Triaxial deformation and the loss of the N = 28 shell gap

Abstract

Background: Recent accumulation of experimental data is revealing the nuclear deformation in vicinity of 42Si. This requests systematic theoretical studies to clarify more specific aspects of nuclear deformation and its causes. Purpose: The purpose of this study is to investigate the nature and cause of the nuclear deformations and its relation to the loss of the neutron magic number N = 28 in vicinity of 42Si. Method: The framework of antisymmetrized molecular dynamics with Gogny D1S density functional has been applied. The model assumes no spatial symmetry and can describe triaxial deformation. It also incorporates with the configuration mixing by the generator coordinate method. Results: We show that the shell effects and the loss of the magicity induce various nuclear deformations. In particular, the N = 26 and N = 30 isotones have triaxially deformed ground states. We also note that the erosion of the N = 28 magicity gradually occurs and has no definite boundaries. Conclusion: The present calculation predicts various nuclear deformations in vicinity of 42Si and suggests that the inter-band electric transitions are good measure for it. We also remark that the magicity is lost without the single-particle level inversion in the oblate deformed nuclei such as 42Si.

arXiv comment18 pages, 4 figures

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• $SO(3)$ quadratures in angular-momentum projection
• Triaxial-shape dynamics in the low-lying excited $0^{+}$ state: Role of the collective mass
• Cranked Skyrme-Hartree-Fock-Bogoliubov approach for a mean-field description of nuclear rotations near the drip line
• Five-dimensional collective Hamiltonian with improved inertial functions
• Evolution of giant monopole resonance with triaxial deformation
• Determination of proton and neutron contributions to the $0_{g.s.}^{+}\to 2_1^{+}$ excitations in ${}^{42}$Si and ${}^{44}$S using inelastic proton scattering in inverse kinematics and intermediate energy Coulomb excitation