Unbound spectra of neutron-rich oxygen isotopes predicted by the Gamow shell model

The Gamow shell model has shown to efficiently describe weakly bound and unbound nuclear systems, as internucleon correlations and continuum coupling are both taken into account in this model. In the present work, we study neutron-dripline oxygen isotopes. It is hereby demonstrated that the presence of continuum coupling is important for the description of oxygen isotopes at dripline, and especially to assess the eventual bound or unbound character of ${}^{28}\mathrm{O}$. Our results suggest that the ground state of ${}^{28}\mathrm{O}$ is weakly unbound and is similar to the narrow resonant ${}^{26}\mathrm{O}$ ground state. Predictions of weakly bound and resonance excited states in ${}^{24\text{–}26}\mathrm{O}$ are also provided. The asymptotes of the studied many-body states are analyzed via one-body densities, whereby the different radial properties of well bound, loosely bound, resonance states are clearly depicted.

Figure 1

Energies of ground states in ${}^{24\text{–}28}\mathrm{O}$, calculated by GSM within the $sdpf$ (upper) and $sd$ (lower) model spaces, using the EFT(318), EFT(356), EFT(390), EFT(436), and FHT interactions, with $A$-independence ($A$-indep) or $A$-dependence ($A$-dep) (see text for definitions). Results are compared with data available [5, 49], represented by a star. The data for ${}^{25,26}\mathrm{O}$ and ${}^{27,28}\mathrm{O}$ are taken from the experiment [5] and evaluations given in AME2016 [49], respectively.

Figure 2

Radial one-body density multiplied by radius squared, denoted by $r^2\rho \left(r\right)$, of the ground states of oxygen neutron-rich ${}^{18\text{–}28}\mathrm{O}$ isotopes as a function of the radius $r$ (in fm).

Figure 3

GSM calculations of low-lying positive-parity states of ${}^{23\text{–}26}\mathrm{O}$ using the EFT(356) interaction, along with experimental data [5, 37]. Resonance state is indicated with a green shade, and its width is written above (or below) the level in keV.

Figure 4

Similar to Fig. 2, but for the excited states (and also the ground states in ${}^{25,26}\mathrm{O}$ for comparison) of the neutron-dripline oxygen isotopes calculated with GSM using the EFT(356) interaction.