Session T4: Bonner Prize Session

Tom W. Bonner Prize in Nuclear Physics Talk: Symmetries and Simple Patterns in Nuclei

Nuclei are complex many-body objects that display remarkably simple patterns and regularities, both for a given nucleus and across regions of nuclei. The juxtaposition of these two facets of nuclear structure is reflected in two general, and complementary, approaches to their description -- a microscopic (femtoscopic, of course) perspective in terms of the motions of the individual nucleons and their interactions, and a macroscopic view of the nucleus as a whole, in terms of its shapes, symmetries, and collective behavior. The first part of this talk will discuss the simple patterns nuclei exhibit and interpret them in terms of symmetries, such as those of the Interacting Boson Approximation (IBA) model, elementary collective modes, changes in shell structure, and quantum phase transitions in the equilibrium structure. It is also possible to approach structural evolution in nuclei with an extremely simple, more microscopic, perspective focusing on the competition of the most important residual interactions, pairing and the valence proton-neutron ($p-n)$ interaction. While this is not a substitute for a comprehensive theoretical treatment, which remains a challenge and goal of nuclear theory, such an analysis leads to simple approaches, such as the $N_{p}N_{n}$ scheme and the $P$-factor, that correlate large amounts of nuclear data, can guide estimates of unknown nuclei, and which are highly sensitive indicators of changes in shell structure and of nuclei that exhibit behavior deviating from normal tends. Finally, empirical means of extracting information on the critical valence $p-n$ interaction will be discussed and the systematic behavior of these interaction strengths will be linked to shell structure on the one hand, and the onset and development of collectivity on the other.   

Symmetries in nuclei: New methods and applications

When a symmetry is a ``good'' symmetry of the nuclear system, as in the dynamical symmetries of the shell model and interacting boson model, this symmetry can directly give the spectroscopic properties of the nucleus, without the need for involved calculations. However, even if a symmetry is strongly broken, it nonetheless provides a calculational tool, classifying the basis states used in a full computational treatment of the many-body problem and greatly simplifying the underlying computational machinery. The symmetry then serves as the foundation for a physically meaningful truncation scheme for the calculation. This talk will provide an introduction to new applications of symmetry approaches to the nuclear problem, including the required mathematical developments.   

Probing simple patterns in complex nuclei with transfer reactions

The first observation of the O(6) limit of the Interacting Boson Model provided an unexpected benchmark for nuclear structure. A shape intermediate between a spherical vibrator and deformed rotor was a new simple pattern that described the complex nucleus, 196Pt. Shortly thereafter simple patterns in odd-mass nuclei were recognized as the coupling of a fermion to O(6) structures of the core. In addition to selection rules for electromagnetic transitions, there were now selection rules for single-particle transfer. As the properties of nuclei further from stability are explored, identifying simple patterns in complex nuclei becomes even more important as benchmarks in extrapolations of nuclear models to even more exotic nuclei. Identifying such benchmarks requires a full spectrum of spectroscopic probes, including single-particle transfer reactions. The present talk will provide an overview of how transfer reactions have been used to identify simple patterns in complex nuclei, from proton transfer reactions near 196Pt to recent neutron transfer work near 132Sn, eight neutrons from stability.