Ne Isotopes Research Articles

Investigation on the deformation of Ne and Mg isotope chains within relativistic mean-field model

Ne and Mg isotope chains are investigated based on constrained calculations in the framework of a deformed relativistic mean-field (RMF) model with the NL075 parameter set. The calculated quadrupole deformation and binding energy are compared with other theoretical results as well as the available experimental data. It shows that the calculated deformations of Ne and Mg with the NL075 are more accurate than those obtained with the NL-SH. It is predicted that 19,29,32Ne and 20,31Mg maybe have a triaxial deformation and 25−28Ne and 27−30Mg exhibit a shape coexistence probably. The closure effect of neutron number N=8 for 20Mg is predicted to be very weak.

Search for neutron excitations across theN=20shell gap inNe25−29

Nuclear structure of the neutron rich Ne25−29 nuclei has been investigated through the in-beam γ-ray spectroscopy technique using fragmentation reactions of both stable and radioactive beams. Level schemes have been deduced for these Ne isotopes. In order to examine the importance of intruder fp configurations, they are compared to shell model calculations performed either in the restricted sd or in the larger sdpf valence space. The Ne25,26 and Ne27 nuclei were found to be in agreement with the sd shell model calculations, whereas Ne28 exhibits signatures of the intruder fp shell contribution.4 MoreReceived 27 October 2004DOI:https://doi.org/10.1103/PhysRevC.72.054316©2005 American Physical Society

Spectroscopy of Ne, Na and Mg isotopes approaching the Island of Inversion

A beam of 26Mg at 160 MeV incident on a thin target of 150Nd was used to initiate deep-inelastic and multi-nucleon transfer reactions. The gamma-decay of the fragments produced in the reaction was studied using the EUROBALL IV array of escape suppressed Ge detectors at Strasbourg combined with the binary reaction spectrometer used to detect the projectile-like fragments. Preliminary results from the experiment are presented.

Spectroscopy of Ne and Na isotopes: Preliminary results from a EUROBALL + Binary Reaction Spectrometer experiment

The gamma-decay of fragments from deep-inelastic and multi-nucleon transfer processes which occur when a beam of 26Mg at 160MeV is incident on a thin 150Nd target was studied using the EUROBALL IV array of escape suppressed Ge detectors at Strasbourg. The good resolving power of EUROBALL IV was further increased by combining it with the Binary Reaction Spectrometer (BRS), used for the detection of projectile-like fragments. The BRS allows full kinematic reconstruction of the binary reaction allowing crucial Doppler corrections of gamma-ray spectra to be performed. Some preliminary results are presented. -1

Deformations and electromagnetic moments of light exotic nuclei

Structure of carbon and neon isotopes is investigated by deformed Skyrme Hartree-Fock and shell model calculations. We point out that the quadrupole deformations of C and Ne isotopes have strong isotope dependence as a typical example of the evolution of deformations in nuclei. It is shown also that the quadrupole moments and the magnetic moments of the odd C isotopes depend clearly on assigned configurations, and their experimental data will be useful to determine the spin-parities and the deformations of the ground states of these nuclei. The electric quadrupole (E2) transitions in even C and Ne isotopes are also studied. The isotope dependence of the E2 transition strength is reproduced properly, although the calculated strength overestimates an extremely small observed value in 16C.

Cluster structure in stable and unstable nuclei

Cluster structure in stable and unstable nuclei has been studied. We report recent developments of theoretical studies on cluster aspect, which is essential for structure study of light unstable nuclei. We discuss negative parity bands in even-even Be and Ne isotopes and show the importance of cluster aspect. Three-body cluster structure and cluster crystallization are also introduced. It was found that the coexistence of cluster and mean-field aspect brings a variety of structures to unstable nuclei.

Deformations and electromagnetic moments in carbon and neon isotopes

Static and dynamic quadrupole moments of C and Ne isotopes are investigated by using the deformed Skyrme Hartree-Fock model and also shell model wave functions with isospin-dependent core polarization charges. We point out that the deformations of C and Ne isotopes have a strong isotope dependence as a manifestation of spontaneous symmetry breaking effect in nuclear physics. The effect of spontaneous symmetry breaking is a general phenomenon known in many fields of physics. It is shown at the same time that the quadrupole moments $Q$ and the magnetic moments $\ensuremath{\mu}$ of the odd C and odd Ne isotopes depend clearly on assigned configurations, and their experimental data will be useful to determine the deformations of the ground states of nuclei near the neutron drip line. Electric quadrupole $(E2)$ transitions in even C and Ne isotopes are also studied using the polarization charges obtained by the particle vibration coupling model with shell model wave functions. Although the observed isotope dependence of the $E2$ transition strength is reproduced properly in both C and Ne isotopes, the calculated strength overestimates an extremely small observed value in $^{16}\mathrm{C}$.

