Ne Isotopes Research Articles

Analysis of reaction cross sections of Ne and Mg isotopes at 240 MeV/u in the Dirac-Brueckner approach and Glauber model

Within a relativistic effective complex nucleon-nucleon interaction derived by solving the Dirac-Brueckner-Bethe-Goldstone equation, locally, starting from the one-boson-exchange potential (OBEP) as a bare NN interaction, the optical potentials and reaction cross sections of the 20-36Ne , 24-38Mg + 12C reactions, recently observed at 240MeV/u , are calculated. The proton and neutron density distributions of target and projectile are derived from Skyrme-Hartree-Fock calculations, employing SKRA and SKM* interactions. A comparison between the experimental data as well as recent theoretical calculations of Horiuchi et al. (Phys. Rev. C 86, 024614 (2012)) and Panda et al. (Mod. Phys. Lett. A 29, 1450013 (2014)) show that the data are well reproduced by the present relativistic calculations.

Identification of anomalous optical magnetic resonances in the total emission of a mixture of neon isotopes

In the dependence of the emission of a glow discharge in a mixture of isotopes 20Ne and 22Ne on the longitudinal magnetic-field strength, we have revealed narrow resonances, while the waves have non-Lorentzian shapes and are shifted with respect to zero field. Variations in the concentration of isotopes and discharge current can vary the amplitude, the shape, and the number of resonances; however, the position of each of them on the scale of the magnetic field almost does not depend on the spectral composition of the registered emission. We have elucidated a relation between the positions of the resonances on the scale of the magnetic field and the isotope shifts of neon transitions.

Fractionation of Ne and Ar isotopes by molecular diffusion in water

Molecular diffusion in water is a physical transport mechanism that plays an important role in many environmental processes. As the abundances of the chemically inert noble gases and their isotopes are controlled only by physical processes, they are ideal tracers for gas transfer processes in aquatic systems. Molecular diffusion in water is often thought to cause the mass-dependent fractionation of noble gas isotope ratios, e.g. 20Ne/22Ne and 36Ar/40Ar, under the assumption that the isotopic fractionation of gases in water can be adequately described in terms of a “square root relation”, i.e. in terms of the reciprocal of the square root of the ratio of their atomic masses. To quantify reliably the fractionation of 20Ne/22Ne and 36Ar/40Ar we determined the change in the isotope ratios of Ne and Ar after they had diffused through immobilised water. The Ne isotope fractionation factor, expressed as the ratio of the diffusion coefficients of 20Ne and 22Ne, was found to be D20Ne/D22Ne=1.010±0.003, which is considerably lower than that predicted from the square root relation, but close to results obtained from recent molecular dynamics calculations. In contrast to this, the Ar isotopic fractionation factor was found to be D36Ar/D40Ar=1.055±0.004, agreeing with that predicted from the square root relation. Thus, neither the square root relation nor calculations based on molecular dynamics are capable of giving a general explanation of the isotopic fractionation of both Ne and Ar that results when these gases undergo molecular diffusion through water. Our experimental results do not rely on a theoretical model and are considered to provide an accurate and robust quantification of the isotopic fractionation of Ne and Ar isotopes induced by molecular diffusion through water.

Helium isotope systematics in the vicinity of the Azores triple junction: Constraints on the Azores geodynamics

We present new He isotopic data from subaerial and submarine samples collected along the Terceira Rift (Azores Plateau) in order to constrain the sources involved in the Azores magmatism in the unique geodynamic context of the Azores triple junction. Lower than MORB 4He/3He isotopic ratios were determined on olivines from the Terceira Island and the adjacent Serreta submarine ridge (down to ≈69,000; ≈10.5 R/Ra), which in addition to the Ne isotopes previously published in Madureira et al. (2005) [Primitive helium and neon isotopes in Terceira Island: Constraints on the origin of the Azores archipelago. Earth and Planetary Science Letters 233, 429–440], support the geochemical models that consider the involvement of the lower mantle in the Azores magmatism. The analysis of He data published for the Mid-Atlantic Ridge (MAR) points to the existence of chemically distinct mantle domains underneath Eurasia and Nubia lithospheric plates, which can result from an heterogeneous distribution of asthenosphere metasomatism during the initial stages of plume activity in the Azores region. At the Terceira Rift, lavas from Graciosa Island, as well as from the western end of São Miguel Island and D. João de Castro Bank, display 4He/3He ratios similar to those observed along the MAR segments located to the north of the Azores triple junction area. Conversely, samples from the south Hirondelle Basin and also Faial display a He isotopic signature similar to that of MORB erupted along MAR segments located to the south of the Azores Plateau. The Terceira Rift and the Azores triple junction area are thus characterized by the mingling of two different asthenospheric domains referred as “Eurasia” and “Nubia” type and by the presence of mantle plume derived material having primitive helium signature.

