Single-particle Configurations Research Articles

Studies of light neutron-excess systems from bound states to continuum

The generalized two-centre cluster model (GTCM), which can handle various single-particle configurations in general two-centre systems, is applied to the light neutron-rich system, 12Be = α+α+4N. We discuss the change of the neutrons' configuration around two α cores as the excitation energy varies. We show that the excess neutrons form various chemical-bonding-like configurations around the two α cores in the unbound region above the α-decay threshold. The possibility of α-cluster formation in a heavier system with neutron excess, 28Ne, is also discussed.

Theoretical study of rotational and multi-phonon γ-vibrational structure in neutron-rich Zr, Mo, and Ru nuclei

A theoretical study for some neutron-rich nuclei in the A = 100-110 mass region is carried out by using the angular-momentum-projection technique implemented in the projected shell model. By assuming an axial symmetry in the deformed basis, the influence of the high-j h11/2 neutron orbital and the g9/2 proton orbital on the structure of strongly-deformed, neutron-rich even-even and odd-mass Zr isotopes is investigated. For even-even isotopes, the structure of multi-quasiparticle bands in 102Zr is taken as an example and properties along the yrast line are analyzed in detail. For odd-neutron isotopes, the discussion is focused on the excited single-particle configurations. We also perform calculations by employing a triaxially-deformed basis to study multi-phonon γ vibrational bands in 110Mo and to interpret the anharmonicity observed in the one- and two-phonon γ vibrational bands in 114Ru.

Studies of Light Neutron-Excess Systems from Bounds to Continuum

The generalized two-center cluster model, which can handle various single particle configurations in general two center systems, is applied to the light neutron-rich system, 12Be = α+α+4N. We discuss the change of the neutrons’ configuration around two α-cores as a variation of an excitation energy. We show that the excess neutrons form various chemical-bonding-like configurations around two α cores in the unbound region above the α decay threshold. The possibility of the α cluster formation in the heavier neutron-excess system, 28Ne, is also discussed.

Existence of an Exotic Torus Configuration in High-Spin Excited States ofCa40

We investigate the possibility of the existence of the exotic torus configuration in the high-spin excited states of (40)Ca. We here consider the spin alignments about the symmetry axis. To this end, we use a three-dimensional cranked Skyrme Hartree-Fock method and search for stable single-particle configurations. We find one stable state with the torus configuration at the total angular momentum J=60 ħ and an excitation energy of about 170 MeV in all calculations using various Skyrme interactions. The total angular momentum J=60 ħ consists of aligned 12 nucleons with the orbital angular momenta Λ=+4, +5, and +6 for spin-up or -down neutrons and protons. The obtained results strongly suggest that a macroscopic amount of circulating current breaking the time-reversal symmetry emerges in the high-spin excited state of (40)Ca.

New approaches to assign configurations using low-statistic γ-ray spectra

Analytical methods to deduce single particle configurations from g K factors using branching ratios in rotational bands, especially in low-statistic cases for heavy nuclei, will be presented. Two methods utilising γ-ray branching ratios in rotational bands and also intensities in the K X-ray region of spectra are shown and results from these are given.

Studies of light neutron-excess nuclei from bound to continuum

The generalized two-center cluster model (GTCM), which can handle various single particle configurations in general two center systems, is applied to the light neutron-rich system, 12Be = α + α + 4N. We discuss the change of the neutrons' configuration around two a-cores as a variation of an excitation energy. The covalent, ionic and atomic configurations coexists with the degenerate feature above the α+8Heg.s. particle-decay threshold. We find the strong enhancement in the monopole excitation from the ground state to the excited states. The GTCM calculation is also applied to even Be isotopes, and the systematics on the structural changes from bound region to continuum is discussed.

Symmetry-Adapted Ab Initio Open Core Shell Model Theory

By using only a fraction of the model space, we gain further insight – within a symmetry-guided no-core shell model framework – into the many-body nuclear dynamics that gives rise to important single-particle configurations together with correlated highly-deformed and alpha-cluster structures. We show results of the novel ab initio symmetry-adapted no-core shell model for large-scale nuclear structure computations. In addition, we use the symmetry patterns unveiled in these results to explore ultra-large model spaces.

Geometrical impact on the optical polarization of droplet epitaxial quantum dots

We report on experimental and theoretical investigations of the optical anisotropy of GaAs/AlGaAs quantum dots grown by droplet epitaxy. With in situ annealing in the growth, the shape of quantum dots is systematically controlled from a tall and laterally symmetric shape to a flat and laterally elongated one. Photoluminescence spectroscopy demonstrates an uncommon observation: the more elongated the quantum dots, the lower the degree of linear polarization. Theoretical analysis based on a four-band $\mathbf{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{p}$ theory reveals a substantial impact of vertical confinement on the valence heavy-hole and light-hole mixing, which leads to the enhancement of polarization anisotropy for taller quantum dots. The influence of Coulomb interactions on polarization anisotropy is studied by using the partial configuration interaction method, and is shown to reduce the polarization anisotropy through the mixing of single-particle configurations with different symmetries.

