Analogs of the giant dipole and spin-dipole resonances in 4He and in a clusters of 6,7Li studied by the 4He,6,7Li(7Li,7Beγ) reactions

We studied analogs of the giant dipole resonance (GDR) and spin-dipole resonance (SDR) in 4 He and in the a clusters of 6,7 Li via the ( 7 Li, 7 Beγ) reactions on 4 He, 6 Li, and 7 Li at an incident energy of 455 MeV and at a scattering angle of 0° by measuring spin-nonflip and spin-flip spectra. The reaction Q-values for the analogs of the GDR and SDR in the a clusters of 6,7 Li were found to be more negative than those in 4 He by 2.0 ± 0.5 MeV. The ratios of the cross section for the analog of the GDR to that for the analog of the SDR in 4 He and in the a clusters of 6 Li and 7 Li were found to be the same within errors, 0.5 ± 0.1. The cross sections for the analogs of the GDR as well as those for the analogs of the SDR in the a clusters of 6,7 Li were 0.6∼0.8 times smaller than those in 4 He. These results suggest that excitations of a clusters embedded in nuclei are suppressed as compared with excitations of free a particles.