Electromagnetic nuclear moments around neutron magic number 20 and 28

本研究的目的是通过测量电磁核矩来研究中子幻数N = 20和28附近远富中子核的结构。在N = 20的核区，在法国GANIL测量了33Al的基态电四极矩(Q)。得到的Q值与常规sd模型空间内的单粒子值和壳层模型计算结果有较大的向外差异，表明N = 20的壳层闭合受到侵蚀。对于N = 28区域，在RIKEN RIBF设备上测量了43S在320 keV下的Q矩。数据表明，尽管有水平反转，但43S形变是温和的，表明基态变形强烈，低洼状态形状共存。本研究提出了一种利用离子光学技术的动量色散匹配相结合的两步破碎反应制备自旋定向RI光束的方法。

The purpose of this study is to investigate the structure of far neutron-rich nuclei around neutron magic number N = 20 and 28 through the measurement of electromagnetic nuclear moments. In the nuclear region of N = 20, a ground-state electric quadrupole (Q) moment of 33Al was measured at GANIL, France. The obtained Q shows a large outward discrepancy from a single particle value and shell model calculations within the conventional sd model space, suggesting the erosion of N = 20 shell closure. For the N = 28 region, the Q moment of the isomeric state of 43S at 320 keV was measured at the RIKEN RIBF facility. The data shows that the 43S deformation is modest in spite of the level inversion, suggesting a strong deformation of the ground state and a shape coexistence in the low-lying states. In this study, a noble method to produce spin-aligned RI beams utilizing two-step fragmentation reaction combined with momentum dispersion-matching of the ion optics technique has been developed.