Nuclear Binding Mechanism and Structure of Neutron-Rich Be and B Isotopes by Molecular-Orbital Model

The neutron-rich (n-rich) Be and B isotopes are investigated by a molecular-orbital model, which is constructed on the (l-(l cluster structure of 8Be. Total energies of the ground states and some excited states are calculated with a densityand starting-energy-dependent effective interaction, including rearrangement effects. The absolute values of the binding energies and the general trend of their isotope dependence are well reproduced for nuclei up to l6Be and 17B. I t is found that not only the densityand starting-energy-dependence of the effective interaction, but also the spin-orbit potential has important effects on the particle stability of n-rich nuclei, especially, extremely n-rich nuclei. It is also found that the (l-(l cluster structure as a core persists in these isotopes, especially in non-normal parity states. The spin-orbit potential reduces clustering in nuclei up to the neutron-closed shell nucleus and, on the other hand, it enhances clustering in extremely n-rich nuclei. Our model easily reproduces the non-normal parity states of 'Be 0/21+: 1.68 MeV) and ilBe (l/2": ground state) in very low energy regions and is useful for explanation of low-lying level structure of Be and B isotopes.