Nuclear shapes and shape coexistence: from the early start to our present understanding

Kris Heyde (Department of Physics and Astronomy, University Gent, Belgium)

Starting from a number of early experiments, first in atomic physics, it was realized that nuclei can be realized with non-spherical intrinsic shapes.  These data early on showed a conflicting situation between on one side the nuclear shell model and an approach starting from deformed nuclear shapes when trying to explain these observables.

From a theoretical side, early work showed the possibility to find a way to understand both facets, using concepts  starting from underlying symmetries of the spherical nuclear shell model.

I will concentrate on the early observation of highly correlated excited states as unexpected low-lying nuclear excited 0⁺ states and associate collective bands.  I address the early status for light nuclei and the way these results highlighted the presence of unexpected effects of nuclear deformation near closed shells.

Besides discussing shape coexistence and the key ingredients in order for shape coexistence to be realized as low-lying excited states, as well as the logical consequences such as the presence of regions of inversion of spherical and deformed modes of excitation. I will discuss the equivalence of theoretical approaches starting from the nuclear shell-model, the exploration of the nuclear mean-field structure as well as indicate recent attempts to merge the best of both approaches. I also refer to the importance and the role played by symmetry concepts to describe nuclear properties such as shape coexistence.

I will end with the observation that even though nuclear shape is not a genuine observable, it is still possible using nuclear sum rules, both starting from Coulomb excitation data and, for any given nuclear model, given the wave functions for every excited state, calculate these higher-order sum rules and characterize these states with deformation parameters describing nuclear quadrupole deformation.

Practical information:

11h00 GANIL seminar room (105)
Coffee will be served 15mn before