Shrunk halo and quenched shell gap at N = 16 in 22C: Inversion of sd states and deformation effects

Xiang-Xiang Sun,Jie Zhao,Shan-Gui Zhou

doi:10.1016/j.physletb.2018.08.071

Abstract

We explore the interplays among the formation of a halo, deformation effects, the inversion of sd states, the shell evolution, and changes of nuclear magicities in 22C by using a deformed relativistic Hartree–Bogoliubov model in continuum. It is revealed that there is an inversion between the two spherical orbitals 2s1/2 and 1d5/2 in 22C compared with the conventional single particle shell structure in stable nuclei. This inversion, together with deformation effects, results in a shrunk halo and a quenched shell gap at N=16. It is predicted that the core of 22C is oblate but the halo is prolate. Therefore several exotic nuclear phenomena, including the halo, the shape decoupling effects, the inversion of sd states, and the evolution of shell structure which results in (dis)appearance of magic numbers, coexist in one single nucleus C22.

Highlights

The study of exotic nuclear structure is at the forefront of research in modern nuclear physics [1]
The formation of a nuclear halo is closely connected with the evolution of the shell structure and changes of nuclear magicities around drip-lines [13, 14, 15, 16]
It is clearly seen that the neutrons extend spatially much farther than the protons, hinting a neutron halo in 22C

Summary

Introduction

The study of exotic nuclear structure is at the forefront of research in modern nuclear physics [1]. The shape decoupling phenomenon, i.e., the core and the halo having different shapes, has been predicted in deformed nuclei close to the neutron drip-line [18, 19]. An apparent puzzle arises from these interplays: if the two valence neutrons occupy 2s1/2 and S2n is very small, say, from several tens keV to several hundreds keV, the radius of 22C should be much larger than the recent experimental value. The inversion of (2s1/2, 1d5/2), together with deformation effects, results in a shrinkage in the halo and a quenched shell gap at N = 16 in 22C, resolving the puzzles concerning the radius and halo configuration in this exotic nucleus. We predict that the core of 22C is oblate but the halo is prolate, adding one more candidate of deformed halo nuclei with shape decoupling effects

The DRHBc model

Results and discussions

Conclusions