Characterization of the β vibration and 0⁺₂ states in deformed nuclei

A summary of the experimental properties of the first excited 0⁺ states in deformed rare-earth nuclei is presented. By appealing to the original definition of a β vibration laid down in the Bohr-Mottelson picture, it is re-emphasized that most of the 0⁺₂ states are not β vibrations. A consideration of all available data, especially that from transfer reactions, and of microscopic calculations of 0⁺ states underscores the need to consider the role of pairing in the description, and labelling, of these states.