Isovector giant resonances studied by the (^7Li, ^7Be-gamma) reaction

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This project aims at studying isovector giant resonances via the (7Li, 7Be) reaction at intermediate energies. The (7Li, 7Be) reaction has characteristics to separately derive spin-flip (DELTAS=1) and non spin-flip (DELTAS=0) isovector excitations by measuring gamma-rays in coincidence with 7Be-ejectiles. Measurement of both DELTAS=0 and DELTAS=1 spectra under the same kinematical condition is expected to provide direct evidence of isovector resonances with DELTAS=0 and DELTAS=1, their relative strength distribution, and nuclear spin-isospin responses.A new gamma-detector system "NYMPHS" were developed using 22 pieces of GSO scintillator. Feasibility of the NYMPHS for the 7Be-gamma coincidence was investigated in the (7Li, 7Be) reactions on 12C and 90Zr at 65 AMeV.The multi-segmented detector system showed good performance for the 7Be-gamma coincidence measurement. The 7Be gamma-ray were clearly identified by detecting its Doppler effect.We investigated nuclear spin-isospin responses in light nuclei. The (7Li, 7Be) reaction was found to predominantly proceed via one-step reaction process. From the H(7Li, 7Be)n reaction, we got an effective nuclear interaction ratio of Vsigmatau/Vtau at 65 AMeV.The ratio is very consistent with the (p, n) data. Using Vsigmatau/Vtau presently observed, we could get relative spin-stregth which reflects nuclear spin-isospin responses.We conclude that the 7Be-gamma coincidence measurement using the NYMPHS is applicable to the (7Li, 7Be) reaction from light nuclei to medium-heavy nuclei at intermediate energies. This means the (7Li, 7Be) reaction is a unique spin-probe for isovector excitations.