Nilsson diagrams for light neutron-rich nuclei with weakly-bound neutrons

TL;DR

This paper uses Woods-Saxon potentials and eigenphase formalism to analyze neutron levels in light neutron-rich nuclei, revealing systematic shell structure changes and deformation preferences due to weak binding and resonances.

Contribution

It introduces a systematic analysis of one-particle neutron levels in weakly-bound nuclei using realistic potentials, highlighting differences from traditional Nilsson diagrams.

Findings

Weakly-bound neutrons favor deformation due to near-degenerate levels.

Systematic changes in shell structure linked to small orbital angular momenta.

Absence of some resonant levels compared to textbook Nilsson diagrams.

Abstract

Using Woods-Saxon potentials and the eigenphase formalism for one-particle resonances, one-particle bound and resonant levels for neutrons as a function of quadrupole deformation are presented, which are supposed to be useful for the interpretation of spectroscopic properties of some light neutron-rich nuclei with weakly-bound neutrons. Compared with Nilsson diagrams in text books which are constructed using modified oscillator potentials, we point out a systematic change of the shell structure in connection with both weakly-bound and resonant one-particle levels related to small orbital angular momenta $\ell$. Then, it is seen that weakly-bound neutrons in nuclei such as $^{15-19}$C and $^{33-37}$Mg may prefer to being deformed as a result of Jahn-Teller effect, due to the near degeneracy of the 1d$_{5/2}$-2s$_{1/2}$ levels and the 1f$_{7/2}$-2p$_{3/2}$ levels in the spherical potential, respectively. Furthermore, the absence of some one-particle resonant levels compared with the Nilsson diagrams in text books is illustrated.