Probing Nuclear Structure with Fast Neutrons

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Atomic nuclei are composed of protons and neutrons and exhibit a variety of shapes. Some nuclei are spherical, while others have non-spherical shapes (similar to an onion, a zucchini, or a pear); the shape of the nucleus is unique for each isotope of each element. Because we cannot take an ordinary photograph of the nucleus to investigate its shape and structure, other methods must be employed. Through reactions at the University of Kentucky particle accelerator, neutrons are produced and then scattered from the nucleus. In the process, the nucleus gains and subsequently releases energy that can be detected. This information is used to deduce the shape of the nucleus and to gain an understanding of how the neutrons and protons in the nucleus contribute to its properties. Graduates of this research program receive hands-on experience with particle accelerator operation, nuclear science instrumentation, radiation detection, and data acquisition systems, and emerge as well-trained nuclear scientists who are capable of important contributions to our national needs. The broad-based research program at the University of Kentucky Accelerator Laboratory includes studies in several forefront areas: nuclear structure relevant to neutrinoless double-beta decay; nuclei undergoing shape transitions; deformed structures and shape coexistence; nuclear structure contributions in support of searches for fundamental symmetries. In this research, the inelastic scattering of fast neutrons is used to examine low-energy collective nuclear excitations and to obtain information, e.g., level lifetimes and transition multipole mixing ratios for non-yrast states, which is inaccessible with other reactions. Detailed investigations of stable nuclei complement advances in nuclear structure achieved by studying nuclei at extreme conditions of temperature and angular momentum or in regions far from stability. Experimental innovations in the laboratory, e.g., the development of capabilities for measuring lifetimes in heavy nuclei, have played a key role in this research. These advances, coupled with the unique capabilities of this laboratory for the production of high-quality, time-bunched monoenergetic neutrons, probe important questions and make meaningful contributions to our knowledge of nuclear structure.