Search for entrance channel effects in the decay of the Yb164 compound nucleus at E*54 MeV

The existence of entrance channel effects in the decay of Yb*164, formed at E*54 MeV in the reactions O16+148Sm and Ni64+100Mo is investigated. Evaporation residue cross sections, entry state -ray fold distributions as well as energy and angular distributions of exit channel selected charged particles were obtained for each reaction, using 4 detection systems for both particles and rays. In the induced64 reaction, the center-of-mass -particle angular distributions were found to be symmetric around 90°indicating emission from a fully equilibrated compound nucleus. However, the corresponding angular distributions in the induced16 reaction show a forward component which exclusively affects the population of the xn residue channels. The -ray fold distributions for the xn and xn channels show differences depending on the entrance channel as reported previously for similar systems. These differences can be understood in terms of contributions from the equilibrium decay of incompletely fused O16 with Sm148 and the mapping of the compound nucleus spin distributions, obtained from realistic fusion models, to the evaporation residue -ray fold distributions. It is concluded that the initial population of the compound nucleus is the only reason for the observed differences in the decay of Yb*164 populated in these reactions.