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182 Nuclear Physics Highlight: Future Leaders in Nuclear Science and Its Applications: Stewardship Science Graduate Fellows To address compelling concerns in national and homeland security requires highly trained, talented individuals in a variety of disciplines, including nuclear science. The Department of Energy’s National Nuclear Security Administration (NNSA) has identified the need to develop a highly talented workforce of U.S. citizens to meet the long-term requirements of national security and the stewardship mission of NNSA. To meet this need, the NNSA established the Stewardship Science Graduate Fellowship program in the areas of high-energy-density physics, materials under extreme conditions, and low-energy nuclear science. In addition to receiving stipends and tuition remission, all fellows are required to spend at least 3 months in residence at one of the NNSA laboratories for a practicum. Of the 23 fellows in the first 5 years of the pro- gram, 8 are doing research in nuclear science. The stories of four of these fellows are told here. To find a robust energy source with minimal emission of greenhouse gases will require a renewed commitment to nuclear energy and developing the next generation of nuclear reactors. Preparing for this next generation of nuclear reactors requires an understanding of the probabil- ity that actinides other than uranium-235 or plutonium-239 will fission. As a part of his Ph.D. dissertation work, Paul Ellison, a fellow from the University of California at Berkeley, is devel- oping techniques to measure the fission probability of the rare isotope americium-240, which has a half-life of only 51 hours (Figure FEL 1). He will be creating this isotope with a nuclear FIGURE FEL 1 Graduate student Paul Ellison with the Berkeley Gas-Filled Separator, used for studying the chemistry and physics of the heaviest elements. SOURCE: Image courtesy of PT Lake.
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S o c i e t a l A pp l i c a t i o n s and Benefits 183 reaction in which plutonium-242 is bombarded with protons at the energy that maximizes the emission of three neutrons to make americium-240. Once he has mastered the techniques to produce the tiny amounts (<100 ng) of americium-240 required to measure fission probabilities, experiments will be performed at the LANL Neutron Science Center, where he has already spent several months as part of his practicum. Paul also performs fundamental low-energy nuclear physics research on the heaviest elements, such as the yet unnamed element-114. The nucleus is a complex quantum system made of neutrons and protons. One goal of nuclear structure research is to establish a unified framework for understanding the properties of atomic nuclei and, potentially, for extrapolating to the limits of nuclear existence. Fellow Angelo Signoracci from MSU is working on such a unified framework (Figure FEL 2). He will be developing a hybrid method that builds on decades of experience with shell model calcu- lations, which provide detailed predictions of nuclear structure with many input parameters, and the energy density functional approach, which could predict the entire nuclear landscape with one parameterization. By spending his practicum at LLNL, he was able to interact with the laboratory’s scientists, who are leading efforts that exploit its petascale computing facilities. FIGURE FEL 2 Graduate student Angelo Signoracci develops computer models of the structure of atomic nuclei. SOURCE: Image courtesy of K. Kingery, Communications manager at MSU’s National Superconducting Cyclotron Laboratory. continued
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184 Nuclear Physics The ability to detect low levels of radiation is important for many applications and critical for detecting weakly interacting particles such as neutrinos and dark matter. Nicole Fields, a fellow from the University of Chicago, is developing and characterizing P-type point contact (PPC) germanium detectors and associated electronics (Figure FEL 3). These detectors will be the primary design component of the Majorana experiment that will search for neutrinoless double-beta decay and light-mass dark matter candidates. She also works closely with industry in improving these detectors. Upon completing 2 years of graduate studies, Nicole looks for- ward to doing her practicum. The detection of neutrons and understanding reactions induced by neutrons and protons are important for basic nuclear structure and astrophysics, as well as for applications in home- FIGURE FEL 3 Graduate student Nicole Fields is developing new systems to detect weakly interacting particles. SOURCE: Image courtesy of Lloyd DeGrane, University of Chicago.
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S o c i e t a l A pp l i c a t i o n s and Benefits 185 FIGURE FEL 4 Patrick O’Malley uses the ORNL accelerator and the ORRUBA array of position- sensitive silicon strip detectors to study nuclear reactions that help us understand how the elements are synthesized in stars. SOURCE: Patrick O’Malley. land security. The research of fellow Patrick O’Malley from Rutgers University is focused on nuclear reaction studies and in particular on the question of how the stable isotope fluorine-19 is synthesized in stars when nitrogen-15 interacts with alpha particles (Figure FEL 4). Patrick measured the reaction in which nitrogen-15 interacts with deuterium, emitting a proton and thereby transferring a neutron to form nitrogen-16. He hopes to understand the destruction of nitrogen-15 from interactions with neutrons in stars. Much of his research involves the charged- particle detectors of the ORNL-Rutgers University Barrel Array (ORRUBA). He is also part of the team developing the Versatile Array of Neutron Detectors at Low Energy. Patrick spent a summer at LLNL helping to develop the neutron time projection chamber, which can be applied to locate sources of special nuclear materials that emit neutrons.