DSAM Lifetimes of the SD and TSD bands in 154Er at ultra high spin

当详细研究原子核的性质时，它们可以显示出许多不同的特征。单个原子核具有量子化的能级。这些能级和对应于能级之间衰变的伽马辐射的模式是不同的，这取决于原子核是变形的还是球形的。一些原子核在低能量和角动量（旋转）下具有变形的长扁形形状的性质，并且在高角动量下具有与球形形状更一致的单粒子性质。这些单粒子状态通常出现在核心外的所有粒子都与旋转轴对齐时。所有粒子都对齐的状态通常被称为能带终止态。原子核154 Er及其邻居在非常高的自旋下具有单粒子（带终止）和集体结构。原子核154 Er有两个已知的高自旋能带结构。与理论的比较表明，这些对应的结构与大的四极形变，一个是扁长超变形（SD）和其他三轴强变形（TSD）。这一结论是基于测量的伽马射线能量和推导的惯性矩。用DSAM寿命测量来确定跃迁强度是探测高自旋核形变的一种好得多的方法。我们最近对157，158 Er的TSD带的寿命测量（2009年2月）产生了令人惊讶的大四极矩，这可能需要理论来完善。154 Er中两种不同形状的共存将为这个问题提供更多的线索，并将作为高自旋下奇异核形状的校准。该实验将在美国阿贡国家实验室使用伽马球阵列进行。数据将收集7天。然后，这些数据将在利物浦进行分析，以实现物理目标。这些数据将成为研究生论文的一部分。

Nuclei can display a number of different features when their properties are studied in detail. Individual nuclei have quantised energy levels. The pattern of these levels and the gamma radiation emitted corresponding tto decays between the levels is different depending on whether the nuclei are deformed or spherical. Some nuclei have the properties of deformed prolate shapes at low energies and angular momentum (rotation) and single particle properties more consistent with a spherical shape at high angular momentum. These single particle states often arise when all the particles outside a core are aligned with the rotation axis. The states where all the particles are aligned are often called band termination states. The nucleus 154Er and its neighbours have both single particle (band termination) and collective structures at very high spin. The nucleus 154Er has two known high-spin band structures. Comparison with theory suggests that these correspond to structures with large quadrupole deformation, with one being prolate superdeformed (SD) and the other triaxial strongly deformed (TSD). This conclusion is based on the measured gamma ray energies and deduced moments of inertia. DSAM lifetime measurements to determining transition strengths are a much better way to probe nuclear deformation at high spin. Our recent lifetime measurements of TSD bands in 157,158Er (Feb 2009) has yielded surprisingly large quadrupole moments which may require theory to be refined. The coexistence of two different shapes in 154Er will shed more light on this problem and will act as a calibration for exotic nuclear shapes at high spin. The experiment will be carried out using the GAMMASPHERE array at Argonne National Laboratory in the USA. Data will be collected for 7 days. The data will then be analysed in Liverpool in order to achieve the physics aims. The data will form part of the thesis of a resarch student.