In order to study the physics responsible for a limitation in angular momentum in heavy-ion fusion reactions, fusion cross sections for the reactions ${}_{}{}^{28}{}_{}{}^{}$Si${+\mathrm{}}^{28}$Si, ${}_{}{}^{16}{}_{}{}^{}$O${+\mathrm{}}^{40}$Ca, ${}_{}{}^{32}{}_{}{}^{}$S${+\mathrm{}}^{30}$Si, and ${}_{}{}^{12}{}_{}{}^{}$C${+\mathrm{}}^{50}$Cr have been measured at several incident energies covering lower and higher energy regions by detecting the yields of the fusion-evaporation residues. The limiting angular momenta for fusion are extracted from the measured fusion cross sections and compared with calculations based upon several models. Through the systematic study of different entrance channels forming the same compound nucleus, a strong entrance channel effect has been observed for very asymmetric systems. Our conclusion is that the entrance channel is significant in limiting the fusion cross section in the higher energy region.

• Received 19 April 1985

DOI:https://doi.org/10.1103/PhysRevC.33.176