Spin-Flip And Non Spin-Flip Excitations In The (Li-7,Be-9) Reaction

Spin-flip (DELTA-S = 1) and non spin-flip (DELTA-S = 0) excitations were investigated in the (Li-7, Be-7) reactions on C-12 and Si-28 at E(L) = 26 MeV/A and theta(L) = 0-degrees by measuring separately the (Li-7, Be-7(g.s.)) and (Li-7, Be-7(0.43MeV)) reaction channels with the Be-7-gamma coincidence technique. For both C-12 and Si-28, the giant dipole resonance (GDR) is clearly identified in the DELTA-S = 0 spectrum, and its strength distribution is in good agreement with that observed by the photonuclear reaction. In C-12, the 1- and 2- components of the spin-dipole resonance (SDR) are also observed in the DELTA-S = 1 spectrum. Not only the magnitudes but also the shapes of the GDR and 1- SDR are found to be very similar in C-12. On the other hand, in Si-28, though a possible 2- component of the SDR is observed, the 1- SDR is not clearly identified as a resonance. Beyond the excitation energy of the GDR for both C-12 and Si-28, DELTA-S = 0 cross sections are enhanced relative to DELTA-S = 1 ones, which suggests excitation of isovector giant resonances at 2hBAR-omega. In addition, a possible isovector octupole resonance at 1hBAR-omega was observed in the DELTA-S = 0 spectrum of Si-28.