Studies Of Bubble Structure Around ⁴⁶Arwithin Relativistic Hartree-Fock-Bogoliubov Theory

In recent decades, with the rapid development of Radioactive Ion Beam (RIB) facilities, the structural properties and novel phenomenon of exotic nuclei have drawn more and more attentions. As a kind of exotic nuclei, the bubble structure in nuclei have became a hot topic in recent research. Different from the stable nucleus, the central densities of bubble nuclei are highly depressed. In the medium mass region of the nuclide chart, some nuclei, e.g.,34Si,46Ar, even some superheavy nuclei were predicted as candidates of possible bubble nuclei.In this work, we have studied the charge density distributions of argon iso-topes and N=28 isotones by relativistic Hartree-Fock-Bogoliubov (RHFB) with PKA1, PKO1 and PK03 and relativistic Hartree-Bogoliubov (RHB) with PKD-D and DD-ME2, explored the physical mechanism on the formation of proton bubble structure. In this paper, we first calculate the nuclear binding energy and rms charge radius of argon isotopes,and it is found that PKA1 can provide the best description on rms charge radius. Then we calculated the charge density distributions of argon isotopes, in which the central depressions of charge den-sity of argon isotopes are not reproduced by PKA1. From the analysis of shell structure of argon isotopes, we found that PKA1 do not support the inversion of proton πs1/2 and π1d3/2 orbits, in which the 2s1/2 orbit was unoccupied, thus inhibiting the formation of proton bubble structure. In fact this conclusion is consistent with the presence of Z=16 shell in this area revealed by the relevant experimental data.Similar to the Ar isotope isotopes, we studied the charge density distri-butions of N=28 isotones. It is shown that the central densities are highly de-pressed in 40Mg and 42Si with the calculation with PKA1. And Only PKA1 can reproduce the near degeneracy of π2s1/2 and π1d3/2 orbits in 48Ca, thus the description of PKA1 is more reasonable. Along the N=28 isotones, we found that the Z=14 shell is still persistent with decreasing proton number, prevent the valence proton occupy the π2s1/2 orbit,finally leading to the highly depressed central densities of 42Si and 40Mg. Thus theory have predicted that the bubble structure may exist in 42Si and 40Mg.