Nuclear structure and reaction properties ofNe,MgandSiisotopes with RMF densities

We have studied nuclear structure and reaction properties of Ne , Mg and Si isotopes, using relativistic mean field (RMF) densities, in the framework of Glauber model. Total reaction cross-section σRfor Ne isotopes on12C target have been calculated at incident energy 240 MeV. The results are compared with the experimental data and with the recent theoretical study [W. Horiuchi et al., Phys. Rev. C 86, 024614 (2012)]. Study of σRusing deformed densities have shown a good agreement with the data. We have also predicted total reaction cross-section σRfor Ne , Mg and Si isotopes as projectiles and12C as target at different incident energies.

Microscopic mean field approximation and beyond with the Gogny force

Fully consistent axially-symmetric-deformed quasiparticle random phase approximation calculations have been performed with the D1S Gogny force. A brief review on the main results obtained in this approach is presented. After a reminder on the method and on the first results concerning giant resonances in deformed Mg and Si isotopes, the multipole responses up to octupole in the deformed and heavy nucleus 238U are discussed. In order to analyse soft dipole modes in exotic nuclei, the dipole responses have been studied in Ne isotopes and in N=16 isotopes, for which results are presented. In these nuclei, the QRPA results on the low lying 2+ states are compared to the 5-Dimensional Collective Hamiltonian ones. © Owned by the authors, published by EDP Sciences, 2014.

Search for halo nucleus in Mg isotopes through the measurements of reaction cross sections towards the vicinity of neutron drip line

Reaction cross sections ( R) for 24 38 Mg on C targets at the energies of around 240 MeV/ nucleon have been measured precisely at RIBF, RIKEN for the purpose of obtaining the crucial information on the changes of nuclear structure in unstable nuclei, especially around the so-called of region. In the island of inversion region, which includes neutron-rich Ne, Na, and Mg isotopes, the vanishing of the N = 20 magic number for neutrons have been discussed along with nuclear deformation. The present result suggest deformation features of Mg isotopes and shows a large cross section of weakly-bound nucleus 37 Mg, which could be caused by a neutron halo formation.

Effect of Tensor Force on the Halo Structure of 29Ne and 31Ne

The structure of Ne isotopes has been investigated by using deformed Skyrme—Hartree—Fock (SHF) method and BCS approximation. Especially the effect of tensor force on the halo structure of 29Ne and 31Ne is discussed. To this end, the tensor contributions are considered to the energy density function and the single particle potential in SHF theory. For comparison, four Skyrme interactions are used: SLy5 and SGII without tensor force, and SLy5+T and SGII+T with tensor force. The results indicate that the inclusion of tensor force shows a more pronounced halo structure for 31Ne.

Reaction dynamics and nuclear structure of moderately neutron-rich Ne isotopes by heavy ion reactions

The heavy ion reaction 22 Ne+208 Pb at 128 MeV of bombarding energy has been studied using the PRISMA-CLARA experimental setup at Legnaro National Laboratories. Elastic, inelastic and one nucleon transfer cross sections have been measured. The experimental results are presented in parallel with the analysis on existing data for the unstable 24 Ne nucleus, from the reaction 24 Ne+208 Pb at 182 MeV (measured at SPIRAL with the VAMOS-EXOGAM setup). The β 2 C charge deformation parameter for both 22 Ne and 24 Ne has been determined by a DWBA analysis of the experimental angular dis- tributions, showing a strong reduction for 24 Ne.

Mass-number and isotope dependence of local microscopic optical potentials for polarized proton scattering

We derive local microscopic optical potentials $U$ systematically for polarized proton scattering at 65~MeV using the local-potential version of the Melbourne $g$-matrix folding model. As target nuclei, we take $^{6}$He and neutron-rich Ne isotopes in addition to stable nuclei of mass number $A=4$--$208$ in order to clarify mass-number and isotope dependence of $U$. The local potentials reproduce the experimental data systematically and have geometries similar to the phenomenological optical potentials for stable targets. The target density is broadened by the weak-binding nature and/or deformation of unstable nuclei. For the real spin-orbit part of $U$ the density broadening weakens the strength and enlarges the radius, whereas for the central part it enlarges both of the strength and the radius. The density-broadening effect is conspicuous for halo nuclei such as $^{6}$He and $^{31}$Ne. Similar discussions are made briefly for proton scattering at 200~MeV. We briefly investigate how the isovector and the non spherical components of $U$ affect proton scattering.

