Discovery of long-lived shape isomeric states which decay by strongly retarded high-energy particle radioactivity

The reaction Si-28 + Ta-181 has been studied at E-Lab = 125 and 135 MeV. Co incidences between high energy particles from abnormally long-lived states and various X- and gamma- rays were observed, e.g. 7.8-8.6 MeV alpha -parti cles with gamma -rays of a superdeformed band, 5.1-5.5 MeV alpha -particles with X- and gamma -rays of W, Re and Pt, and 3.88 MeV particles (interpret ed as protons) with 185.8 keV gamma -rays. The data are interpreted in term s of the production of long-lived (4/2 of several months) high spin isomeri c states in the second well of the potential in the parent nuclei, which de cay to the normal states in the daughters, and in the third well of the pot ential, which decay to the second well.