Structure of nuclei far from stability

在58Ni和100Sn之间的N=Z核区域，由于其形状的显著多样性，成为理论和实验研究的热点。预计这些原子核的基态形状会随着相同的变形驱动轨道的占据而随着质量的增加而从球形演变为三轴、扁圆形、长形，然后再回到球形。此外，激发态能级可以具有与基态显著不同的结构。例如，在68Se和72Kr中，扁圆变形的基态带与长形变形的激发态带共存。该区域低洼态激发能的变化常用于分析远离双魔56Ni核的结构演变。然而，电磁跃迁率被认为提供了一个更敏感的集体和变形探针。当前提案的目标是启动一项研究计划，研究沿N=Z线的重核电磁跃迁率，旨在测量四极变形和三轴性，以及识别形状转变和形状共存的特征。在寿命大于1皮秒和小于1皮秒的情况下，选择的实验方法分别是反冲距离法（RDM）和多普勒频移衰减法（DSAM）。感兴趣的状态将在复合核反应之后填充；实验装置将包括TIGRESS阵列，TIGRESS集成柱塞（TIP）装置与CsI带电粒子探测器阵列一起工作，未来还将包括DESCANT中子探测器阵列。第一个实验将分别通过40Ca（36Ar,2alpha）和40Ca（40Ca,2alpha）反应解决68Se和72Kr中的形状共存问题。

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.