Electric dipole transitions in neutron-rich nuclei

The structure of neutron-rich nuclei in several isotopes is investigated by shell model calculations. We study the electric dipole (E1) transitions in C isotopes focusing on the interplay between the low-energy Pigmy strength and the giant dipole resonance (GDR). Reasonable agreement is obtained with available experimental data for the photoreaction cross sections in 12C, 13C, and 14C with the inclusion of the quenching effects. A low-energy peak in the dipole strength in 15C is associated with a single-particle motion of the 1s1/2 valence neutron relative to the 14C core. The calculated transition strength below the GDR in C isotopes heavier than 15C is found to exhaust about 50–80% of the cluster sum rule value and 12–16% of the classical Thomas-Reiche-Kuhn sum rule value. Next, we point out that the quadrupole and magnetic moments in the odd C isotopes strongly depend on configuration, which will be useful to determine the spin parities and the deformations of the ground states of these nuclei. The electric quadrupole (E2) transitions in even C isotopes are also studied. The isotopic dependence of the E2 transition strength is found to be reasonably well explained, although the calculated strength largely overestimates the unexpectedly small strength observed in 16C. The E1 strength in 18N and 19N as well as in Ne isotopes is also investigated.

Preliminary study on noble gas isotopes of mantle-derived peridotite xenoliths along the Tan-Lu Fault belt, Eastern China

In order to understand the nature of noble gas reservoirs beneath continents, elemental and isotopic compositions of noble gases were analyzed from spinel-lherzolites with anhydrous mineral assemblages (i.e., olivine+clinopyroxene+orthopyroxene +spinel±apatite±garnet); these are considered to be typical of the upper lithospheric mantle. Isotopic compositions of the noble gases were measured for peridotite xenoliths enclosed in Cenozoic alkaline basalts in eastern-central China to provide insight on mantle characteristics. The results show that the noble gas abundances and isotopic compositions in mantle-derived xenoliths from eastern-central China vary widely:4He abundances from 0.0024×10−6 to 25.0×10−6 (cm3stp/g);3He/4He ratios range between 0.33RA and 4.62 RA;40Ar/36Ar ratios from 250.56 to 1233.86;40Ar abundances from 0.97×10−6 to 34.18×10−6(cm3/g). Only three measured Ne isotopes show a degree of homogeneity:20Ne from 0.3 to 0.7 (cm3stp/g);20Ne/22Ne ratios from 10.5 to 11.0; and20Ne abundances are also rather uniform, from 35.8×10−13 to 47.8×10−13 (cm3stp/g), and129Xe/130Xe ratios from 6.50 to 6.70. It can be seen that3He/4He ratios vary largely, and40Ar/36Ar ratios are significantly lower than MORB and Proterozoic crust, but close to that of atmospheric values. On the basis of the noble gas abundances and isotope compositions, it can be concluded that Ne, Kr and Xe in mantle-derived xenoliths from NE China have atmospheric origin. The results also show the heterogeneity of noble gases in peridotite from the upper mantle in eastern China, which accords with the results of previous geochemical studies.

Evidence for subduction-related components in the subcontinental mantle from low 3He/ 4He and 40Ar/ 36Ar ratio in mantle xenoliths from Far Eastern Russia

