Mechanism of the Spontaneous and Induced Two-Body Fragmentation of Heavy Nuclei

Abstract

The study of nuclear binary decay is one of the main methods in nuclear physics to investigate the large-scale nuclear collective motion, the role of the shell structure and cluster effects. The fission and the α—decay are two well-known extreme modes of binary decay of heavy nuclei. The mass distribution of the light fission fragment is cut off near A f ≤ 80. Then there is the wide unexplored region of the intermediate fragment masses 4 ≤ A f ≤ 80. As the α—decay is connected with the role of the 4He shell structure, and the fission process is influenced by the strong stability of clusters near 132Sn, we can expect that the binary decays in the intermediate fragment mass region are governed by the shells N,Z = 8, 20, 28, 50, 82 and 126. The gap between the two extreme limits began to fill in the 1970s when the intensive investigations of the fragmentation mechanism in in reactions with high-energy beams was started, see for example [1,2]. The discovery of the spontaneous emission of 14C by 223Ra [3–5] showed the shortcomings in the theory of two-body fragmentation phenomena. The known features of this phenomenon give us the possibility to treat it as a special kind of decay from ground and excited states which is often named “cluster radioactivity”. In our early work [6] we proposed the name “f-decay” to emphazise the similarity of this process both for the ground and the excited states.