Evolution of shell Structure and Collectivity in Neutron-Rich Nuclei

本研究旨在利用放射性离子束的二次反应来研究丰中子核的特征激发态。结果总结如下：(A)测量α诱导反应及其衰变过程的实验性能：由α非弹性散射的逆运动学测量得出的微分截面的角分布提供了关于传递角动量的信息。衰变过程的角分布提供了激发态的自旋和排列，这在直接反应理论(如DWBA)中得到了很好的再现。几十MeV的α粒子的核子剥离反应是研究奇异核中单粒子态的有力工具。(B)测量了^&lt；12&gt；Be：α非弹性散射后的H^&lt；6&gt；e+H^&lt；6&gt；e和H^&lt；4&gt；e+H^&lt；8&gt；e衰变。角分布…用扩展的多极分解方法分析了更多的微分截面和衰变过程。所推导的每个自旋的激发谱都显示了奇异团簇的候选共振结构。(C)N=8磁性在^&lt；12&gt；Be附近的消失：确定了^&lt；12&gt；Be中第二个0^&lt；+&gt；态的寿命和分支比。相对较大的EO和E2跃迁几率表明，在一个大变形的平均场中，单粒子组态的强烈混合。大的形变是由低能级的质子入侵态支持的，L在^&lt；13&gt；B中被质子转移反应填充到^&lt；12&gt；Be中。(D)丰中子氧同位素中的质子壳层结构：通过对^&lt；22&gt；O的质子转移反应研究了^&lt；23&gt；F中的质子单粒子态。核子核聚变反应的CA区：用46&gt；Ar的次级核子核子核素聚变反应测量了~&t；46&gt；Ar~+&t；9&gt；Be体系的核聚变反应。用GRAPE阵列式位置灵敏Ge探测器，用在束伽马射线能谱研究了49-51&Tt；Ti的高自旋态。发现了新的高自旋态，在N=28附近有壳隙。(F)葡萄的研究和开发：已经建立了葡萄特性的自动测量系统。发展了用于三维位置确定的数字信号处理。较少

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