Heterogeneities from the first 100 million years recorded in deep mantle noble gases from the Northern Lau Back-arc Basin

Heavy noble gases can record long-lasting heterogeneities in the mantle, because Ne, Ar, and Xe isotopes are produced from extant (U, Th, K) and extinct (129I and 244Pu) radionuclides. However, the presence of ubiquitous atmospheric contamination in basalts, particularly for ocean island basalts (OIBs) that sample the Earth's deep mantle, have largely hampered precise characterization of the mantle source compositions. Here we present new high-precision noble gas data from gas-rich basalts erupted along the Rochambeau Rift (RR) in the northwestern corner of the Lau Basin. The strong influence of a deep mantle plume in the Rochambeau source is apparent from low 4He/3He ratios down to 25,600 (3He/4He of 28.1RA).We find that the Rochambeau source is characterized by low ratios of radiogenic to non-radiogenic nuclides of Ne, Ar, and Xe (i.e., low 21Ne/22Ne, 40Ar/36Ar, and 129Xe/130Xe) compared to the mantle source of mid-ocean ridge basalts (MORBs). High-precision xenon isotopic measurements indicate that the lower 129Xe/130Xe ratios in the Rochambeau source cannot be explained solely by mixing atmospheric xenon with MORB-type xenon; nor can fission-produced Xe be added to MORB Xe to produce the compositions seen in the Rochambeau basalts. Deconvolution of fissiogenic xenon isotopes demonstrate a higher proportion of Pu- fission derived Xe in the Rochambeau source compared to the MORB source. Therefore, both I/Xe and Pu/Xe ratios are different between OIB and MORB sources. Our observations require heterogeneous volatile accretion and a lower degree of processing for the plume source compared to the MORB source. Since differences in 129Xe/130Xe ratios have to be produced while 129I is still alive, OIB and MORB sources must have been processed at different rates for the first 100 million years (Myr) of Solar System history, and subsequent to this period, the two reservoirs have not been homogenized.In combination with recent results from the Iceland plume, our noble gas observations require the formation and preservation of less-degassed, early-formed (pre-4.45Ga) heterogeneities in the Earth's deep mantle. Consequently, the primitive noble gas reservoir sampled by mantle plumes cannot be created solely through sequestration of recycled slabs or undegassed melts at the base of the mantle during the past 4.4Ga. Finally, if the more primitive, less degassed heterogeneities reside in the Large Low Shear Wave Velocity Provinces (LLSVPs), then LLSVPs must be long-lasting features of the deep mantle and are not composed exclusively of recycled material.

Tensor correlation, pairing interaction, and deformation in Ne isotopes and Ne hypernuclei

We study tensor and pairing effects on the quadruple deformation of neon isotopes based on a deformed Skyrme-Hartree-Fock model with BCS approximation for the pairing channel. We extend the Skyrme-Hartree-Fock formalism for the description of single- and double-$\ensuremath{\Lambda}$ hypernuclei adopting two different hyperon-nucleon interactions. It is found that the interplay of pairing and tensor interactions is crucial to derive the deformations in several neon isotopes. Especially, the shapes of ${}^{26,30}$Ne are studied in details in comparisons with experimentally observed shapes. Furthermore the deformations of the hypernuclei are compared with the corresponding neon isotopic cores in the presence of tensor force. We find the same shapes with somewhat smaller deformations for single $\ensuremath{\Lambda}$-hypernuclei compared with their core deformations. It is also pointed out that the latest version of hyperon interaction, the ESC08b model, having a deeper $\ensuremath{\Lambda}$ potential makes smaller deformations for hypernuclei than those of another NSC97f model.

Neon Isotope and Lambda Hypernuclei with the Nijmegen Hyperon Interaction

We optimize the nuclear parameterization for the description of Ne isotope in the deformed Skyrme–Hartree–Fock model, and succeed in providing an overall good description of the nuclear deformation in this model, which is consistent with the available experimental data and microscopic model results. The addition of a Λ hyperon, based on a realistic Nijmegen hyperon–nucleon potential, is found to have no large effect on the shape of the isotopic nuclei, indicating that the neon isotopic nuclei might not be good candidates for studying the deformation effect of hyperon in future experiments.

