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تسجيل مستخدم جديدExploring the halo character and dipole response in the dripline nucleus $^{31}$F
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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 $pf$ intruder configurations. Focusing on configuration mixing, matter radii and neutron-neutron ($nn$) 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. 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 $^{31}$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, favouring the dominance of inverted configurations with dineutron spreads for two-neutron halo formation. The increase in matter radius with respect to the core radius, $Delta r geqslant$ 0.30 fm and the dipole distributions along with the integrated $B(E1)$ strengths of $geqslant$ 2.6 $e^2$fm$^2$ are large enough to be compatible with other two-neutron halo nuclei. Three-body results for $^{31}$F indicate a large spatial extension in its ground state due to the inversion of the energy levels of the normal shell model scheme. The increase is augmented by and is proportional to the extent of the $p_{3/2}$ component in the wave function. Additionally, the enhanced dipole distributions and large $B(E1)$ strengths all point to the two-neutron halo character of $^{31}$F.
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The neutron-rich $^{28,29}$F isotopes have been recently studied via knockout and interaction cross-section measurements. The $2n$ halo in $^{29}$F has been linked to the occupancy of $pf$ intruder configurations. We investigate bound and continuum s
tates in $^{29}$F, focusing on the $E1$ response of low-lying excitations and the effect of dipole couplings on nuclear reactions. $^{29}text{F}$ ($^{27}text{F}+n+n$) wave functions are built within the hyperspherical harmonics formalism, and reaction cross sections are calculated using the Glauber theory. Continuum states and $B(E1)$ transition probabilities are described in a pseudostate approach using the analytical THO basis. The corresponding structure form factors are used in CDCC calculations to describe low-energy scattering. Parity inversion in $^{28}$F leads to a $^{29}$F ground state characterized by 57.5% of $(p_{3/2})^2$ intruder components, a strong dineutron configuration, and an increase of the matter radius with respect to the core radius of $Delta R=0.20$ fm. Glauber-model calculations for a carbon target at 240 MeV/nucleon provide a total reaction cross section of 1370 mb, in agreement with recent data. The model produces also a barely bound excited state corresponding to a quadrupole excitation. $B(E1)$ calculations into the continuum yield a total strength of 1.59 e$^2$fm$^2$ up to 6 MeV, and the $E1$ distribution exhibits a resonance at $approx$ 0.85 MeV. Results using a standard shell-model order for $^{28}$F lead to a considerable reduction of the $B(E1)$ distribution. The four-body CDCC calculations for $^{29}text{F}+^{120}text{Sn}$ around the Coulomb barrier are dominated by dipole couplings, which totally cancel the Fresnel peak in the elastic cross section. These results are consistent with a two-neutron halo and may guide future experimental campaigns.
Background$colon$ The $^{29}$F system is located at the lower-N boundary of the island of inversion and is an exotic, weakly bound system. Little is known about this system beyond its two-neutron separation energy ($S_{2n}$) with large uncertainties.
A similar situation is found for the low-lying spectrum of its unbound binary subsystem $^{28}$F. Purpose$colon$ To investigate the configuration mixing, matter radius and neutron-neutron correlations in the ground state of $^{29}$F within a three-body model, exploring the possibility of $^{29}$F to be a two-neutron halo nucleus. Method$colon$ The $^{29}$F ground-state wave function is built within the hyperspherical formalism by using an analytical transformed harmonic oscillator basis. The Gogny-Pires-Tourreil (GPT) nn interaction with central, spin-orbit and tensor terms is employed in the present calculations, together with different core$+n$ potentials constrained by the available experimental information on $^{28}$F. Results$colon$ The $^{29}$F ground-state configuration mixing and its matter radius are computed for different choices of the $^{28}$F structure and $S_{2n}$ value. The admixture of d-waves with pf components are found to play an important role, favoring the dominance of dineutron configurations in the wave function. Our computed radii show a mild sensitivity to the $^{27}$F$+n$ potential and $S_{2n}$ values. The relative increase of the matter radius with respect to the $^{27}$F core lies in the range 0.1-0.4 fm depending upon these choices. Conclusions$colon$ Our three-body results for $^{29}$F indicate the presence of a moderate halo structure in its ground state, which is enhanced by larger intruder components. This finding calls for an experimental confirmation.
We apply the Gamow shell model to study $^{25-31}$F isotopes. As both inter-nucleon correlations and continuum coupling are properly treated therein, the structure shape of $^{31}$F at large distance can be analyzed precisely. For this, one-nucleon d
ensities, root-mean square radii and correlation densities are calculated in neutron-rich fluorine isotopes. It is then suggested that $^{31}$F exhibits a two-neutron halo structure, built from both continuum coupling and nucleon-nucleon correlations.
Halo is one of the most interesting phenomena in exotic nuclei especially for $^{31}$Ne, which is deemed to be a halo nucleus formed by a $p-$wave resonance. However, the theoretical calculations dont suggest a $p-$wave resonance using the scattering
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