Search for entrance channel effects in sub-barrier fusion reactions

At energies near and below the fusion barrier, theoretical models under-predict the mean angular momentum of the compound nucleus for a variety of heavy-ion fusion reactions. The systematics of the available data suggested a connection to the mass asymmetry of the entrance channel. In an effort to explore this observation, we have studied three systems (;The evaporation residue cross sections for all three systems were measured at Tandar Laboratories in Buenos Aires, Argentina. Cross sections were measured from 20% above the fusion barrier to about 5-10% below the barrier. The evaporation residues were collected on a catcher foil and counted offline. Using delayed x-ray activities we were able to determine the partial cross sections for each particle evaporation channel.;The fusion-fission cross sections for ;The mean angular momentum of the compound nucleus at each energy was determined at the University of Washington Nuclear Physics Lab. The ;Comparisons of our results with the theoretical models and between each system do not show any evidence of an effect related to the mass asymmetry of the entrance channel. Furthermore, our results suggest that the discrepancies previously reported may be due to systematic errors in the conversion of experimental...