2024
- Kenichi Yoshida (RCNP, Osaka University), “Triaxial-shape dynamics in the low-lying excited 0^+ state: Roles of the collective mass“, 31 January 2024
Abstract: Non-yrast states in neutron-rich nuclei are being investigated experimentally. These states reveal various aspects and details of the nuclear structure, such as the fluctuation around the axially symmetric shape. We have investigated the beyond-mean-field effects in low-energy states of neutron-rich nuclei around N=28. We focused on the role of collective mass in triaxial-shape dynamics. To this end, we employed the five-dimensional quadrupole collective Hamiltonian method with the potential obtained in a constrained Hartree-Fock-Bogoliubov approach with a Skyrme energy-density functional and the collective-mass functions obtained by the cranking approximation. The method includes triaxial deformations. We found that 42Mg, 40Si, 44S, and 46S show γ-soft: A flat behavior in the potential energy surface along the triaxial deformation. Their low-lying spectra show a strong nucleus dependence, while those obtained with a collective mass assumed as constant are similar to each other. The energy ratio E(0^+_2)/E(2^+_1) and the B(E2) ratio B(E2;0^+_2→2^+_1)/B(E2;2^+_1→0^+_1) show a unique property of the 0^+_2 state.
- Daisuke Suzuki (RIKEN), “Mirror Symmetry of Atomic Nuclei“, 17 January 2024
Abstract: Symmetry and its breaking are fundamental in physical phenomena. Atomic nuclei are no exception. The mirror symmetry is one of the symmetries governing the structure of atomic nuclei. It dictates the structure of nuclei with an excess of protons to be identical to the structure of the so-called mirror nuclei with the same excess of neutrons. Originated in the symmetry of the nuclear force between proton-proton and neutron-neutron, the mirror symmetry is known to rather rigorously be expressed, for instance, in level energies of mirror nuclei. It is however revealed in recent studies that radioactive isotopes (RI) at far edges of stability do not always abide by the mirror symmetry. Various symmetry breaking mechanisms are understood from structural evolutions of atomic nuclei toward the limit of existence. In this talk, I will give an overview of the mirror symmetry of atomic nuclei and recent understanding from spectroscopy of proton-rich nuclei by using RI beams.
2023
- Masaaki Kimura (RIKEN), “Visualizing the Shape of Nuclei“, 15 December 2023
Abstract: Nuclei have rotational symmetry as isolated systems; however, the internal structures of many nuclei break this symmetry, resulting in various shapes (spontaneous symmetry breaking). The shape of a nucleus is related to the arrangement of protons and neutrons within the nucleus, the structure of the Fermi surface, and affects fundamental quantities of the nucleus such as mass, electrical, and magnetic properties. Consequently, extensive research has been devoted to understanding nuclear shapes. Directly measuring the shape of nuclei is challenging, and discussions often rely on indirect physical quantities like electric moments. Thus, we propose a method using experimental data of electric transition density to reconstruct the shape of nuclei based on minimal theoretical processes. In the seminar, we will discuss the reconstructed shape of a carbon-12 nucleus derived from the real experimental data.
- Tokio Fukahori (Japan Atomic Energy Agency), “核データライブラリーの切り開く可能性” (in Japanese), 28 July 2023.
Abstract: 核データは原子力エネルギー分野をはじめとし、多くの非エネルギー分野の工学、医学、基礎物理の基本データとして重要なデータである。近年、日本原子力研究開発機構では、わが国を代表する評価済み核データであるJENDLの第5版（JENDL-5）を公開した。本セミナーでは、まず、基礎物理定数としての核データ、核データの利用分野、核データの整備の方法、核データ整備に係る国際協力等の基礎的な知見を紹介する。これとともに、核データの将来のあり方として、未来形に関して議論したい。また、この議論に基づき今後の核データの発展のための方策を検討する。
- Luka Lotina (University of Zagreb), “The sdg interacting boson model from the relativistic energy density functional“, 24 July 2023.
Abstract: In this seminar, a work is presented on the relativistic energy density functional (REDF) – based sdg interacting boson model (IBM). By mapping the potential energy surface (PES) obtained through self-consistent mean-field (SCMF) calculations with the relativistic DD-PC1 functional, and with constraints placed on the axial quadrupole and hexadecapole deformation parameters, the parameters of the sdg IBM Hamiltonian were determined for isotopes 148-160Gd . The sdg IBM Hamiltonian was used to calculate low-lying excitation energies and transition strengths. The results were compared to the results obtained with the sd IBM calculations and with the experimental data. The excitation energies are in good agreement with the experimental data. The mapped sdg IBM significantly improves the calculated energies of higher states in the ground state band compared to the sd IBM. The calculated E2, E4 and E0 transitions are mostly in good agreement with the available data, however, they show no significant improvement over the results obtained with the sd IBM.