Question of low-lying intruder states in8Beand neighboring nuclei

Abstract

The presence of not yet detected intruder states in ${}^{8}\mathrm{Be},$ e.g., a ${J=2}^{+}$ intruder at 9 MeV excitation would affect the shape of the ${\ensuremath{\beta}}^{\ensuremath{\mp}}$-delayed $\ensuremath{\alpha}$ spectra of ${}^{8}\mathrm{Li}$ and ${}^{8}\mathrm{B}.$ In order to test the plausibility of this assumption, shell-model calculations with up to $4\ensuremath{\Elzxh}\ensuremath{\omega}$ excitations in ${}^{8}\mathrm{Be}$ (and up to $2\ensuremath{\Elzxh}\ensuremath{\omega}$ excitations in ${}^{10}\mathrm{Be}$) were performed. With the above restrictions on the model spaces, the calculations did not yield any low-lying intruder state in ${}^{8}\mathrm{Be}.$ Another approach---the simple deformed oscillator model with self-consistent frequencies and volume conservation---gives an intruder state in ${}^{8}\mathrm{Be}$ which is lower in energy than the above shell-model results, but its energy is still considerably higher than 9 MeV.