Shell-model study of electric dipole and spin-dipole strengths in Li-11

We have studied electric dipole (E1) and spin-dipole strength distribution in Li-11 by shell model calculations with halo effect. Two peaks in the E1 strength are found in the low excitation energy region below E-x = 4 MeV, w hich have almost the same energies as observed E1 peaks in the Coulomb brea kup reaction of Li-11. The calculated E1 strength up to E-x = 4 MeV exhaust about 4% of the Thomas-Reiche-Kuhn energy-weighted sum rule value. We foun d also pigmy and giant peaks in spin-dipole strengths of Li-11. Possible ex istence of double soft dipole mode and giant resonance built on the soft di pole states are investigated. (C) 2000 Elsevier Science B.V. All rights res erved.