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 from abnormally long-lived states and various X- and γ-rays were observed, e.g. 7.8–8.6 MeV α-particles with γ-rays of a superdeformed band, 5.1–5.5 MeV α-particles with X- and γ-rays of W, Re and Pt, and 3.88 MeV particles (interpreted as protons) with 185.8 keV γ-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.