Configuration Mixing Effects Research Articles

Effect of the configuration mixing on the polarization and angular distribution of x-ray line emissions following electron-impact excitation of Ne-like ions.

We present a systematic theoretical study on the angular distribution and linear polarization of x-ray line emissions of neon-like ions following the electron-impact excitation from the ground state to the excited levels [(2p5)1/23d3/2]J=1, [(2p5)3/23d5/2]J=1, [(2p5)3/23d3/2]J=1, and [(2p5)1/23s]J=1. The cross sections are calculated by using the flexible atomic code under configuration-interaction plus many-body perturbation theory method. The angular distribution and linear polarization are obtained based on density matrix theory. Emphasis has been placed on the effect of the configuration mixing on the angular distribution and polarization. It has been proved that the strong mixing of configuration [(2p5)3/23d3/2]J=1 with configuration [(2p5)1/23s]J=1 can result in the abrupt change of Z-dependence of angular distribution and polarization. It indicates that angular distribution and polarization can be expected to serve as a tool for investigation of configuration mixing effect.

Effect of configuration mixing on quadrupole and octupole collective states of transitional nuclei

A model is presented that simultaneously describes shape coexistence and quadrupole and octupole collective excitations within a theoretical framework based on the nuclear density functional theory and the interacting boson model. An optimal interacting-boson Hamiltonian that incorporates the configuration mixing between normal and intruder states, as well as the octupole degrees of freedom, is identified by means of self-consistent mean-field calculations using a universal energy density functional and a pairing interaction, with constraints on the triaxial quadrupole and the axially-symmetric quadrupole and octupole shape degrees of freedom. An illustrative application to the transitional nuclei $^{72}$Ge, $^{74}$Se, $^{74}$Kr, and $^{76}$Kr shows that the inclusion of the intruder states and the configuration mixing significantly lower the energy levels of the excited $0^+$ states, and that the predicted low-lying positive-parity states are characterized by the strong admixture of nearly spherical, weakly deformed oblate, and strongly deformed prolate shapes. The low-lying negative-parity states are shown to be dominated by the deformed intruder configurations.

Apparent change of the 3C/3D line intensity ratio in neonlike ions.

The resonance 3C ([(2p5)1/23d3/2]J=1 → [2p6]J=0) to intercombination 3D ([(2p5)3/23d5/2]J=1 → [2p6]J=0) line intensity ratio of neonlike ions has been studied. The measured line intensity ratio for neonlike Xe44+ ions shows an apparent change, which is reproduced by the calculations using the relativistic configuration interaction plus many-body perturbation theory. It is clearly elucidated that the change in the 3C/3D line intensity ratio is caused by strong configuration mixing between the upper levels of the 3D and 3F ([(2p5)1/23s]J=1 → [2p6]J=0) lines. The present measurement allows us to discuss the 3C/3D line intensity ratio for the highest-Z ions hitherto, which suggests that the experiment-theory discrepancy in the 3C/3D line intensity ratio of neonlike ions diminishes with increasing atomic number Z and further trends to vanish at higher-Z ions. Furthermore, the present study provides benefits to better understand configuration mixing effect in the radiative opacity of hot plasmas.

Classification of resonances and pairing effects on n−A scattering within the Hartree-Fock-Bogoliubov framework

We analyze the properties of the scattering solutions obtained as the pole of the S- and K-matrix with the help of the Jost function framework and the Strum-Liouville theory within the Hartree-Fock-Bogoliubov(HFB) framework, and clarify the scattering solutions which can be defined as the physical state. We found that there are three types of the resonances; "{\it shape resonance}", "{\it particle-type}" and "{\it hole-type quasiparticle resonances}", and another two types of solutions are given as the independent S-matrix and K-matrix poles. The shape resonance is formed by the Hartree-Fock(HF) mean field potential, is not affected by the pairing correlation so much. The particle-type and hole-type quasiparticle resonances originate from the particle and hole states by the configuration mixing effect by pairing. All of resonance are represented by the S-matrix pole which has the corresponding K-matrix pole. Two other types of solutions are given by the independent S-matrix and K-matrix poles. These poles are formed by the HF mean field potential. The effect of pairing for the independent S-matrix pole is small, but the one for the independent K-matrix pole has the remarkable effect. The independent K-matrix pole destroys the quasiparticle resonance as it approaches to the resonance by the pairing effect. The wave function of all resonances have the characteristic structure of the metastable property. However, the metastable structure of the wave function of the quasiparticle resonance can be broken by the independent standing wave solution or the Fano effect.

