Seminarium Fizyki Jądra Atomowego

Atomic nuclei are fascinating quantum objects which, nonetheless, we aim to understanding classically, for instance assigning them well-defined shapes. Indeed, experimental data on electromagnetic moments and transitions allows one to identify deformed structures in basically every nucleus across the nuclear chart. Moreover, in many nuclei one can assign distinct shapes to different nuclear states that appear at low energies, a phenomenon known as shape coexistence.

In this seminar, I will present a theoretical study on nuclear shape coexistence using the nuclear shell model. I will focus on two systems where multiple shapes have been either established experimentally or predicted theoretically. First, 28Si, which even though in the original naive shell-model proposed 75 years ago would correspond to a spherical nucleus because of the 0d5/2 closure, has a deformed ground state with an oblate shape. In addition, another deformed low-lying rotational bandhead appears at ~7 MeV excitation energy, in this case associated with a prolate shape. Furthermore, some theoretical calculations predict the appearance of superdeformed prolate states at low excitation energies about ~13 MeV. Second, I will deal with the doubly-magic nucleus 40Ca, which exhibits two very well-defined rotational bands, a normal-deformed prolate band with bandhead at ~3 MeV, and a superdeformed one at ~5 MeV.

In order to do so, I will discuss different theoretical tools. The fundamentals for deformation within the shell model lie on Elliott's SU(3) model, which provides a general framework to understand the possible deformed nuclear shapes at play in the relevant configuration space. In addition, calculated transition energies, quadrupole moments and B(E2) values are key when comparing to experimental data. Finally, the so-called deformation invariants provide reference-frame-independent values for the nuclear deformation in the beta-gamma plane. I will present novel results on how to determine these invariants for any nuclear state.