2024/12/18(Wed) 15:00 -16:00 七樓研討室 7F, P7A Seminar Room
Title
Unwelcome intruders: Getting a nucleus to come out of its shell (in ab initio calculations)
Speaker
Prof. Mark A. Caprio (University of Notre Dame)Abstract
Intruder states, involving shell model configurations in which nucleons are excited out of the valence shell, feature prominently in the excitation spectra of nuclei across the nuclear chart. In comparison to "normal" states, for which the structure is well described by valence space configurations, "intruder" states have access to a much larger configuration space, allowing them to develop highly collective structure and greater deformation. Their consequently larger correlation energy permits them to "intrude" into the low-lying spectrum. When weakly deformed normal states and highly deformed intruder states lie close to each other in energy ("shape coexistence"), the conditions are ripe for mixing of these states ("shape mixing"), and thus nuclear states which exist in a superposition of two distinct deformations.
Intruder states are notoriously challenging to describe in ab initio calculations, appearing too high in the excitation spectrum, if at all. However, with suitably soft interactions and sufficiently large-scale calculations, it becomes possible to reproduce intruders at realistic energies in the low-lying spectrum. In this seminar, we will first review the goals, methods, and (notably) challenges of ab initio nuclear structure calculations, with an emphasis on the emergence of deformation and collective rotational structure. We will then explore low-lying intruder structure in nuclei at the neutron N=8 shell closure, through ab initio calculations. We will see that mixing between normal and intruder configurations can roughly be described as a simple two-state mixing, in which we can extract a consistent mixing matrix element, even though this mixing is entirely an emergent phenomenon.
Language
演講語言 (Language): in English