Direct molecular dynamics simulation of liquid-solid phase equilibria for a three-component plasma

The neutron-rich isotope ²²Ne may be a significant impurity in carbon and oxygen white dwarfs and could impact how the stars freeze. We perform molecular dynamics simulations to determine the influence of ²²Ne in carbon-oxygen-neon systems on liquid-solid phase equilibria. Both liquid and solid phases are present simultaneously in our simulation volumes. We identify liquid, solid, and interface regions in our simulations using a bond angle metric. In general we find good agreement for the composition of liquid and solid phases between our MD simulations and the semianalytic model of Medin and Cumming. The trace presence of a third component, neon, does not appear to strongly impact the chemical separation found previously for two-component carbon and oxygen systems. This suggests that small amounts of ²²Ne may not qualitatively change how the material in white dwarf stars freezes. However, we do find systematically lower melting temperatures (higher Γ) in our MD simulations compared to the semianalytic model. This difference seems to grow with impurity parameter Q_{imp} and suggests a problem with simple corrections to the linear mixing rule for the free energy of multicomponent solid mixtures that is used in the semianalytic model.

Effects of the electron correlation and Breit and hyperfine interactions on the lifetime of the2p53sstates in neutral neon

In the framework of the multiconfiguration Dirac-Hartree-Fock method, we investigate the transition properties of four excited states in the $2p^53s$ configuration of neutral neon. The electron correlation effects are taken into account systematically by using the active space approach. The effect of higher-order correlation on fine structures is shown. We also study the influence of the Breit interaction and find that it reduces the oscillator strength of the $^3P^o_1 - ^1S_0$ transition by 17%. It turns out that the inclusion of the Breit interaction is essential even for such a light atomic system. Our ab initio calculated line strengths, oscillator strengths and transition rates are compared with other theoretical values and experimental measurements. Good agreement is found except for the $^3P^o_2 - ^1S_0$ M2 transition for which discrepancies of around 15% between theories and experiments remain. In addition, the impact of hyperfine interactions on the lifetimes of the $^3P^o_0$ and $^3P^o_2$ metastable states is investigated for the $^{21}$Ne isotope (I=3/2). We find that hyperfine interactions reduce the lifetimes drastically. For the $^3P^o_0$ state the lifetime is decreased by a factor of 630.

Ab-initio multi-configuration Dirac-Hartree-Fock calculation on the lifetimes of levels in 2p53s configuration of neutral neon

Large-scale calculations have been performed using the GRASP2K package to accurately determine the lifetime of levels in 2p53s configuration of neutral neon. In particular, we calculated the hyperfine-induced transition rates from two metastable levels 3P20,0 to the ground state for odd Ne isotopes. It was found that hyperfine interactions drastically quench the lifetime of these two levels.

ISOTOPIC MASS FRACTIONATION OF SOLAR WIND: EVIDENCE FROM FAST AND SLOW SOLAR WIND COLLECTED BY THEGENESISMISSION

NASA's Genesis space mission returned samples of solar wind collected over ~2.3 years. We present elemental and isotopic compositions of He, Ne, and Ar analyzed in diamond-like carbon targets from the slow and fast solar wind collectors to investigate isotopic fractionation processes during solar wind formation. The solar wind provides information on the isotopic composition for most volatile elements for the solar atmosphere, the bulk Sun and hence, on the solar nebula from which it formed 4.6 Ga ago. Our data reveal a heavy isotope depletion in the slow solar wind compared to the fast wind composition by 63.1 ± 2.1‰ for He, 4.2 ± 0.5‰ amu–1 for Ne and 2.6 ± 0.5‰ amu–1 for Ar. The three Ne isotopes suggest that isotopic fractionation processes between fast and slow solar wind are mass dependent. The He/H ratios of the collected slow and fast solar wind samples are 0.0344 and 0.0406, respectively. The inefficient Coulomb drag model reproduces the measured isotopic fractionation between fast and slow wind. Therefore, we apply this model to infer the photospheric isotopic composition of He, Ne, and Ar from our solar wind data. We also compare the isotopic composition of oxygen and nitrogen measured in the solar wind with values of early solar system condensates, probably representing solar nebula composition. We interpret the differences between these samples as being due to isotopic fractionation during solar wind formation. For both elements, the magnitude and sign of the observed differences are in good agreement with the values predicted by the inefficient Coulomb drag model.

