Structure of nuclei far from stability

在58Ni和100Sn之间的N=Z核区域由于形状的显著差异而成为理论和实验研究的热点。由于占据了相同的形变驱动轨道，随着质量的增加，这些原子核中的基态形状预计将从球形演化到三轴、扁平、长方形，然后回到球形。此外，激发能级可以具有与基态显著不同的结构。例如，在68Se和72Kr中，扁平形变的基态带被报道与长形变的激发带共存。这一区域低激发态激发能的变化通常被用来分析远离双魔56Ni核的结构的演化。然而，电磁转换率被认为提供了更灵敏的集体和形变探测。当前建议的目标是启动一项研究计划，解决N=Z线上重核中的电磁跃迁速率，目的是测量四极形变和三轴，以及识别形状转变和形状共存的特征。选择的实验方法分别是寿命大于1皮秒和小于1皮秒的反冲距离法(RDM)和多普勒频移衰减法(DSAM)。在复合核反应之后将填充感兴趣的状态；实验装置将包括老虎阵列，与CSI带电粒子探测器阵列一起工作的老虎集成柱塞(TIP)设备，以及未来的中子探测器的下降阵列。第一个实验将解决68Se和72Kr分别通过40Ca(36Ar，2α)和40Ca(40Ca，2α)反应填充的形状共存问题。

The region of N=Z nuclei between 58Ni and 100Sn became the subject of vigorous theoretical and experimental studies due to a remarkable diversity of shapes. Ground-state shapes in these nuclei are predicted to evolve from spherical to triaxial, oblate, prolate, and back to spherical as the mass increases due to the occupation of identical deformation-driving orbitals. Moreover, the excited levels can have significantly different structure than the ground state. For example, in 68Se and 72Kr the oblate-deformed ground state band is reported to coexist with a prolate-deformed excited band. Variations in the excitation energy of low-lying states in this region are often used to analyze the evolution of structure away from the doubly-magic 56Ni core. However, electromagnetic transition rates are recognized as providing a more sensitive probe of collectivity and deformation. The goal of the current proposal is to initiate a program of studies addressing electromagnetic transition rates in heavy nuclei along the N=Z line aimed at the measurements of quadrupole deformation and triaxiality, as well as the identification of signatures of shape transitions and shape coexistence. The experimental methods of choice are the Recoil Distance Method (RDM) and the Doppler Shift Attenuation Method (DSAM) for lifetimes longer and shorter then 1 picosecond, respectively. States of interest will be populated following compound nucleus reactions; the experimental setup will include the TIGRESS array, the TIGRESS integrated plunger (TIP) device working in conjunction with an array of CsI charged-particle detectors, and, in the future, the DESCANT array of neutron detectors. The first experiments will address shape coexistence in 68Se and 72Kr populated via the 40Ca(36Ar,2alpha) and 40Ca(40Ca,2alpha) reactions, respectively.