Nuclear matrix elements of neutrinoless double- β decay in the triaxial projected shell model

The nuclear matrix elements of neutrinoless double-$\beta$ decay for nuclei $^{76}$Ge, $^{82}$Se, $^{100}$Mo, $^{130}$Te, and $^{150}$Nd are studied within the triaxial projected shell model, which incorporates simultaneously the triaxial deformation and quasiparticle configuration mixing. The low-lying spectra and the $B(E2:0^+\rightarrow2^+)$ values are reproduced well. The effects of the quasiparticles configuration mixing, the triaxial deformation, and the closure approximation on the nuclear matrix elements are studied in detail. For nuclei $^{76}$Ge, $^{82}$Se, $^{100}$Mo, $^{130}$Te, and $^{150}$Nd, the nuclear matrix elements are respectively reduced by the quasiparticle configuration mixing by 6%, 7%, 2%, 3%, and 4%, and enhanced by the odd-odd intermediate states by 7%, 4%, 11%, 20%, and 14%. Varying the triaxial deformation $\gamma$ from $0^\circ$ to $60^\circ$ for the mother and daughter nuclei, the nuclear matrix elements change by 41%, 17%, 68%, 14%, and 511% respectively for $^{76}$Ge, $^{82}$Se, $^{100}$Mo, $^{130}$Te, and $^{150}$Nd, which indicates the importance of treating the triaxial deformation consistently in calculating the nuclear matrix elements.

Electron-Impact Excitation of the 5p55d6s2 Autoionizing States in Ba Atom

The excitation cross-sections for the 5p55d6s2 autoionizing states of Ba atoms are studied experimentally and theoretically in an electron-impact energy range from the excitation thresholds of the states up to 600 eV. Experimental data are obtained by determining the intensities of lines in the ejected-electron spectra measured at an observation angle of 54.7∘. The incident-electron and ejected-electron energy resolutions are 0.2 eV and 0.07 eV, respectively. The calculations are performed in the distorted wave approximation by using relativistic radial wave functions obtained in the standard Dirac–Fock–Slater method. For all the states, the experimental cross-sections reach their maxima at low impact energies revealing by that predominantly the spin-exchange character of the excitation of autoionizing states. The structure of the near-threshold maxima indicates the formation of strong negative-ion resonances. At high impact energies, the shape and value of the cross-sections are determined by configuration and state mixing effects.

Coronal Loop Transverse Oscillations Excited by Different Driver Frequencies

Abstract We analyze transverse oscillations of a coronal loop excited by continuous monoperiodic motions of the loop footpoint at different frequencies in the presence of gravity. Using the MPI-AMRVAC code, we perform three-dimensional numerical magnetohydrodynamic simulations, considering the loop as a magnetic flux tube filled in with denser, hotter, and gravitationally stratified plasma. We show the resonant response of the loop to its external excitation and analyze the development of the Kelvin–Helmholtz instability at different heights. We also study the spatial distribution of plasma heating due to transverse oscillations along the loop. The positions of the maximum heating are in total agreement with those for the intensity of the Kelvin–Helmholtz instability, and correspond to the standing wave antinodes in the resonant cases. The initial temperature configuration and plasma mixing effect appear to play a significant role in plasma heating by transverse footpoint motions. In particular, the development of the Kelvin–Helmholtz instability in a hotter loop results in the enhancement of the mean plasma temperature in the domain.

