Differential cross sections for evaporation residue formation following complete fusion of ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$ and ${}_{}{}^{74}{}_{}{}^{}\mathrm{Ge}$ with 171 to 215 MeV ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ and ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$ ions were measured with high precision using a velocity selector together with a counter telescope. The resulting excitation functions for complete fusion ranged in magnitude from 10 μb to 300 mb. The excitation functions exhibited a strong response, at sub-barrier energies, to changes in the underlying nuclear structure. We interpreted these variations as evidence that the fusion proceeds through dynamic single-particle/softness-related processes. A phenomenological analysis was performed. In the analysis, we employed the Wentzel-Kramers-Brillouin method, constructed a simple interaction potential and introduced a radially-dependent effective mass. The use of the variable effective mass led to a meaningful description of our above-barrier data and to improvements towards describing our sub-barrier data.

NUCLEAR REACTIONS Complete fusion, ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ + ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$, ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ + ${}_{}{}^{74}{}_{}{}^{}\mathrm{Ge}$, ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$ + ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$, ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$ + ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$, ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$ + ${}_{}{}^{74}{}_{}{}^{}\mathrm{Ge}$, $E=171\mathrm{} \mathrm{to}215\mathrm{}$ MeV (lab), measured $\sigma (E,\theta )$ for evaporation residues; observed dynamic, single-particle/softness effects; performed barrier-penetration analysis.

• Received 27 July 1981

DOI:https://doi.org/10.1103/PhysRevC.25.837