Two-neutron halo structure of ${}^{31}$F and a novel pairing anti-halo effect

Abstract

Background: A newly identified dripline nucleus ${}^{31}$F offers a unique opportunity to study the two-neutron ($2n$) correlation at the east shore of the island of inversion where the $N=28$ shell closure is lost. Purpose: We aim to present the first three-body theoretical results for the radius and total reaction cross sections of ${}^{31}$F. This will further help to investigate how the pairing and breakdown of the $N=28$ shell closure influence the formation of the $2n$-halo structure and the anti-halo effect in this mass region. Methods: A ${}^{29}$F$+n+n$ three-body system is described by the cluster orbital shell model, and its total reaction cross section is calculated by the Glauber theory. Results: Our three-body calculations predict 3.48-3.70 fm for the root-mean-square radius of ${}^{31}$F, which corresponds to the total reaction cross section of 1530 (1410)-1640 (1500) mb for a carbon target at 240 (900) MeV/nucleon. The binding mechanism and halo formation in ${}^{31}$F are discussed. Conclusions: The present study suggests a novel anti-halo effect in this mass region: When the pairing overcome the energy gap between the $p_{3/2}$ and $f_{7/2}$ orbits, the inversion of the occupation number of these orbits takes place, and it diminishes the $2n$-halo structure.

6 pages, 3 figures

References in corpus (5)

• Recent development of complex scaling method for many-body resonances and continua in light nuclei
• ${}^{22}$C: $S$-Wave Two-Neutron Halo
• Two-neutron halo structure of ${}^{31}$F
• Exploring two-neutron halo formation in the ground-state of ${}^{29}$F within a three-body model
• Precise comparison of the Gaussian expansion method and the Gamow shell model

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• Utility of antiproton-nucleus scattering for probing nuclear surface density distributions
• Two-cluster approach to the properties of one- and two-neutron-halo nuclei
• Deformation, halo, and bubble structure: A paradigm shift of exotic phenomena in light to medium mass nuclei
• Two-neutron halo structure and anti-halo effect in 31F