Fusion and Emission ofH1andHe4in Reactions between Complex Nuclei at High Energies

We have measured cross sections for evaporation residues, fission, and direct and evaporative ${}_{}{}^1{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ in reactions of 222-340-MeV ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ with ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$, ${}_{}{}^{154}{}_{}{}^{}\mathrm{Sm}$, ${}_{}{}^{164}{}_{}{}^{}\mathrm{Dy}$, and ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$. Fusion cross sections are also presented for 77-167-MeV ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{182}{}_{}{}^{}\mathrm{W}$ and 187-MeV ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ + ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$. The $Z$ dependence of the evaporative H/He indicates a breakdown of phase-space models for fission-evaporation competition. The large cross sections observed for direct H/He emission force serious consideration of energy dissipation by H/He ejection during the initial impact.