RUI: Exotic Shapes in Rare-Earth and Neutron-Rich A~100 Nuclei

人们观察到原子核以各种形状存在，包括球形、长方形(像橄榄球)、扁圆形(像门把手)，甚至八极(像梨)。此外，单个原子核可能有多种形状，这取决于它拥有多少激发能量和/或角动量。理论家根据他们对质子和中子之间的作用力的理解，预测出了比上述更奇特的形状。这项研究计划是基于为这些不寻常的形状寻找实验证据。几乎所有描述的形状都至少有一个对称轴。也就是说，存在一个质量分布完全对称的轴。几十年来，人们一直预测不对称的原子核，即缺乏对称轴，但直到最近，关于它们存在的令人信服的证据还很有限，其中一些原子核被发现表现出“摇摆”的行为。这个项目将寻找除迄今已发现的非常小的样本之外的其他例子。也许更奇怪的是最近关于原子核具有四面体形状的预测，也就是说，原子核具有非常圆形的金字塔结构。我们计划通过观察这种原子核衰变时发出的伽马射线的模式来寻找这种原子核；这可以为四面体形状的存在提供信号。美国海军学院的本科生和佛罗里达州立大学的研究生将带头分析这些数据集。这些项目将使这些学生接触到核科学领域，作为一种可能的职业选择。

The atomic nucleus has been observed to exist in a variety of shapes including spherical, prolate (like a rugby ball), oblate (like a door knob), and even octupole (like a pear). In addition, a single nucleus may have multiple shapes depending on how much excitation energy and/or angular momentum it possesses. Even more exotic shapes than those mentioned have been predicted by theorists based upon their understanding of the forces between the protons and neutrons. This program of research is based on finding experimental evidence for these unusual shapes. Almost all of the shapes described have at least one axis of symmetry. That is, an axis exists where the mass distribution is perfectly symmetric about it. Nuclei that are asymmetric, i.e. lacking a symmetry axis, have been predicted for decades, but compelling evidence of their existence has been limited until very recently, where a few nuclei were found to exhibit "wobbling" behavior. This project will search for other examples beyond the very small sample that have been found to date. Perhaps even more exotic is the recent prediction of nuclei possessing a tetrahedral shape, that is, having a very-rounded pyramid structure. We plan to look for such nuclei by observing the pattern of gamma rays emitted when such nuclei decay; these can provide the signature for the existence of tetrahedral shapes. Undergraduate students from the U.S. Naval Academy and graduate students from Florida State University will take the lead in analyzing these data sets. These projects will expose these students to the nuclear science field as a possible career choice.