Fusion cross sections for the ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ + ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ system have been measured by detecting the evaporation residues at five bombarding energies which correspond to high excitation energies in the compound nucleus: $E^{*}\left({}_{}{}^{27}{}_{}{}^{}\mathrm{Al}\right)=64-110\mathrm{}$ MeV. The ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ nucleus can be populated by four different heavy-ion entrance channels—${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ + ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$, and ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$—which are accessible to experimental measurements. Comparing the present data with those already existing for the above channels, it is found that for $E^{*}>60\mathrm{}$ MeV the curves $E^{*}$ vs $J_{\mathrm{cr}}$ for each system converge, which may be indicative of a limitation imposed by the compound nucleus. The data are discussed in terms of existing models for entrance channel and statistical yrast line limitations. The highest energy point also suggests the existence of a maximum absolute angular momentum limit of $\sim 28\hslash$.

NUCLEAR REACTIONS ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ + ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ $E\left({}_{}{}^{14}{}_{}{}^{}\mathrm{N}\right)=86.0, 103.8, 149.0, 161.3, \mathrm{and} 180.0$ MeV; measured $\frac{d^2\sigma }{d\Omega \mathrm{dE}}$ for reaction products from $Z=5\mathrm{} \mathrm{to} 12$. Extracted ${\sigma }_{\mathrm{fus}}$, ${\sigma }_D$, ${\sigma }_R$.

• Received 4 June 1982

DOI:https://doi.org/10.1103/PhysRevC.26.1490