Discovery of Long-Lived Shape Isomeric States which Decay by Strongly Retarded High-Energy Particle Radioactivity

The reaction 28Si + 181Ta has been studied at E(Lab) = 125 and 135 MeV. Coincidences between high energy particles and various X- and gamma-rays from abnormally long-lived states were observed. e.g. 7.8 - 8.6 MeV alpha-particles 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 (interpreted as protons) with 185.8 keV gamma-rays. The data are interpreted in terms of the production of long-lived (t(1/2) of several months) high spin isomeric states in the second well of the potential in the parent nuclei, which decay to the normal states in the daughters, and in the third well of the potential, which decay to the second well.