Evolution of shell Structure and Collectivity in Neutron-Rich Nuclei

利用放射性离子束的次级反应研究丰中子核的特征激发态。（a）测量α诱导反应及其衰变过程的实验性能：通过α非弹性散射的逆运动学测量推导出的微分截面的角分布提供了关于转移角动量的信息。衰变过程的角分布提供了激发态的自旋和排列，这可以通过直接反应理论如DWBA很好地再现。几十MeV的α粒子核子剥离反应是研究奇异核单粒子态的有力工具。(b)本文测量了^<12>Be：α非弹性散射中的团簇态<12>H^<6>e+H^<6>e和H^<4>e+H^<8>e衰变。角分布 ...更多信息 的微分截面和衰变过程进行了分析。每个自旋的激发谱都显示了共振结构，这些共振结构是奇异团簇态的候选者。(c)N=8幻数在^ Be附近的消失<12>：测定了^ Be中第二个0^&lt;+&gt;态的寿命和分支比<12>。相对较大的EO和E2跃迁概率表明在一个很大程度上变形的平均场的单粒子粒子配置的强混合。这种大变形是由质子向^ Be的转移反应所引起的^ B中1/2^&lt;+&gt;的低位质子入侵态所支持<13><12>的。(d)丰中子氧同位素中的质子壳层结构：<23>通过质子向^ O的转移反应研究了^ F中<22>的质子单粒子态。自旋轨道分裂的演化作为中子占据数的函数已被证明。(e)利用<48>RI束聚变反应在^ Ca区产生高自旋态：<46><9>用^ Ar的次级RI束测量了^ Ar+^ Be系统在3-7 MeV/核子<46>的聚变反应。利用<49-51>位置灵敏Ge探测器组成的GRAPE阵列，用在束γ谱研究了Ti中的高自旋态。发现了新的高自旋态，在N=28附近显示出壳层间隙。(f)GRAPE的研究与开发：建立了GRAPE自动测试系统。用于三维位置确定的数字信号处理已经被开发。少

The present research aims at studying characteristic excited states in neutron-rich nuclei by using secondary reactions of radioactive ion (RI) beams. The followings are summary of the results:(a) Experimental performance in measurement of alpha-induced reactions and their decay process : Angular distribution of the differential cross sections deduced by inverse-kinematics measurement of alpha inelastic scattering provides information on the transferred angular momentum. The angular distribution of the decay process provides the spin and the alignment of the excited state, which is well reproduced by direct reaction theory such as DWBA. The nucleon stripping reactions from the alpha particle at several tens of MeV have been studied as powerful tool for the investigation of the single-particle states in exotic nuclei.(b) Cluster states in ^<12>Be : Alpha inelastic scattering on ^<12>Be followed by the H^<6>e+H^<6>e and the H^<4>e+H^<8>e decay has been measured. The angular distributions … More of the differential cross sections and the decay process have been analyzed by an extended multipole decomposition method. The deduced excitation spectrum for each spin shows resonance structures which are candidates of exotic cluster states.(c) Disappearance of N=8 magicity around ^<12>Be : The lifetime and branching ratio of the second 0^<+> state in ^<12>Be have been determined. Relatively large EO and E2 transition probabilities indicate a strong mixing of single-particle particle configurations in a largely deformed mean field. The large deformation is supported by a low-lying proton intruder state with l/2^<+> in ^<13>B populated by the proton-transfer reaction to ^<12>Be.(d) Proton shell structure in neutron-rich Oxygen isotopes : Proton single particle states in ^<23>F have been studied by the proton transfer reaction to ^<22>O. Evolution of the spin-orbit splitting as a function of the neutron occupation number has been demonstrated.(e) High spin states in ^<48>Ca region by fusion reactions of RI beams : Fusion reaction of the ^<46>Ar+^<9>Be system has been measured at 3-7 MeV per nucleon by the secondary RI beam of ^<46>Ar. High spin states in ^<49-51>Ti have been studied by in-beam gamma-ray spectroscopy using the GRAPE array consisting of position-sensitive Ge detectors. New high-spin states have been found showing a shell gap around N=28.(f) Research and Development of GRAPE : Automatic measurement system for characterizing the GRAPE has been constructed. Digital signal processing for 3-dimensional position determination has been developed. Less