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

Background: Recent accumulation of experimental data is revealing nuclear deformation in vicinity of Si-42. This demands 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 mechanism of the nuclear deformations and its relation to the disappearance of the neutron magic number N = 28. 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 Si-42, and suggests that the interband 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 Si-42.

Automated summary

Recent experimental data have shown nuclear deformation in the vicinity of Si-42, prompting systematic theoretical studies to clarify specific aspects of nuclear deformation and its causes. The study investigates the nature and mechanism of nuclear deformations and their relation to the disappearance of the neutron magic number N = 28. Results indicate that shell effects and the loss of magicity lead to various nuclear deformations, with isotones N = 26 and N = 30 having triaxially deformed ground states.