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

We have studied electric dipole (E1) and spin-dipole strength distribution in 11Li by shell model calculations with halo effect. Two peaks in the E1 strength are found in the low excitation energy region below Ex=4 MeV, which have almost the same energies as observed E1 peaks in the Coulomb breakup reaction of 11Li. The calculated E1 strength up to Ex=4 MeV exhaust about 4% of the Thomas–Reiche–Kuhn energy-weighted sum rule value. We found also pigmy and giant peaks in spin-dipole strengths of 11Li. Possible existence of double soft dipole mode and giant resonance built on the soft dipole states are investigated.