/ 0 50 80 57 v 1 2 7 A ug 2 00 5 Dipole resonances in light neutron - rich nuclei studied with time - dependent calculations of antisymmetrized molecular dynamics

In order to study isovector dipole response of neutron-rich nuclei, we have applied a time-dependent method of antisymmetrized molecular dynamics. The dipole resonances in Be, B and C isotopes have been investigated. In 10 Be, 15 B, 16 C, collective modes of the vibration between a core and valence neutrons cause soft resonances at the excitation energy Ex = 10 − 15 MeV below the giant dipole resonance(GDR). In 16 C, we found that a remarkable peak at Ex = 14 MeV corresponds to coherent motion of four valence neutrons against a 12 C core, while the GDR arises from the core vibration in the Ex > 20 MeV region. In 17 B and 18 C, the dipole strengths in the low energy region decline compared with those in 15 B and 16 C. We also discuss the energy weighted sum rule for the E1 transitions.