Year: 2024
Type: article
Abstract: The halo phenomenon has long been a frontier in experimental and theoretical nuclear physics research. Over nearly forty years of exploration, signals of halos have been identified in approximately 20 nuclei, with 37Mg being the heaviest among them. The worldwide development of rare isotope beam facilities continues to advance the experimental exploration of new halo nuclei in the A≈40 mass region. Meanwhile, relevant theoretical predictions are increasingly desirable. The relativistic density functional theory is a crucial tool for studying halo nuclei. The deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) is capable of describing deformed exotic nuclei by incorporating self-consistently axial deformation degrees of freedom, pairing correlations, and continuum effects. It has provided microscopic descriptions for several known halo nuclei, such as 31Ne and 37Mg. The success of the DRHBc theory is further evidenced by the high-precision DRHBc mass table and related applications to various nuclear phenomena. The DRHBc theory has predicted the newly discovered nuclide 39Na and the yet-to-be-synthesized 42Mg as deformed halo nuclei. It has been found that the lowering of the 2p orbitals in the spherical limit causes the collapse of the N=28 shell closure in 39Na, leading to a well-deformed ground state. Pairing correlations, together with the mixing of pf components driven by deformation, result in the occupation of weakly bound or continuum p-wave neutron orbitals. Consequently, an oblate halo forms around the prolate core in 39Na. The experimental neutron separation energies and empirical matter radii of neutron-rich magnesium isotopes, along with the deformed p-wave halo characteristics of 37Mg, are well reproduced by the DRHBc theory. A deformed neutron halo in 42Mg is revealed through the analysis of angle-averaged densities as well as densities along and perpendicular to the symmetry axis for magnesium isotopes. It is shown that the deformation of a potential neutron halo depends essentially on the quantum numbers of the main components of the halo orbital(s). The triaxial relativistic Hartree-Bogoliubov theory in continuum (TRHBc), which considers triaxiality, pairing correlations, and continuum effects, has been recently developed to explore triaxial halo nuclei. The TRHBc calculated neutron separation energies and charge radii for aluminum isotopes show good agreement with available experimental data. The heaviest observed odd-odd aluminum isotope, 42Al, is predicted to be a triaxial halo nucleus with a novel shape decoupling, characterized by an exchange of intermediate and short axes from the well-deformed core to the super-deformed halo. Combining nuclear reaction models with the DRHBc or TRHBc theory to provide a unified description of known halo nuclei and predict new ones, from structural properties to reaction dynamics, is a topic worthy of long-term exploration. Further applications of the DRHBc and TRHBc theories to other exotic phenomena near the dripline are also anticipated in the future.
DOI: 10.1360/tb-2024-0918
Authors: Kaiyuan Zhang, Cong Pan, Lulu Li, Xiang-Xiang Sun, Shi-Sheng Zhang
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W4403905593