Low-energy dipole excitation modes in ${}^{10}$Be

Abstract

Low-energy dipole excitations in ${}^{10}$Be were investigated based on the generator coordinate method with $\alpha +{}^6$He and $\alpha +\alpha +2n$ cluster models. We obtained three $1^{-}$ states in $E_x<15$~MeV, which show different characters in the $E1$, compressive dipole, and toroidal dipole transition strengths. We found the strong toroidal dipole transition in the $1_1^{-}$ state, remarkable $E1$ strength in the $1_2^{-}$ state, and the strong $E1$ and compressive dipole strength in the $1_3^{-}$ state. The $1_1^{-}$ is described by the $\alpha +{}^6$He cluster structure, where as the $1_2^{-}$ and $1_3^{-}$ states are understood by three-body excitations of the $\alpha +\alpha +2n$ clustering.

Comments: 20 pages, 8 figures