Dipole excitation of ${}^6$Li and ${}^9$Be studied with an extended quantum molecular dynamics model

Abstract

The $\alpha$ (${}^4$He) - clustering structure is a common phenomenon in light nuclei due to the decreasing contribution of mean field in few-body system. In this work we presented calculations of giant dipole resonance (GDR) excitations for two non $\alpha$-conjugate light nuclei, namely ${}^6$Li and ${}^9$Be, within a framework of an extended quantum molecular dynamics model. For ${}^6$Li, we investigated the GDR spectra from the two-body clustering structure with $\alpha$ + deuteron as well as the three-body structure with $\alpha$ + $n$ + $p$, and found that the major $\alpha$-clustering contribution on the GDR peak is located at around 31 MeV, while the resonance contributions between clusters, namely $\alpha$ and deuteron or ($n$ + $p$), are located on the lower energy side, which can be regarded as pygmy dipole resonance (PDR). For ${}^9$Be, a mixture configuration contribution for the Chain-like structure and Borromean-like structure of the $\alpha$ + n + $\alpha$ configuration can somehow explain its GDR results.

Comments: 8 pages, 5 figures