Chaotic properties of the interacting-boson model: A discovery of a new regular region

The chaotic properties of the interacting-boson model of nuclei are studied both classically and quantum mechanically. Classical phase diagrams are constructed in the general parameter space of the Hamiltonian known as Casten’s triangle. They lead to a discovery of a nearly regular region which is probably related to an unknown approximate symmetry. Analysis of the quantum fluctuations of the spectrum and of the electromagnetic B(E2) intensities confirms the classical results. The phase diagrams may be useful in identifying ‘‘chaotic’’ nuclei within the nuclear periodic table.