Integrated autothermal oxidative coupling and steam reforming of methane. Part 2: Development of a packed bed membrane reactor with a dual function catalyst

A numerical feasibility study was performed on the integral performance of dual function catalyst particles in a packed bed reactor equipped with a porous membrane for distributive feeding of oxygen. The exothermic oxidative coupling and the endothermic steam reforming of methane (for simultaneous production of ethylene and synthesis gas) are integrated at the level of a porous catalyst particle with distributed activity, where the presence of the intraparticle heat-sink strongly reduces the total reaction heat and the temperature gradients in the reactor, eliminating the need for expensive conventional cooling of the reactor.Numerical simulations, with reaction kinetics taken from the literature, revealed that with distributive oxygen feeding via membranes indeed the local oxygen concentration in the packed bed membrane reactor can be kept low, which combined with a high Thiele modulus for oxidative coupling makes dual function catalysis possible. Using a reforming core diameter of approximately 15–40μm, the steam reforming and oxidative coupling reaction rates could be effectively tuned to achieve autothermal operation, while the methane conversion was enhanced from 34 to 48% at optimum C2 production rates. In addition, it was shown that the temperature profiles in the reactor can be strongly reduced by employing the dual function catalyst and that the use of axial oxygen membrane flux profiles enables the use of a single particle configuration to approach autothermal operation in the entire reactor.

Shape Co-Existence in the Transitional Nuclide 157Yb

High-spin states in 157Yb have been populated in the 144Sm(16O, 3n)157Yb fusion-evaporation reaction at a beam energy of 85 MeV, and two rotational bands have been established for the first time. Within the framework of the triaxial particle-rotor model, the energy spectra and single-particle configurations of 157Yb are investigated. The calculated energy spectra agree well with the experimental data. The newly observed νf7/2 band, and the previously known νi13/2 band in 157Yb, are also discussed by means of Total-Routhian-Surface methods. The structural characters observed in 157Yb provide evidence for the shape coexistence of three distinct shapes: prolate, triaxial and oblate. At higher spins, both the νf7/2 band and the νi13/2 band in 157Yb undergo a shape evolution with sizable alignments occurring.

Studies of Light Neutron-Excess Nuclei from Bounds to Continuum

The generalized two-center cluster model, which can handle various single particle configurations in general two center systems, is applied to the light neutron-rich system, 12Be = α+α+4N. We discuss the change of the neutrons’ configuration around two α-cores as a variation of an excitation energy. We show that the excess neutrons form various chemical-bonding-like configurations around two α cores in the unbound region above the α decay threshold. The possibility of the α cluster formation in the heavier neutron-excess system, 28Ne, is also discussed.

Studies of Light Neutron-Excess Nuclei from Bounds to Continuum

The generalized two-center cluster model (GTCM), which can handle various single particle configurations in general two center systems, is applied to the light neutron-rich system, 12Be = α + α + 4N. We discuss the change of the neutrons' configuration around two α-cores as a variation of an excitation energy. The covalent, ionic and atomic configurations coexist with the degenerate feature above the α+8Heg.s. particle-decay threshold. We find the strong enhancement in the monopole excitation from the ground state to the excited states. The GTCM calculation is also applied to even Be isotopes, and the systematics on the structural changes from bound region to continuum is discussed.

Medium- and high-spin band structure of the chiral-candidate nucleus134Pr

Medium- and high-spin states of ${}^{134}$Pr were populated using the ${}^{116}$Cd(${}^{23}\text{Na},5n$) reaction and studied with the GAMMASPHERE spectrometer. Several new bands have been found in this nucleus, one of them being linked to the previously observed chiral-candidate twin-band structure. The ground state of ${}^{134}$Pr could be determined through establishing a level structure that connects the two previously known long-lived isomeric states. Unambiguous spin-parity assignments for the excited states could be performed based on the known 2${}^{\ensuremath{-}}$ spin-parity of the ground state combined with the present experimental data. Intrinsic single-particle configurations have been assigned to the newly observed bands on the basis of the measured $B(M1)/B(E2)$ ratios, alignments, band-crossing frequencies, bandhead spins, the observed single-particle configurations in the neighboring nuclei, and taking into account the predictions of total Routhian surface and tilted-axis cranking calculations.