By applying both vacuum crushing and stepwise heating methods for the extraction of the noble gases, we have discovered 3He/ 4He ratios much lower than the atmospheric ratio (∼0.3 R A; R A is the atmospheric 3He/ 4He ratio of 1.4×10 −6) and relatively low 40Ar/ 36Ar ratios (<1000) in olivine separates from some subcontinental mantle-derived xenoliths from Far Eastern Russia. The low 3He/ 4He ratios cannot be explained by the addition of radiogenic 4He generated in-situ after the eruption of magma entraining the xenoliths. Furthermore, petrographic evidence suggests that incorporation of crustal fluids is not likely. Hence, it must reflect a feature of the Far Eastern Russian upper mantle. Spectroscopic and petrographic observations confirm that there are at least two compositionally distinct fluids in these xenoliths; liquid CO 2 inclusions and melt inclusions with shrinkage bubbles. Based on the crushing experiments, it is inferred that the inclusions of liquid CO 2 have a 3He/ 4He ratio similar to that of MORB, and the component with the low 3He/ 4He ratio is derived from the shrinkage bubbles in the melt inclusions. For the present samples, the 40Ar/ 36Ar ratios obtained by crushing were less than 1000, suggesting incorporation of atmospheric components in the source materials. Since low 40Ar/ 36Ar ratios were observed irrespective of the occurrence of the liquid CO 2 inclusions, the atmospheric component exists in the melt inclusions. Ne and Xe isotopes are also consistent with incorporation of atmospheric components. Since the Far Eastern Russia area was located at a subduction zone in the Jurassic–early Cretaceous Period, it is most likely that the melt inclusions displaying atmospheric noble gas characteristics together with low 3He/ 4He ratios have been derived from the Jurassic–Cretaceous subducted slab. Although we cannot exclude the possibility that low 3He/ 4He ratios are due to the existence of minor U-bearing minerals in the lithospheric continental mantle caused by metasomatism, we have no petrographical evidence for such minerals in this area. On the other hand, 3He/ 4He ratios observed in the liquid CO 2 inclusions, which are similar to the MORB-like value, might reflect the general character of the upper mantle. The Far Eastern Russian mantle may therefore be a MORB-like source that has been partly infiltrated by subduction-related fluids.

Noble gas studies in CAIs from CV3 chondrites: No evidence for primordial noble gases

Abstract— Calcium‐aluminum‐rich inclusions (CAIs) were among the first solids in the solar system and were, similar to chondrules, created at very high temperatures. While in chondrules, trapped noble gases have recently been detected, the presence of trapped gases in CAIs is unclear but could have important implications for CAI formation and for early solar system evolution in general. To reassess this question, He, Ne, and Ar isotopes were measured in small, carefully separated and, thus, uncontaminated samples of CAIs from the CV3 chondrites Allende, Axtell, and Efremovka.The 20Ne/22Ne ratios of all CAIs studied here are &lt;0.9, indicating the absence of trapped Ne as, e.g., Ne‐HL, Ne‐Q, or solar wind Ne. The 21Ne/22Ne ratios range from 0.86 to 0.72, with fine‐grained, more altered CAIs usually showing lower values than coarse‐grained, less altered CAIs. This is attributed to variable amounts of cosmogenic Ne produced from Na‐rich alteration phases rather than to the presence of Ne‐G or Ne‐R (essentially pure 22Ne) in the samples. Our interpretation is supported by model calculations of the isotopic composition of cosmogenic Ne in minerals common in CAIs. The 36Ar/38Ar ratios are between 0.7 and 4.8, with fine‐grained CAIs within one meteorite showing higher ratios than the coarse‐grained ones. This agrees with higher concentrations of cosmogenic 36Ar produced by neutron capture on 35Cl with subsequent β−‐decay in finer‐grained, more altered, and thus, more Cl‐rich CAIs than in coarser‐grained, less altered ones.Although our data do not strictly contradict the presence of small amounts of Ne‐G, Ne‐R, or trapped Ar in the CAIs, our noble gas signatures are most simply explained by cosmogenic production, mainly from Na‐, Ca‐, and Cl‐rich minerals.

Many-Particle and Many-Hole States in Neutron-Rich Ne Isotopes Related to Broken N = 20 Shell Closure

The low-lying level structures of 26Ne, 28Ne and 30Ne which are related to the breaking of the N=20 shell closure have been studied in the framework of the deformed-basis antisymmetrized molecular dynamics plus generator coordinate method using the Gogny D1S force. The properties of the many-particle and many-hole states are studied as well as that of the ground band. We predict that the negative-parity states, in which neutrons are promoted into the pf-orbit from the sd orbit, have a small excitation energy in the cases of 28Ne and 30Ne. We regard this to be a typical phenomena accompanying the breaking of the N=20 shell closure. It is also found that the neutron 4p4h structure of 30Ne appears at low excitation energy, which contains β+16O correlations.

Properties of nuclei near the neutron-drip line in O – Si region

The analysis of stability and properties of the neutron drip-line isotopes in O – Si region is performed using self-consistent theory of finite Fermi systems (STFFS). The T 1 2 values for new discovered Ne and Na isotopes are calculated. Two-neutron instability of nuclei for extra drip-line nuclei like 26O is discussed. Conclusions about vanishing of N=20 and N=28 as nuclear “magic” numbers and appearance of new drip line numbers N=16 and N=26 are given.

