Purpose: The neutron-rich nucleus 29Ne, located in the N = 20 “island of inversion,” challenges traditional shell-model predictions by exhibiting a ground-state valence neutron configuration dominated by the 2p3/2 orbital instead of the expected 1f7/2 orbital. This study aims to unravel the mechanisms behind this shell inversion and explore the potential halo structure in 29Ne, leveraging the interplay between weak binding, deformation, and low-l orbital occupancy.Methods: We employ the complex-momentum representation (CMR) method within a relativistic framework, combining relativistic mean-field (RMF) theory with Woods-Saxon potentials to describe bound states, resonances, and continuum states. The model incorporates quadrupole deformation (β2) to analyze single-particle energy evolution, orbital mixing, and radial density distributions. Key parameters are calibrated to experimental data, including binding energies and neutron separation energies.Key Results:1. Shell Inversion: In the spherical limit (β2 = 0), the 2p1/2 and 2p3/2 orbitals drop below the 1f7/2 orbital, confirming the collapse of the N = 20 shell gap (see Figure below).2. Deformation-Driven Halo: For β2 ≥ 0.58, the valence neutron occupies the 3/2321 orbital (derived from 1f7/2), but with 68% p3/2 components due to strong l-mixing. This orbital exhibits a diffuse radial density distribution, signaling a halo structure.3. Experimental Consistency: The predicted ground-state spin-parity (3/2-) and low separation energy (∼1 MeV) align with measurements, supporting 29Ne as a deformation-induced halo candidate.Conclusions: The study demonstrates that 29Ne’s anomalous structure arises from the synergy of p-wave dominance and quadrupole deformation, which reduces centrifugal barriers and enhances spatial dispersion. The CMR method provides a unified description of bound and resonant states, offering new insights into the island of inversion and halo formation. Future work will incorporate pairing correlations and experimental validation of density distributions.Significance: This work advances the understanding of exotic nuclear structures near drip lines and highlights the role of deformation in halo phenomena, with implications for future experiments probing neutron-rich nuclei.
Xinghao et al. (Wed,) studied this question.