GIANT-RESONANCES OF LIGHT NEUTRON-RICH NUCLEI

A large-scale shell model taking the configuration space up to 3 h-omega is applied to the study of giant dipole resonances of neutron-rich nuclei Li-11 and Be-11. The dipole states excited by the operator rY1-tau-z are studied in Li-11, while the charge-exchange strengths excited by rY1-tau + 1 and r[Y1-sigma](1)tau + 1 operators are discussed in Be-11. The strength distributions of these resonances concentrate at much lower excitation energies as compared to the systematics of other nuclei because of the small energy gap between 0p and 0d1s shells. The giant resonance is predicted at around E(x) = 12 MeV in Li-11 exhausting about half of the sum-rule value. The low-energy states decoupled from the giant resonance are also found below E(x) = 1 MeV, having a significant fraction of the transition strength, because of the large neutron excess and the loosely bound single-particle state. The charge-exchange dipole strengths are also found in the energy region E(x) = 5-10 MeV above the ground state of Be-11 having large portion of the sum-rule value.