavy and superheavy elements as compared to the newer one by Muntian–Hofmann–Patyk–Sobiczewski, and highlights necessity of a more accurate mass formula which can predict Q-values with even higher precision.

On the bulk isotopic composition of magnesium and silicon during the May 1998 CME: ACE/SWIMS

The coronal mass ejection (CME) observed at the Advanced Composition Explorer (ACE) spacecraft on May 2 and 3, 1998, exhibited very high as well as exceptionally low charge states of all ions. In addition, ³He was considerably enhanced by in the bulk material of the CME. High ³He/4He ratios in solar energetic particles have recently been observed in some events to coincide with substantial enrichments in the heavy isotopes of heavy elements. We use data from the Solar Wind Ion Mass Spectrometer (SWIMS) on ACE to investigate whether the enrichment of the heavy isotopes in solar energetic particles is mirrored in the isotopic composition of solar wind Mg and Si. We concentrate on the time period where the unusual mixture of charge states and unusually high ³He/4He was observed to test for isotopic fractionation in such extreme solar wind conditions. We find very little or no enrichment of the neutron‐rich isotopes with respect to the main isotopes. Incidentally, this is also the first report on the isotopic composition of ions with Z > 2 in the bulk material in a CME.

The Application of Highly Accurate Laboratory Wavelengths to Abundance and Isotope Measurements in B Stars

The relative positions of absorption lines in stellar spectra observed at high dispersion and high signal-to-noise with the Hubble Space Telescope's Goddard High Resolution Spectrograph (HST/GHRS) can often be measured with a precision of about 0.001 Å. Similar capabilities are expected from the Space Telescope Imaging Spectrograph (STIS). Under what circumstances do such astronomical data justify the acquisition of laboratory data with comparable accuracy?We will review a number of our GHRS spectra of B stars where such laboratory data have been critical to achieving our scientific goals. Studies of isotope ratios are one case where precision wavelengths are essential, and we will discuss our work on heavy element isotope anomalies in the HgMn stars χ Lupi and HR 7775, as well as work on boron isotope ratios in early-B stars. In some cases the interpretation and even the identification of an individual absorption feature can be critically influenced by the laboratory data.

Frontiers of heavy element nuclear and radiochemistry

The production and half-lives of the heaviest chemical elements, now known through Z=112, are reviewed. Recent experimental evidence for the stabilization of heavy element isotopes due to proximity to deformed nuclear shells at Z=108 andN=162 is compared with the theoretical predictions. The possible existence of isotopes of elements 107–110 with half-lives of seconds or longer, and production reactions and experimental techniques for increasing the overall yields of such isotopes in order to study both their nuclear and chemical properties are discussed. The present status of studies of the chemical properties of Rf, Ha, and Sg is briefly summarized and prospects for extending chemical studies beyond Sg are considered.