Cluster-orbital shell model and its application to the He isotopes

A model is proposed in which we take full advantage of both the shell and cluster models in order to describe a system of valence nucleons weakly coupled to a core. This is realized by introducing radius vectors of the valence nucleons relative to the core, new coordinates of independent particle nature. The model is applied to the neutron-rich He isotopes, ${}_{}{}^{6\mathrm{-}8}{}_{}{}^{}\mathrm{He}$, with reasonable success.