Dipole resonances in light neutron-rich nuclei studied with time-dependent calculations of antisymmetrized molecular dynamics

Abstract

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 $E_x=10-15$ MeV below the giant dipole resonance(GDR). In ${}^{16}$C, we found that a remarkable peak at $E_x=14$ MeV corresponds to coherent motion of four valence neutrons against a ${}^{12}$C core, while the GDR arises from the core vibration in the $E_x>20$ 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.

Comments: 12 figures, submitted to Phys. Rev. C