Systematic investigation of low-lying dipole modes using the canonical-basis time-dependent Hartree-Fock-Bogoliubov theory

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Background:The five-dimensional quadrupole collective model based on energy density functionals (EDFs) has often been employed to treat long-range correlations associated with shape fluctuations in nuclei. Our goal is to derive the collective inertial functions in the collective Hamiltonian by the local quasiparticle random-phase approximation (QRPA) that correctly takes into account time-odd mean-field effects. Currently, a practical framework to perform the QRPA calculation with the modern EDFs on the (β,γ ) deformation space is not available. Purpose: Toward this goal, we develop an efficient numerical method to perform the QRPA calculation on the (β,γ ) deformation space based on the Skyrme EDF. Methods: We use the finite amplitude method (FAM) for the efficient calculation of QRPA strength functions for multipole external fields. We construct a computational code of FAM-QRPA in the three-dimensional Cartesian coordinate space to handle triaxially deformed superfluid nuclei. Introduction. The shape of atomic nuclei is influenced strongly by the quantum nature of nuclear systems. Excitation spectra and their transition probabilities clearly indicate the existence of shape fluctuations and shape coexistence [1], particularly in transitional regions from spherical to deformed shapes in the ground state. The long-lived fission products (LLFP) from uranium fueled reactors, such as Pd and Zr isotopes, are located in transitional regions on the nuclear chart and demonstrate the shape mixing and coexistence. It is important to understand the basic properties of the LLFPs to develop a possible nuclear transmutation method, which is the main target of an ImPACT program "Reduction and Resource Recycling of High-level Radioactive Wastes through Nuclear Transmutation" [2].One of the standard methods of investigating nuclear manybody problems is the nuclear energy density functional (EDF) theory [3]. The nuclear EDF well describes the ground-state properties of atomic nuclei. However, on the mean-field level, it cannot describe shape fluctuations and shape coexistence. We need to go beyond the mean field for a description of such phenomena, including quantum fluctuations associated with the large-amplitude collective motion. If the EDF were constructed as an expectation value of a well-defined Hamiltonian, a possible extension would be the generator coordinate method (GCM) [4][5][6]. However, most of the EDFs are known to have a singular behavior [7,8], which prevents us from the straightforward application of the GCM.

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confidence: 99%

“…A typical mass region of appearance of the triaxial ground state is the A ≈ 100 region and Pt isotopes [31,32]. Here we take 110 Ru and 190 Pt, calculated with the SkM * EDF.…”

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confidence: 99%

Multipole modes of excitation in triaxially deformed superfluid nuclei

Washiyama

Nakatsukasa

2017

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“…where the cutoff function f (ε) depends on the single-particle energy ε τ 0 l in the ground state [33,34]. In this work, we tested several choices of the pairing strength G τ 0 , which will be explained in the next section.…”

Section: B Choice Of Energy Density Functionalmentioning

confidence: 99%

“…To access the low-lying quadrupole modes of these isotopes, we apply the canonical-basis time-dependent Hartree-FockBogoliubov (Cb-TDHFB) theory [33] which has been successfully applied to the study of the dipole [33,34] and quadrupole [35] resonances of nuclei of wide mass range. The Cb-TDHFB can describe self-consistently the dynamical effects of pairing correlation which has a significant role in generating the low-lying quadrupole strength, as reported in Refs.…”

Section: Introductionmentioning

confidence: 99%

Low-lying2+states generated bypn-quadrupole correlation andN=28shell quenching

Ebata

Kimura

2015

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The quadrupole vibrational modes of neutron-rich N = 28 isotones ( 48 Ca, 46 Ar, 44 S, and 42 Si) are investigated by using the canonical-basis time-dependent Hartree-Fock-Bogoliubov theory with several choice of energy density functionals, including nuclear pairing correlation. It is found that the quenching of the N = 28 shell gap and the proton holes in the sd shell trigger quadrupole correlation and increase the collectivity of the low-lying 2 + state in 46 Ar. It is also found that the pairing correlation plays an important role to increase the collectivity. We also demonstrate that the same mechanism to enhance the low-lying collectivity applies to other N = 28 isotones 44 S and 42 Si, and it generates a couple of low-lying 2 + states which can be associated with the observed 2 + states.

“…The experiment performed at RIKEN reported the PDR of 26 Ne around E x = 9 MeV with the integrated E1 strength of B(E1) = 0.49 ± 0.16 e 2 fm 2 which exhausts approximately 5% of the Thomas-ReicheKuhn (TRK) sum rule [14]. Many theoretical studies based on the quasiparticle random phase approximation (QRPA) have been performed and have successfully described these observed properties, although the results range between E x = 6-10 MeV and 5%-10% of the TRK sum rule depending on the effective interactions used in the calculations [10,[15][16][17][18][19][20][21][22][23].…”

Section: Introductionmentioning

confidence: 99%

Structure and decay of the pygmy dipole resonance in Ne26

Kimura

2017

The low-lying spectra of 24,25,26 Ne and the structure of the pygmy dipole resonance (PDR) in 26 Ne have been theoretically studied by the antisymmetrized molecular dynamics (AMD) and its extended version called shifted-basis AMD. The calculated energy and strength of the PDR reasonably agree with the observation, and the analysis of the wave function shows that the PDR is dominated by neutron excitation coupled to the quadrupole excited core nucleus 25 Ne, which explains the observed unexpected decay of PDR to the excited states of 25 Ne. The large isoscalar component of PDR is also shown and the enhancement of the core excitation in neutron-rich Ne isotopes is conjectured.