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

本项目旨在研究中能级（7Li, 7Be）反应的等矢量巨共振。（7Li, 7Be）反应具有通过测量与7Be弹射体重合的伽马射线分别导出自旋翻转（DELTAS=1）和非自旋翻转（DELTAS=0）等矢量激发的特点。在相同的运动学条件下测量δ tas =0和δ tas =1的光谱，有望为δ tas =0和δ tas =1的等矢量共振、它们的相对强度分布和核自旋-同位旋响应提供直接证据。利用22片GSO闪烁体研制了一种新的伽玛探测系统“NYMPHS”。在65 AMeV下12C和90Zr上的（7Li, 7Be）反应中，研究了NYMPHS对7Be- γ重合的可行性。多段探测器系统在7be - γ符合测量中表现出良好的性能。通过检测其多普勒效应，可以清楚地识别出7Be伽马射线。我们研究了轻核中的核自旋-同位旋反应。发现（7Li, 7Be）反应主要通过一步反应进行。从H(7Li, 7Be)n反应中，我们得到了65 AMeV下的有效核相互作用比Vsigmatau/Vtau。该比率与（p, n）数据非常一致。利用目前观测到的Vsigmatau/Vtau，我们可以得到反映核自旋-同位旋响应的相对自旋强度。我们的结论是，使用NYMPHS的7Be- γ符合测量适用于（7Li, 7Be）轻核到中重核的中能反应。这意味着（7Li, 7Be）反应是一个独特的自旋探针，用于等矢量激发。

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.