STRUCTURAL-CHANGES IN HIGH-SPIN NUCLEI

The interplay of various degrees of freedom and their influence on the behaviour of nuclei formed as fused compounds in heavy-ion reactions is investigated. A statistical theory which incorporates deformation, collective and noncollective rotational degrees of freedom and shell e ffects is developed to study highly excited fused compounds which deex cite by particle emission and yrastlike cascades. We find that the nuc leonic separation energies, which are functions of spin and temperatur e, decrease rather sharply for particular angular momentum states of t he nuclei due to shape transitions. We predict an enhancement of nucle onic emission at these spins, and evidence for this is already present in the experiment of Henss et al. Results for heavy systems like Er, Yb and Hg which emit neutrons while rotating fast, and for light nucle i like Si-28, etc. which have greater probability for emitting protons and light charged particles, are presented.