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.