Metastable neon collisions: Anisotropy and scattering length

In this paper we investigate the effective scattering length $a$ of spin-polarized Ne*. Due to its anisotropic electrostatic interaction, its scattering length is determined by five interaction potentials instead of one, even in the spin-polarized case, a unique property among the Bose condensed species and candidates. Because the interaction potentials of Ne* are not known accurately enough to predict the value of the scattering length, we investigate the behavior of $a$ as a function of the five phase integrals corresponding to the five interaction potentials. We find that the scattering length has five resonances instead of only one and cannot be described by a simple gas-kinetic approach or the DIS approximation. However, the probability for finding a positive or large value of the scattering length is not enhanced compared to the single potential case. The complex behavior of $a$ is studied by comparing a quantum mechanical five-channel numerical calculation to simpler two-channel models. We find that the induced dipole-dipole interaction is responsible for coupling between the different |\Omega> states, resulting in an inhomogeneous shift of the resonance positions and widths in the quantum mechanical calculation as compared to the DIS approach. The dependence of the resonance positions and widths on the input potentials turns out to be rather straightforward. The existence of two bosonic isotopes of Ne* enables us to choose the isotope with the most favorable scattering length for efficient evaporative cooling towards the Bose-Einstein Condensation transition, greatly enhancing the feasibility to reach this transition.

The Apollo SWC Experiment: Results, Conclusions, Consequences

The Apollo Solar Wind Composition (SWC) experiment was designed to measure elemental and isotopic abundances of the light noble gases in the solar wind, and to investigate time variations in the solar-wind composition. The experiment was deployed on the first five Apollo lunar landing missions. The crews exposed a foil at each of the five landing sites, and solar wind particles were collected for time periods ranging from 77 minutes in July 1969 (Apollo 11) to 45:05 hours in April 1972 (Apollo 16). The foils were returned to Earth, where the collected noble gas particles were analysed in ultra-high vacuum mass spectrometer systems. We briefly describe here the flight hardware, and the technical tests and calibrations. The experimental results were published in various scientific journals, PhD theses and NASA science reports, some of them not readily accessible after three decades. In this paper, therefore, the results obtained by the five experiments on the fluxes of the isotopes of He, Ne and Ar are summarized and discussed, so that averages and variations in solar wind composition can be more easily compared with more recent data, particularly those to be obtained by the Genesis mission. The helium flux determined for the five exposure periods varied by a factor of four, with a time-weighted average of 1.2 × 107 cm−2 s−1. Although the composition varied much less than the He-flux, definite variations were found for the 4He/3He and He/Ne ratios. The weighted average solar wind abundance ratios obtained were 4He/3He = 2350 ± 120, 4He/20Ne = 570 ± 70, 20Ne/22Ne = 13.7 ± 0.3, 22Ne/21Ne = 30 ± 3, 20Ne/36Ar = 49 ± 7 and 36Ar/38Ar =5.4 ± 0.3 (errors correspond to the 2σ level). We also measured the flow directions of individual isotopic species. We found that the lunar environment did not significantly affect the solar wind composition measured at the lunar surface, and we conclude that the SWC results are representative of the solar wind prevailing in interplanetary space at the time of the five foil exposures. Finally, we discuss, from today's perspective, some of the implications and conclusions that can be drawn from the SWC results, concerning the Sun and its history, the solar system, the galaxy and the universe.

He and Ne isotopes in oceanic crust: implications for noble gas recycling in the mantle

In an attempt to determine the helium and neon isotopic composition of the lower oceanic crust, we report new noble gas measurements on 11 million year old gabbros from Ocean Drilling Program site 735B in the Indian Ocean. The nine whole rock samples analyzed came from 20 to 500 m depth below the seafloor. Helium contents vary from 3.3×10−10 to 2.5×10−7 ccSTP/g by crushing and from 5.4×10−8 to 2.4×10−7 ccSTP/g by melting. 3He/4He ratios vary between 2.2 and 8.6 Ra by crushing and between 2.9 and 8.2 by melting. The highest R/Ra ratios are similar to the mean mid-ocean ridge basalt (MORB) ratio of 8±1. The lower values are attributed to radiogenic helium from in situ α-particle production during uranium and thorium decay. Neon isotopic ratios are similar to atmospheric ratios, reflecting a significant seawater circulation in the upper 500 m of exposed crust at this site. MORB-like neon, with elevated 20Ne/22Ne and 21Ne/22Ne ratios, was found in some high temperature steps of heating experiments, but with very small anomalies compared to air. These first results from the lower oceanic crust indicate that subducted lower oceanic crust has an atmospheric 20Ne/22Ne ratio. Most of this neon must be removed during the subduction process, if the ocean crust is to be recirculated in the upper mantle, otherwise this atmospheric neon will overwhelm the upper mantle neon budget. Similarly, the high (U+Th)/3He ratio of these crustal gabbros will generate very radiogenic 4He/3He ratios on a 100 Ma time scale, so lower oceanic crust cannot be recycled into either MORB or oceanic island basalt without some form of processing.

