A new analysis of yrast energies in collective medium and heavy even-even nuclei shows two startling results. First, although these nuclei exhibit widely varying structure [the ratio E($4_1^{+}$)/E($2_1^{+}$) ranges from ∼2.0 to ∼3.33], they show a universal behavior of an anharmonic vibrator with nearly constant anharmonicity in which the multiphonon interactions are independent of the internal structure of the vibration. Second, the transition from anharmonic vibrator to rotor can be described by critical phase transitional behavior. These results suggest a reexamination of very basic ideas of structural evolution in finite-body nuclear systems.

• Received 9 April 1993

DOI:https://doi.org/10.1103/PhysRevLett.71.227