Limitation to complete fusion during a collision between two complex nuclei

Experimental results on the limits observed for complete fusion between heavy nuclei are discussed. It is shown that there is no critical angular momentum independent of the bombarding energy and of the entrance channel. Excitation energy and total angular momentum of the compound system do not appear as good parameters for determining the complete fusion cross section. All the available results can be presented in terms of a critical distance of approach $R_{\mathrm{cr}}$. Such a distance is obtained when the kinetic energy of incoming nucleons equals the interaction potential and is related to the nuclear-matter density of both nuclei. For very heavy partners, a fusion barrier occurs, in addition to the interaction barrier.