Compound-Nucleus Decay along the Mass-Asymmetry Coordinate and the Role of the Businaro-Gallone Point

Fragments with atomic numbers covering the entire range of the mass-asymmetry coordinate ($Z=1\mathrm{}$ to $Z=\frac{Z_{\mathrm{CN}}}{2}$) were observed from the decay of compound nuclei (CN) produced in reactions of 7.4- and 8.4-MeV/nucleon ${}_{}{}^{74}{}_{}{}^{}\mathrm{Ge}$, ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$, and ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ with ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$. The evolution of the charge distribution with increasing mass of the compound nucleus ($A=83\mathrm{} \mathrm{to} 151$) reflects the topological change in the potential-energy surface associated with crossing the Businaro-Gallone point.