The Question of Low-Lying Intruder States in ${}^{8}Be$ and Neighboring Nuclei

Abstract

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

Comments: 16 pages (RevTeX), 1 PS figure. To appear in Phys. Rev. C