Exploring the halo character and dipole response in the dripline nucleus F 31

Background: Lying at the lower edge of the "island of inversion," neutron-rich fluorine isotopes ( 29 – 31 F ) provide a curious case to study the configuration mixing in this part of the nuclear landscape. Recent studies have suggested that a prospective two-neutron halo in the dripline nucleus 31 F could be linked to the occupancy of the p f intruder configurations. Purpose: Focusing on configuration mixing, matter radii, and neutron-neutron ( n n ) correlations in the ground state of 31 F , we explore various scenarios to analyze its possible halo nature as well as the low-lying electric dipole ( E 1 ) response within a three-body approach. Method: We use an analytical, transformed harmonic oscillator basis under the aegis of a hyperspherical formalism to construct the ground-state three-body wave function of 31 F . The n n interaction is defined by the Gogny-Pires-Tourreil potential that includes the central, spin-orbit, and tensor terms, while the different two-body potentials to describe the core + n subsystems are constrained by the different possible scenarios considered. Results: The 31 F ground-state configuration mixing and its matter radius are computed for different choices of the 30 F structure coupled to the valence neutron. The admixture of p 3 / 2 , d 3 / 2 , and f 7 / 2 components is found to play an important role, favoring the dominance of inverted configurations with dineutron spreads for two-neutron halo formation. The increase in matter radius with respect to the core radius, Δ r ≳ 0.30 fm and the dipole distributions along with the integrated B ( E 1 ) strengths of ⩾ 2.6 e 2 fm 2 are large enough to be compatible with other two-neutron halo nuclei.