Resonance strengths for KLL dielectronic recombination of highly charged mercury ions and improved empirical Z -scaling law

Theoretical and experimental resonance strengths for KLL dielectronic recombination (DR) into He-, Li-, Be-, and B-like mercury ions are presented, based on state-resolved DR x-ray spectra recorded at the Heidelberg electron beam ion trap. The DR resonance strengths were experimentally extracted by normalizing them to simultaneously recorded radiative recombination signals. The results are compared to state-of-the-art atomic calculations that include relativistic electron-electron correlation and configuration mixing effects. Combining the present data with other existing ones, we derive an improved semi-empirical $Z$-scaling law for DR resonance strength as a function of the atomic number, taking into account higher-order relativistic corrections, which are especially relevant for heavy highly charged ions.

Towers of baryons of the N=2 quark model band in the large Nc limit

We performed a complete analysis of the spectrum of all the states in the ${\cal N}=2$ quark model harmonic oscillator band with $N_f=3$ in the large $N_c$ limit including the often disregarded antisymmetric multiplet $[{\bf 20},1^+]$. We included configuration mixing effects. We found that the states in the $[{\bf 56},L^+]$ and $[{\bf 70},L^+]$ with $L=0,2$ fall into nine towers of degenerate states. We found that nonstrange antisymmetric states fall into three towers and respond to the same structure as the states in the $[{\bf 70},1^-]$ multiplet. We also showed explicitly the compatibility of these results and the scattering resonance picture.

Structure and decays of nuclear three-body systems: The Gamow coupled-channel method in Jacobi coordinates

${\bf Background:}$ Weakly bound and unbound nuclear states appearing around particle thresholds are prototypical open quantum systems. Theories of such states must take into account configuration mixing effects in the presence of strong coupling to the particle continuum space. ${\bf Purpose:}$ To describe structure and decays of three-body systems, we developed a Gamow coupled-channel (GCC) approach in Jacobi coordinates by employing the complex-momentum formalism. We benchmarked the new framework against the complex-energy Gamow Shell Model (GSM). ${\bf Methods:}$ The GCC formalism is expressed in Jacobi coordinates, so that the center-of-mass motion is automatically eliminated. To solve the coupled-channel equations, we use hyperspherical harmonics to describe the angular wave functions while the radial wave functions are expanded in the Berggren ensemble, which includes bound, scattering and Gamow states. ${\bf Results:}$ We show that the GCC method is both accurate and robust. Its results for energies, decay widths, and nucleon-nucleon angular correlations are in good agreement with the GSM results. ${\bf Conclusions:}$ We have demonstrated that a three-body GSM formalism explicitly constructed in cluster-orbital shell model coordinates provides similar results to a GCC framework expressed in Jacobi coordinates, provided that a large configuration space is employed. Our calculations for $A=6$ systems and $^{26}$O show that nucleon-nucleon angular correlations are sensitive to the valence-neutron interaction. The new GCC technique has many attractive features when applied to bound and unbound states of three-body systems: it is precise, efficient, and can be extended by introducing a microscopic model of the core.

Dielectronic recombination of Cu-like W45+

We have investigated dielectronic recombination (DR) for Cu-like W45+ forming Zn-like W44+ by theoretical calculation using the flexible atomic code based on an independent process, isolated resonance, and distorted wave approximation. We have focused on the effect of configuration mixing involving double electron core excitation as well as single electron core excitation on the DR via 3d94l4l′4l″ and 3p53d104l4l′4l″ resonances by inner-shell core excitation Δnc=1. About 20% and over 100% changes in Maxwellian rate coefficient are shown at high energies over 200eV and at low energies near the threshold, respectively, by the configuration mixing. Non-resonant stabilizations (NRS) and decays to autoionizing levels possibly followed by cascades (DAC) to non-closed inner-shells 3d94l4l′4l″ are also considered. The NRS and DAC effect on the DR Maxwellian rate coefficient is relatively smaller than the configuration mixing effect and is less than ~20%. Particular attention has been paid to the DR via 3d104lnl′ resonances by valence-shell core excitation Δnc=0 which was not considered in the previous work (Behar et al., 1997 [4]). The 3d104lnl′ resonances very dominate the DR at low energies below ~100eV. Δnc=2 core excitations are small but not negligible (~10%) relatively at high energy range around 10keV. Our total DR rate coefficient shows the difference with the recombination coefficient on the ADAS database obtained by using a simple semiempirical formula over order of magnitude at low energies and about 30–50% at 2–7keV energy range where W45+ is abundant.

