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

RUI：稀土和富中子 A~100 原子核中的奇异形状

• 批准号: 0854815
• 负责人: Daryl Hartley
• 金额: $ 3.56万
• 依托单位: United States Naval Academy
• 依托单位国家: 美国
• 项目类别: Interagency Agreement
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-08-01 至 2013-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0854815&HistoricalAwards=false
• 关键词: RUI; Exotic; Shapes; Rare; Earth

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.

原子核被观察到以各种形状存在，包括球形、长形（像橄榄球）、扁圆形（像门把手），甚至八极形（像梨）。此外，单个原子核可以有多种形状，这取决于它拥有多少激发能和/或角动量。理论学家根据他们对质子和中子之间的力的理解，甚至预测了比上面提到的更奇特的形状。这个研究项目是基于寻找这些不寻常形状的实验证据。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。不对称的原子核，即缺乏对称轴，已经被预测了几十年，但直到最近才有令人信服的证据证明它们的存在，在那里发现了一些原子核表现出“摇摆”的行为。该项目将寻找迄今为止发现的非常小的样本之外的其他例子。也许更奇特的是最近对原子核具有四面体形状的预测，也就是说，具有非常圆的金字塔结构。我们计划通过观察这些原子核衰变时发出的伽马射线的模式来寻找这些原子核；这些可以提供四面体形状存在的标志。美国海军学院的本科生和佛罗里达州立大学的研究生将率先分析这些数据集。这些项目将使这些学生接触核科学领域，作为一种可能的职业选择。