Proton halo structures and 22Al

TL;DR

This study uses relativistic density functional theory to investigate whether the proton-rich nucleus 22Al exhibits a halo structure, concluding that its wave function and density distribution do not support halo formation.

Contribution

It provides a detailed theoretical analysis of 22Al's structure using two different functional parameterizations, including effects of pairing, deformation, and the continuum.

Findings

22Al's valence proton is loosely bound but does not form a halo.

Wave function mainly consists of l=2 components, disfavoring halo formation.

Density distributions show no signs of exotic halo structures.

Abstract

Inspired by the recent debate as to whether the proton drip-line nucleus 22Al demonstrates a halo structure in its ground state and in order to assess such a possibility, we have analyzed theoretical results obtained within the relativistic density functional theory in 22Al and in a number of neighboring nuclei especially along isotopic, isotonic, and isobaric chains. The theory includes self-consistently the effects of pairing, deformation and the continuum. We employ two different functional parameterizations, PC-F1 and PC-PK1. Although the valence proton of the 22Al nucleus is found very loosely bound, in concordance with experimental data, its spatial distribution is found to hardly penetrate the potential barrier. Its wave function is found to consist predominately of l=2 components, for which halo formation is disfavored. Comparisons with results for isobars reveal a somewhat more extended density distribution than that of the stable or neutron-rich counterparts, but comparisons along isotopic, isotonic, and isobaric chains reveal no discontinuities in size evolution, which, if present, might have signaled exotic structures.