REGULARITY AND CHAOS IN LOW–LYING 2⁺ STATES OF EVEN–EVEN NUCLEI

Abstract

Using all the available empirical information, we analyse the spacing distributions of low-lying 2 + levels in even-even nuclei by comparing them with a theoretical distribution characterized by a single parameter (the chaoticity parameter f ). We use the method of Bayesian inference. We show that the necessary unfolding procedure generally leads to an overestimate of f . We find that f varies strongly with the ratio R 4/2 of the excitation energies of the first 4 + and 2 + levels and assumes particularly small values in nuclei that have one of the dynamical symmetries of the Interacting Boson Model.