Question of low-lying intruder states in Be and neighboring nuclei

The presence of not yet detected intruder states in Be, e.g., a J52 intruder at 9 MeV excitation would affect the shape of the b-delayed a spectra of Li and B. In order to test the plausibility of this assumption, shell-model calculations with up to 4\v excitations in Be ~and up to 2\v excitations in Be! were performed. With the above restrictions on the model spaces, the calculations did not yield any low-lying intruder state in Be. Another approach—the simple deformed oscillator model with self-consistent frequencies and volume conservation—gives an intruder state in Be which is lower in energy than the above shell-model results, but its energy is still considerably higher than 9 MeV. @S0556-2813~98!07305-1#