EVOLUTION OF PRECOLLECTIVE NUCLEI AND A TRIPARTITE CLASSIFICATION OF NUCLEAR-STRUCTURE

Precollective nuclei, that is, those with E(4(1)+)/E(2(1)+) < 2.0, are shown to evolve structurally in a very simple and universal way, in which E(4(1)+) is linear against E(2(1)+) with a slope of unity. A clue to this behavior is provided in terms of a seniority upsilon =0 pair addition mode. Combined with recent studies of vibrator and rotor nuclei, this ''seniority'' regime gives a new tripartite global characterization of the evolution of nuclear structure.