Reaction products arising from the interaction of ${}_{}{}^{11}{}_{}{}^{}$B${+\mathrm{}}^{12}$C and ${}_{}{}^{10}{}_{}{}^{}$B${+\mathrm{}}^{13}$C have been studied in the energy range 4<$E_{\mathrm{lab}\left(\mathrm{B}\right)<\mathrm{}9\mathrm{}}$ MeV/nucleon. From the total fusion cross sections for the two entrance channels, the critical angular momenta have been extracted and then compared as a function of compound nucleus excitation energy. Even though a limitation in the fusion cross section was observed, no common limitation was found in the critical angular momenta for these two systems up to at least a ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$ excitation energy of 60 MeV. Above this excitation energy, the experimental uncertainties make this point less clear. Up to an excitation energy of 60 MeV in ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$, a fusion limitation based on reaching a critical density of compound nucleus states like the yrast or ‘‘statistical’’ yrast line cannot be responsible for the fusion cross section limitations observed for these entrance channels. The present data suggest that competing entrance channel processes are responsible for the observed fusion cross section limitations.

• Received 9 October 1984

DOI:https://doi.org/10.1103/PhysRevC.31.867