Quasifission and difference in formation of evaporation residuesin the 160 + 184W and 19F + 181Ta reactions

摘要

The role of the entrance channel has been studied to ascertain a cause of the observed difference betweenthe evaporation residue cross sections normalized to the fusion cross sections in the ~(16)O+184~(19)F + ~(181)Taand W reactions at high excitation energies. The theoretical analysis performed in the framework ofthe dinuclear system and advanced statistical models showed that the more intense yield of evaporationresidues in the ~(16)O+ ~(184)Wreaction in comparison with that the 19)F+ 181)Tareaction was explainedby the large capture and fusion cross sections in the former reaction, which is in agreement with theexperimental data. The observed decrease in the evaporation residue cross section normalized to thefusion cross section in the ~(19)F+ ~(181)Tareaction, in comparison with one the 16)O + ~(184)W reactionat large excitation energies, is caused by the unintentional inclusion of the quasifission and fast fissioncontributions in the fissionlike fragment yields that were used in reconstructing the experimental fusioncross section in the normalizing procedure. The range of the angular momentum distribution for bothsystems was similar, but the partial cross sections are different, showing the presence of a difference inthe hindrance to complete fusion in both reactions.