Structure and reactions of theBe12,14nuclei

The phenomenon of s-wave intruder orbits is examined for the ${}_{}{}^{12}{}_{}{}^{}\mathrm{Be}$ and ${}_{}{}^{14}{}_{}{}^{}\mathrm{Be}$ isotopes. Although ${}_{}{}^{11}{}_{}{}^{}\mathrm{Be}$ has an s-wave ground state, a three-body model of two neutrons + ${}_{}{}^{10}{}_{}{}^{}\mathrm{Be}$ can only reproduce the properties of ${}_{}{}^{12}{}_{}{}^{}\mathrm{Be}$ if the valence neutrons occupy mainly the (${\mathit{p}}_{1/2}$ ${)}^2$ configuration with about 25% admixture of (sd${)}^2$ configurations. For ${}_{}{}^{14}{}_{}{}^{}\mathrm{Be}$, the possibility of low-lying s-wave states in ${}_{}{}^{13}{}_{}{}^{}\mathrm{Be}$ means that a wide range of models are compatible with the existing radius and momentum measurements, though some s admixture is necessary for binding. We show which kinds of momentum and Coulomb breakup measurements will be necessary to elucidate the structure of the ${}_{}{}^{14}{}_{}{}^{}\mathrm{Be}$ halo. © 1996 The American Physical Society.