Title: Probing Nuclear Collective Dynamics with Polarized Photons at Hlγs 

Abstract: Electromagnetic probes provide a clean and selective window into the microscopic structure of atomic nuclei. Real photons couple directly to nuclear charge and current distributions with minimal distortion from the interaction mechanism, making resonant photon scattering particularly well suited for high-resolution studies of electric and magnetic dipole excitations. In this seminar, I will present recent photon-scattering measurements performed with quasi-monochromatic, highly polarized beams at the High Intensity Gamma-ray Source (HIγS) at the Triangle Universities Nuclear Laboratory. 

These experiments map dipole-strength distributions from low excitation energies to the vicinity of the particle-emission threshold, where the interplay of single-particle configurations and collective dynamics produces fragmented and often complex excitation patterns. Polarization asymmetries and angular distributions are used to determine multipole character, while measured intensities and decay branches provide access to reduced transition probabilities, branching ratios, and photon-strength functions. 

Selected results will be compared with state-of-the-art microscopic calculations and complementary measurements using hadronic probes. These comparisons elucidate the structure and evolution of low-energy dipole collectivity, test modern nuclear models, and constrain electromagnetic response functions relevant to nuclear reaction theory, astrophysical reaction rates, and nucleosynthesis.

Bio: Akaa D. Ayangeakaa is an associate professor in the Department of Physics and Astronomy at the University of North Carolina at Chapel Hill and a faculty member at the Triangle Universities Nuclear Laboratory. He joined UNC in 2020 after serving as an assistant professor in the Department of Physics at the U.S.  Naval Academy in Annapolis, Maryland. Before his faculty appointments, he was a postdoctoral research fellow in the Physics Division at Argonne National Laboratory. He earned his Ph.D. in experimental nuclear physics from the University of Notre Dame, where he also completed an M.S. in experimental nuclear physics. He also holds an M.Sc. in radiation and environmental protection from the University of Surrey in the United Kingdom and a B.Sc. in physics from Benue State University.

Ayangeakaa is an experimental nuclear physicist whose research focuses on the structure and dynamics of atomic nuclei. His work investigates how the interactions of protons and neutrons give rise to collective nuclear phenomena, including shell evolution, shape coexistence, triaxial deformation, quadrupole collectivity, high-spin structure and electromagnetic response. His research group uses advanced experimental techniques such as gamma-ray spectroscopy, Coulomb excitation, nuclear resonance fluorescence and in-beam spectroscopy at major national user facilities, including TUNL, Argonne National Laboratory and the Facility for Rare Isotope Beams.

At UNC, Ayangeakaa teaches a range of undergraduate and graduate courses. His teaching portfolio includes introductory physics, experimental physics laboratory courses and classical mechanics. He is teaching PHYS 885, the introductory graduate seminar, which helps incoming graduate students develop the professional, research and academic skills needed for success in graduate school and beyond.

In addition to his teaching and research, Ayangeakaa serves as associate chair for graduate studies and director of graduate studies, where he helps oversee graduate education, student progress, admissions, mentoring and graduate-program development. He has also contributed to departmental committees related to graduate admissions, diversity, undergraduate affairs and student training.

Ayangeakaa is active in the broader nuclear physics community through national and international service. He has served on organizing and advisory committees, reviewed proposals for federal funding agencies, refereed manuscripts for leading nuclear physics journals and contributed to community-wide efforts aimed at strengthening nuclear science. Through his research, teaching, mentoring and service, he is committed to advancing the understanding of the atomic nucleus while training the next generation of scientists.