Effects of Configuration and Headspace Mixing on the Accuracy of Closed Chambers for DairyFarm Gas Emission Measurement

<abstract><title><italic>Abstract. </italic></title> This study was aimed at evaluating the influence of chamber configuration (enclosure area and height), the use of a mixing fan and the wind speed induced by the fan at the emitting surface (head space mixing) on the accuracy for the closed chamber in gas emission measurement at low emission rates (≤3000 g SF₆ m^-2 h^-1). A calibration system was designed to generate a reference flux, and SF₆ was used as the target gas. Accuracy or chamber performance was defined based on the agreement between the calculated reference and chamber fluxes, which were not affected by chamber configuration. Four unvented closed chambers with two floor diameters (300 and 400 mm) and three different heights (200, 300, and 400 mm) were tested at seven different emission rates (from 684 ±72 to 2958 ±144 g m^-2 h^-1). Chamber configuration was correlated with the reference flux of sulfur hexafluoride (SF₆), and the tested chambers underestimated the reference fluxes by 21.5% ±13.6% (average ±SD). Chamber enclosure area did not affect the chamber performance while the height significantly impacted measurement accuracy. A chamber height of 300 mm was recommended to measure low gas emission rates. The positive air pressure induced by the mixing fan in the headspace increased with the fan speed, but the chamber performance was not affected by the mixing fan at lower emission rates. For our tested conditions, a mixing fan was not necessary and a vent opening balancing the air pressure inside and outside a chamber was not recommended.

Magnetism of an excited self-conjugate nucleus: precise measurement of the g factor of the 2(1)(+) state in (24)Mg.

A precise measurement of the g factor of the first-excited state in the self-conjugate (N=Z) nucleus (24)Mg is performed by a new time-differential recoil-in-vacuum method based on the hyperfine field of hydrogenlike ions. Theory predicts that the g factors of such states, in which protons and neutrons occupy the same orbits, should depart from 0.5 by a few percent due to configuration mixing and meson-exchange effects. The experimental result, g=0.538±0.013, is in excellent agreement with recent shell-model calculations and shows a departure from 0.5 by almost 3 standard deviations, thus achieving, for the first time, the precision and accuracy needed to test theory. Proof of the new method opens the way for wide applications including measurements of the magnetism of excited states of exotic nuclei produced as radioactive beams.

Effects of configuration mixing in heavy-ion elastic scattering

A theoretical study of the influence of configuration mixing on elastic scattering cross section is performed for the system 16O + 27Al at 100 MeV. A simple twostate model space, including the 27Al 5/2+ ground and 5/2+ excited state at 2.73 MeV, is used in the coupled channel equations. The results indicate that even a weak degree of mixing is able to sizeably affect the elastic cross section, determining mainly a damping of Fraunhofer oscillations, as observed in the experiments.

K-p → Σ0π0, Λπ0, $\bar{K}^0n$, ηΛ reactions in a quark model

In this talk, we report our main results on the study of the low-energy reactions K-p → Σ0π0, Λπ0, [Formula: see text], ηΛ in a quark model. This model might be a powerful approach to deal with these low-energy reactions. In the analysis, we find that the u- and t-channel backgrounds play crucial roles in the low-energy [Formula: see text] scatterings. Significant evidence of some low-lying Λ and Σ hyperon resonances in these processes are found. Furthermore, we obtain some properties of the low-lying Λ and Σ hyperon resonances. For example, Λ(1670)S01 should have a much stronger coupling to ηΛ, while having a weaker coupling to [Formula: see text] than that derived in the SU(6) ⊗ O(3) limit; the coupling of Λ(1690)D03 to ηΛ is very small. The configuration mixing effects might be crucial to understand the strong interaction properties of the low-lying negative Λ resonances.

