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

Abstract

The $α$ ($^4$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 $α$-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 $α$ + deuteron as well as the three-body structure with $α$ + $n$ + $p$, and found that the major $α$-clustering contribution on the GDR peak is located at around 31 MeV, while the resonance contributions between clusters, namely $α$ 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 $α$ + n + $α$ configuration can somehow explain its GDR results.