Ground-State Properties of C, O, and Ne Isotopes in Hartree-Fock-Bogoliubov Calculation with Gogny Interaction**The project supported by the Japanese Society for the Promotion of Science (JSPS) and National Natural Science Foundation of China (NSF) as the bilateral program between Japan and China, National Natural Science Foundation of China under Grant No. 10047001, the China Key Basic Research Development Program under

Ground-state properties of C, O, and Ne isotopes are described in the framework of Hartree–Fock–Bogoliubov theory with density-dependent finite-range Gogny interaction D1S. We include all the contributions to the Hartree–Fock and pairing field arising from Gogny and Coulomb interaction as well as the center of mass correction in the numerical calculations. These ground-state properties of C, O, and Ne isotopes are compared with available experimental results, Hartree–Fock plus BCS, shell model and relativistic Hartree–Bogoliubov calculations. The agreement between experiments and our theoretical results is pretty well. The predicted drip-line is dependent strongly on the model and effective interaction due to their sensitivity to various theoretical details. The calculations predict no evidence for halo structure predicted for C, O, and Ne isotopes in a previous RHB study.

Proton and neutron skins of light nuclei within the relativistic mean field theory

The relativistic mean field (RMF) theory is applied to the analysis of ground-state properties of Ne, Na, Cl and Ar isotopes. In particular, we study the recently established proton skin in Ar isotopes and neutron skin in Na isotopes as a function of the difference between the proton and the neutron separation energy. We use the TMA effective interaction in the RMF Lagrangian, and describe pairing correlation by the density-independent delta-function interaction. We calculate single neutron and proton separation energies, quadrupole deformations, nuclear matter radii and differences between proton radii and neutron radii, and compare these results with the recent experimental data.

Volatile element abundance patterns and an early liquid water ocean on Earth

The abundances of the elements H, C, N, Ne, primordial Ar, Cl, Br, Kr, I and Xe, in the atmo-hydrosphere, continental crust and MORB-source mantle (termed the outer Earth reservoirs (OER)) are examined and compared with solar matter and an average of carbonaceous chondrites (CC). The aim is to assess the likelihood of various possible sources for these volatile elements now on Earth, and discuss and possibly quantify processes whereby volatiles were lost, in order to narrow down scenarios for the earliest terrestrial environment. Al-normalized abundance patterns show a depletion relative to solar matter which varies from 2×10−11 for Ne to 4×10−3 for the halogens. The overall relative pattern is broadly similar to an average abundance pattern of CC, with two to three orders of magnitude depletion relative to this. For H, C, N and the halogens this similarity, against the background of the huge diversity compared to solar matter, makes CC-type material a much more likely source than a gravitationally captured solar atmosphere. A small admixture of solar matter (Alsolar/Altotal≈10−7) acquired in accretion can account for the solar Ne isotope signatures in the deep mantle. The abundance pattern of C, N, Ne, primordial Ar, Br and Kr relative to such a “solar spiked” CC-type source shows depletions dependent of the masses of the molecules (C as CO, N as N2, Br as Br2), which can be modeled assuming a hydrodynamic escape mechanism with H2 fluxes varying from 1 to 3×1013 molecules cm−2 s−1. Relative to this depletion pattern, H (as H2O) and Cl (as HCl) are overabundant by about an order of magnitude. Delivery by comets over Earth history is a highly unlikely explanation for the H overabundance, as measured cometary D/H ratios are ∼2×, and C/H ratios ∼4× higher than those of the OER. The overabundance of both H and Cl can be understood and quantitatively modeled if it is assumed that a liquid water ocean existed in which major portions (on average, between 50 and 70%) of H2O and HCl resided during hydrodynamic escape, so that their volume proportion in the atmosphere (and therefore their loss) was reduced.

Neutron capture cross section measurement of 20,22Ne for stellar nucleosynthesis

We have measured the neutron capture cross sections of 20Ne(n,γ) 21Ne and 22Ne(n,γ) 23Ne at stellar energy by detecting a discrete γ-ray feeding from a neutron capturing state to a low-lying state. In this work the non-resonant direct p-wave capture reaction process has been identified for the first time in the keV neutron capture reactions of Ne isotopes.