Higher-order resonant electronic recombination as a manifestation of configuration interaction

Theoretical and experimental investigations of higher-order electron–ion recombination resonances including inter-shell excitations are presented for L-shell ions of Kr with the aim of examining details of atomic structure calculations. The particular importance of electron–electron interaction and configuration mixing effects for these recombination processes enables their use for detailed tests of electron correlation effects. A test of the required level of considered mixing configurations is presented and further experiments involving higher-order recombination channels are motivated.

Lifetime and Fragment Correlations for the Two-Neutron Decay ofO26Ground State

The structure and decay of 26O are investigated in a three-body 24O+n+n model suitable for studies of the long-lived (including radioactivity time scale) states. We have found extremely strong effects of the subbarrier configuration mixing on the decay width of true 2n emitters due to core recoil and neutron-neutron final state interaction. This effect far exceeds the analogous effect in the true 2p emitters. Our calculations provide reasonably narrow boundaries for the lifetime vs decay energy dependence for the true 2n emission. An upper limit of ∼1 keV for the decay energy of the unbound 26O is inferred based on the recent experimental lifetime value.

Configuration mixing effects in neutron-rich carbon isotopes

Shell model calculations are done to study the structure of neutron-rich carbon isotopes. For both even-A and odd-A neutron-rich carbon isotopes, the energy levels are strongly affected by the configuration mixing of valence neutrons. The calculated energy levels in the nucleus 17C are significantly improved compared with experimental values when the model space of the three valence neutrons is enlarged from pure v(0d5/2)3 configuration to full sd space. We also investigate the configuration mixing effect on the B(E2) values in even-even nuclei 16-20C.

Neutrinoless ββ decay nuclear matrix elements in an isotopic chain

We analyze nuclear matrix elements (NME) of neutrinoless double beta decay calculated for the cadmium isotopes. Energy density functional methods including beyond mean field effects such as symmetry restoration and shape mixing are used. Strong shell effects are found associated to the underlying nuclear structure of the initial and final nuclei. Furthermore, we show that NME for two-neutrino double beta decay evaluated in the closure approximation, Mcl2ν, display a constant proportionality with respect to the Gamow–Teller part of the neutrinoless NME, MGT0ν. This opens the possibility of determining the MGT0ν matrix elements from β∓ Gamow–Teller strength functions. Finally, the interconnected role of deformation, pairing, configuration mixing and shell effects in the NMEs is discussed.

Complete sets of polarization transfer observables for the208Pb(p⃗,n⃗)reaction at 296 MeV and Gamow-Teller and spin-dipole strengths for208Pb

We report measurements of cross sections and analyzing powers for reaction angles of ${\ensuremath{\theta}}_{\mathrm{lab}}={0.0}^{\ensuremath{\circ}}$--${10.0}^{\ensuremath{\circ}}$ and complete sets of polarization transfer observables and induced polarizations at ${\ensuremath{\theta}}_{\mathrm{lab}}={0.0}^{\ensuremath{\circ}}$--${7.0}^{\ensuremath{\circ}}$ for the ${}^{208}\mathrm{Pb}(\stackrel{P\vec}{p},\stackrel{P\vec}{n})$ reaction at a bombarding energy of ${T}_{p}=296$ MeV. A multipole decomposition technique was applied to the data to extract the Gamow-Teller (GT) and spin-dipole (SD) components from the continuum. The polarization observables were also used, for the first time, to separate the SD components into different spin-parity transfer ($\ensuremath{\Delta}{J}^{\ensuremath{\pi}}={0}^{\ensuremath{-}}$, ${1}^{\ensuremath{-}}$, and ${2}^{\ensuremath{-}}$) contributions. A significant strength with $\ensuremath{\Delta}{J}^{\ensuremath{\pi}}={1}^{+}$ is identified in the continuum beyond the GT giant resonance, which is due to configuration mixing effects and the isovector spin monopole (IVSM) contribution. The SD strength distributions were clearly dependent on $\ensuremath{\Delta}{J}^{\ensuremath{\pi}}$, which is reasonably reproduced by Hartree-Fock (HF) plus random phase approximation (RPA) calculations that include the Skyrme interaction with tensor components [Phys. Rev. C 83, 054316 (2011)].