COMPLETE FUSION AND ITS LIMITATION

Abstract

First, a definition of complete fusion is given. Amongst hard collisions which pass through a composite system, a distinction is made between deep inelastic collisions where some fusion process occurs, quasi-fission where a complete damping is attained, complete fusion and compound nucleus formation. Complete fusion corresponds to interactions where both partners are joined together a time much longer than the collision time and make an intermediate which decays into the final products without particular remembrance of the composition of projectile and target. It might differ from compound nucleus formation as far as the full equilibrium before decay is not required. It is shown how there is a continuous evolution between smooth inelastic collisions and compound nucleus formation. An analysis is made in section 2 of the deduction of the interaction barrier for fusion (incomplete and complete) from cross section measurements in the cases of light and medium systems at low energies for which fission is a negligible process. An attempt is made to explain oscillations in the excitation functions for σCF in (12C + 16O). In section 3 the limitation to complete fusion due to high orbital angular moment α and the very useful concept of critical distance are explained (Galin et al., and Bass). The basic concept of the Alice code is discussed as well as the determination of lcr ħ from excitation functions. It is shown that the slope of decreasing branch of (HI, xn) excitation functions on the high energy side depends very strongly on some type of angular momentum limit. But it might not be the critical value for complete fusion, because high J population decays mainly by α particle emission. In section 4, the distinction between fission after complete fusion, preequilibrium fission and quasi-fission is made for heavy nuclei. The concept of rotating liquid drop fission barrier is discussed. The hypothesis of a limitation to complete fusion from low l-vawes is exposed, as well as the experimental results on excitation functions that has been obtained. It is shown that all other explanations, fail. As a conclusion, it is shown how complete fusion depends strongly on the energy dissipation and on the balance between conservative Coulomb forces and dissipative forces.