Dipole Excitation of α Clusters in L6i and L7i

Dipole excitations in highly excited energy regions of ${}^{6}\mathrm{He}$ and ${}^{7}\mathrm{He}$ nuclei were investigated via the ( ${}^{7}\mathrm{Li}{,}^{7}\mathrm{Be}$) reaction with an incident energy of $65A\mathrm{MeV}$ at forward scattering angles. The resonances at $Q\ensuremath{\simeq}\ensuremath{-}30\mathrm{MeV}$ observed commonly for both ${}^{6}\mathrm{Li}$ and ${}^{7}\mathrm{Li}$ targets were found to be excited via both spin-flip and spin-nonflip transitions with $\ensuremath{\Delta}L\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$. Based on the observed excitation energy, width, and cross section of each resonance, the relevant resonances are inferred to be analogs of the dipole resonances of $\ensuremath{\alpha}$ clusters in the ${}^{6}\mathrm{Li}$ and ${}^{7}\mathrm{Li}$ nuclei.