Theoretical Nuclear Structure Physics

Louisiana State University, Baton Rouge LA

Investigators

Abstract

0140300 Draayer The nuclear theory program at Louisiana State University (LSU) in Baton Rouge is focused on understanding the structure of atomic nuclei; specifically, we examine key ingredients of the strong interaction that binds nucleons (neutron and protons) in the nucleus. There is both a basic science and an applied aspect to what we do: On the basic science side we probe the "nuclear soup" - trying to understand how the strong interaction, which can be drilled down to a consideration of the structure of the nucleons themselves, manifests itself in the nuclear medium. This is important since we cannot claim we really understand an object unless we can tear it apart and put it back together again. We know, for example, that nuclear display certain characteristic features, such as independent particle behavior near closed shells and collective rotations - like that of a quantum top - away from closed shells. The drivers of these simple characteristics, which the composite system filters from the complex nucleon-nucleon interaction, remain elusive and hence a roadblock to a deeper understanding of the structure of atomic nuclei. On the complementary applied science side, one can gain a better appreciation for practical implications of what we do by asking a very general but important question: "Is it important to understand systems and related processes that are responsible for most of the energy stored in the universe?" If it is important to understand at a deeper level this "ultimate source of energy", then the study of nuclear physics, as well as the training of students who will shepherd future developments in this area, has real value to our nation and humankind. It is within this larger framework that we see and do our work. We are particularly interested in the structure of rare earth and actinide nuclei because in these nuclei that the collective modes are strongly enhanced through the involvement of a large fraction of the total number of constituent nucleons. Such studies require theoretical tools beyond those of the usual shell and collective models, which nonetheless by virtue of their successes provide guidance and limits on all new approaches. Our research exploits symmetry methods, from point groups to q-deformed and infinite-dimensional algebras, as well as non-linear dynamics. The proposed work, which will continue our ongoing program, is organized into three areas: 1) shell-model and related investigations; 2) group theory and algebraic methods; and 3) collective motion and nonlinear dynamics. Recent successes in each of these areas include, respectively: 1) the articulation of "twist" and "scissors + twist" modes as collective M1 transitions in strongly deformed nuclei; 2) an algebraic solution of the generalized pairing problem, inclusive of non-degenerate single-particle energies; and 3) the evolution of deformation in nuclei to solitons (dubbed rotons) on the surface of a liquid drop. The training of graduate students, most from abroad, has been and will continue to be an important complementary educational and out-reach feature of our program. To date, the PhD student profile in theoretical nuclear physics program at LSU is: 1 African- American (the first in physics to graduate from LSU), 1 Korean, 1 Pakistani, 4 Germans, 1 Indonesian, 1 Ukrainian, 1 Romanian, 4 Bulgarian, and 2 Armenian.