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

当仔细研究原子核的性质时，它可以表现出许多不同的特征。单个原子核已经量子化了能级。根据原子核是变形的还是球形的，这些能级的模式以及在能级之间发射的对应于tto衰变的伽马辐射是不同的。一些原子核在低能量和角动量(旋转)下具有形变的长椭圆形的性质，而在高角动量下的单粒子性质更符合球形的性质。当核心外的所有粒子都与旋转轴对齐时，通常会出现这些单粒子状态。所有粒子排列在一起的状态通常称为能带终止态。在很高的自旋下，154Er核及其邻近核既有单粒子(带终止)结构，又有集体结构。154Er核有两个已知的高自旋能带结构。与理论的比较表明，这对应于四极大变形的构造，其中一个是拉长超形变(SD)，另一个是三轴强变形(TSD)。这一结论是基于测量的伽马射线能量和推导的转动惯量得出的。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更好的方法。我们最近对157158Er(2009年2月)TSD带的寿命测量已经产生了令人惊讶的大的四极矩，这可能需要理论的完善。154Er中两种不同形状的共存将为这个问题提供更多的线索，并将作为对高自旋时奇异核形状的校准。这项实验将使用美国阿贡国家实验室的GAMMASPHERE阵列进行。数据收集时间为7天。这些数据随后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学生论文的一部分。

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.