A global rain of micrometeorites following breakup of the L‐chondrite parent body—Evidence from solar wind‐implanted Ne in fossil extraterrestrial chromite grains from China

Abstract– Previous studies of limestone beds of mid‐Ordovician age from both Sweden and China show that the Earth saw an at least two orders of magnitude increase in the influx of extraterrestrial material approximately 470 Ma, following the disruption of an L‐chondrite parent body in the asteroid belt. Recovered extraterrestrial material consists of fossil meteorites and sediment‐dispersed extraterrestrial chromite (SEC) grains, both with L‐chondritic origin. Ne isotope analysis of SEC grains from one of the Swedish limestone sections revealed that the vast majority of the grains were delivered to Earth as micrometeorites. In this study, we extend the previous work, both in time and geographically, by measuring concentrations and isotopic ratios of Ne in individual SEC grains (60–120 μm in diameter) from three different beds from a contemporary Middle Ordovician limestone section in China. All of the Chinese SEC grains, 44 in total, contain surface‐implanted Ne of fractionated solar wind composition, implying that these grains were, as in the case of the Swedish SEC grains, delivered to Earth as micrometeorites. This gives further compelling evidence that the two to three orders of magnitude increase in the influx of micrometeoritic material following the breakup of the L‐chondrite parent body was indeed a global event. The rain of micrometeorites prevailed for at least 2 Myr (the estimated time of the deposition of the topmost Chinese bed) after the breakup event.

Giant Mesozoic gold provinces related to the destruction of the North China craton

Lode gold deposits in Precambrian cratons represent the world's major gold source and were mostly generated during formation and stabilization of the cratons. However, there is an extraordinary exception in the North China craton (NCC), where lode gold deposits formed after prolonged stabilization of the craton. Molybdenite Re–Os and hydrothermal sericite and biotite 40Ar/39Ar dating of major gold deposits from the Xiaoqinling district, southern NCC, bracket their emplacement in the range of 154.1±1.1 to 118.9±1.2Ma (n=23), postdating formation of the craton by more than 1.7 billion years. Fluid inclusions extracted from gold-bearing pyrite have elevated 3He/4He ratios (1.52–0.22Ra) and mantle-like Ne isotopes (20Ne/22Ne=10.02−9.22 and 21Ne/22Ne=0.033−0.027), indicating presence of mantle-derived fluids in the ore system. Measured δ34S of pyrite and δD and δ18O of hydrothermal micas and fluid inclusion waters in auriferous quartz further confirm a magmatic/mantle source for sulfur and ore fluids. Gold deposits of similar ages also widely occur in the eastern and northern margins of the NCC, which, together with those in the Xiaoqinling district, have a total reserve of ∼2500t gold, forming the only known giant late Mesozoic gold province in the world's Precambrian cratons. These deposits formed coevally with extensive felsic to mafic magmatism, development of intracontinental rift basins, and exhumation of metamorphic core complexes across the eastern NCC, events interpreted as indicating thinning and destruction of the lithosphere beneath the craton. Rising of asthenosphere coupled with destruction of the lithosphere has generated voluminous mafic and felsic magmas that provided sufficient fluids, sulfur and, by inference, other ore components to form the giant gold provinces.

Reaction dynamics and nuclear structure of moderately neutron-rich Ne isotopes by heavy-ion reactions

The heavy-ion reaction 22Ne+208Pb at 128 MeV beam energy has been studied using the PRISMA-CLARA experimental setup at Legnaro National Laboratories. Elastic, inelastic, and one-nucleon transfer differential cross sections are measured and global agreement is obtained with semiclassical and distorted-wave Born approximation (DWBA) calculations. In particular, the angular distribution of the 2+ state of 22Ne is analyzed by DWBA and a similar calculation is performed for the unstable 24Ne nucleus, using existing data from the reaction 24Ne+208Pb at 182 MeV (measured at SPIRAL with the VAMOS-EXOGAM setup). In both cases the DWBA model gives a good reproduction of the experiment, pointing to a strong reduction of the β2C charge deformation parameter in 24Ne. This follows the trend predicted for the evolution of the quadrupole deformation along the Ne isotopic chain.Received 8 May 2012DOI:https://doi.org/10.1103/PhysRevC.85.064621©2012 American Physical Society