Incomplete fusion in theZn40reaction: Trends and limits

The heavy fragments emitted in the ${}_{}{}^{40}{}_{}{}^{}$Ar${+\mathrm{}}^{68}$Zn reaction have been studied at ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ energies of 14.6, 19.6, 27.6, and 35 MeV/nucleon. Fusion-evaporation and fusion-fission components resulting from complete and incomplete fusion were observed, and cross sections have been measured for both components at the four energies. The velocity distributions of the evaporation residues have been analyzed and the linear momentum transferred to the compound system deduced. Compared to other results, the momentum transfer appears to depend on the asymmetry of the system and on the projectile mass. The mass, excitation energy, and temperature of the compound nuclei formed have been determined. Fusion disappears slightly above 35 MeV/nucleon, which corresponds to a compound nucleus excitation energy of 500 MeV (5.9 MeV/nucleon) and to a temperature of 6.8 MeV. The results are discussed in terms of various theoretical models.