The role of the compound nucleus in complex fragment emission at low and intermediate energies

Abstract

The origin of complex fragments produced at low and intermediate energies is discussed and the leading theories as well as the experimental evidence are reviewed. Particular attention is focused on the compound nucleus formed in either complete or incomplete fusion as a possible source of complex fragments. Theoretical aspects of compound nucleus emission are reviewed in detail. The experimental demonstration of the existence of compound nucleus emission at extremely low energy is given and the process is followed by means of a series of reactions up to 50 MeV/u. These results allow one to conclude that, in the general class of reactions under investigation, complex fragments come either from statistical compound nucleus emission, or they are target and/or projectile-like fragments formed in quasi and deep inelastic reactions, or in incomplete fusion as spectators. The multifragmentation process is discussed in terms of novel theories like liquid-vapor equilibrium, nuclear shattering, nuclear disassembly, etc. as well as in terms of established physics like the process of comminution resulting from the sequential emission of many fragments from an extremely excited compound nucleus. The origin of fragments at higher energies is also briefly considered.