Publisher’s Note: Emergence of theN=16shell gap in21O [Phys. Rev. C84, 011301(R) (2011)

The spectroscopy of 21O has been investigated using a radioactive 20O beam and the (d,p) reaction in inverse kinematics. The ground and first excited states have been determined to be Jpi=5/2+ and Jpi=1/2+ respectively. Two neutron unbound states were observed at excitation energies of 4.76 +- 0.10 and 6.16 +- 0.11. The spectroscopic factor deduced for the lower of these interpreted as a 3/2+ level, reveals a rather pure 0d3/2 single-particle configuration. The large energy difference between the 3/2+ and 1/2+ states is indicative of the emergence of the N=16 magic number. For the higher lying resonance, which has a character consistent with a spin-parity assignment of 3/2+ or 7/2-, a 71% branching ratio to the first 2+ state in 20O has been observed. The results are compared with new shell model calculations.

ASYMMETRIC CLUSTERS IN 14Be

The generalized two-center cluster model (GTCM), which can treat various single particle configurations in general two-center systems, is applied to 14 Be =α+α+6N. We mainly investigate an appearance of asymmetric cluster structures, 6 He +8 He , in the excited states of 14 Be . The level scheme in 14 Be is discussed in a comparison with that in 10 Be . The relation between 14 Be and 10 Be can be understood from the viewpoint of the particle-hole symmetry in the x He +y He cluster configuration.

Studies of light neutron-excess systems from bounds to continuum

The generalized two-center cluster model (GTCM), which can handle various single particle config urations in general two center systems, is applied to the light neutron-rich system, 12 Be= α+α+4N . We discuss the change of the neutrons’ configuratio around two α-cores as a variation of an excitation energy. We show that the covalent, ionic and atomic configuration appear in the unbound region above the α+8 Heg.s. particledecay threshold. The GTCM calculation is also applied to even Be isotopes, and the systematics on the structural changes from bound region to continuum is discussed.

Assignment of single particle configurations in odd-A nuclei near A~100 with angular correlation measurements

The multipole mixing ratios of ΔI = 1 transitions between levels in rotational bands built on single-particle states in odd neutron nuclei are dependent on the configurations of the states. In particular, the mixing ratio can be used to distinguish between several possible single-particle configurations if interpreted with the particle plus axial-rotor model (PRM). This work features the first determination of the ground-state configurations of 109,111Ru. The single-particle structures of the ground states of 101Zr and 103,105,107Mo as well as excited states in 103,107Mo are also investigated, with a new result found in 107Mo.

ASYMMETRIC CLUSTERS IN EVEN Be ISOTOPES

The generalized two-center cluster model (GTCM), which can treat various single particle configurations in general two center systems, is applied to light neutron-rich systems, Be isotopes (α+α+ X N). We discuss the change of the neutrons' configuration around two α-cores as a variation of an excitation energy. We show that the asymmetric clusters, which correspond to the atomic or ionic configurations, appear in the unbound region above the α particle-decay threshold systematically.

Internal electronic structure and fine structure of multiexcitons in semiconductor quantum dots

We perform a detailed theoretical study of the characteristic internal electronic structure of various multiexcitons $({N}_{h},{N}_{e})$, where ${N}_{h}$ is number of holes and ${N}_{e}$ is the number of electrons in the self-assembled semiconductor quantum dots (QDs). For each of the leading $({N}_{h},{N}_{e})$ excitonic complexes we start from the single-particle configuration (e.g., a specific occupation pattern of $S$ and $P$ electron and hole levels by a few carriers) and then show the many-particle multiplet levels for the initial state of emission $({N}_{h},{N}_{e})$ and the final state of emission $({N}_{h}\ensuremath{-}1,\text{ }{N}_{e}\ensuremath{-}1)$. We denote which states are dark and which are bright; the order and multiplicity, the leading single-particle character of each multiplet state, and the fine-structure splittings. These are of general utility. We also show explicit numerical values for distances between various transitions for four specific QDs. Here the presented information is important and potentially useful for a few reasons: (i) the information serves as a guide for spectroscopic interpretation; (ii) the information reveals non-Aufbau cases, where the dot does not have Aufbau occupation of carriers' levels; (iii) the information shows which transitions are sensitive to random-alloy fluctuations (if the dot is alloyed) and importance of this effect. We show that because of such alloy information, distances between peaks cannot be used to gauge structural information.

Single particle states in neutron-richZr101,Mo103,105,107, andRu109,111

The multipole mixing ratios of $\ensuremath{\Delta}I=1$ transitions between levels in rotational bands built on single-particle states in odd neutron nuclei are dependent on the configurations of the states. In particular, the mixing ratio can be used to distinguish between several possible single-particle configurations if interpreted with the particle-axial-rotor model. This work features the first determination of the ground-state configurations of $^{109,111}\mathrm{Ru}$. The single-particle structures of the ground states of $^{101}\mathrm{Zr}$ and $^{103,105,107}\mathrm{Mo}$ as well as excited states in $^{103,107}\mathrm{Mo}$ are also investigated, with a new result found in $^{107}\mathrm{Mo}$.