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

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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.