Search for entrance channel effects in the decay of the [sup 164]Yb compound nucleus at [ital E][sup *][approx]54 MeV

The existence of entrance channel effects in the decay of [sup 164]Yb[sup *], formed at [ital E][sup *][approx]54 MeV in the reactions [sup 16]O+[sup 148]Sm and [sup 64]Ni+[sup 100]Mo is investigated. Evaporation residue cross sections, entry state [gamma]-ray fold distributions as well as energy and angular distributions of exit channel selected charged particles were obtained for each reaction, using 4[pi] detection systems for both particles and [gamma] rays. In the [sup 64]Ni-induced reaction, the center-of-mass [alpha]-particle angular distributions were found to be symmetric around 90[degree] indicating emission from a fully equilibrated compound nucleus. However, the corresponding angular distributions in the [sup 16]O-induced reaction show a forward component which exclusively affects the population of the [alpha][ital xn] residue channels. The [gamma]-ray fold distributions for the [alpha][ital xn] and [ital 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 [sup 16]O with [sup 148]Sm and the mapping of the compound nucleus spin distributions, obtained from realistic fusion models, to the evaporation residue [gamma]-ray fold distributions. It is concluded that the initial population of the compound nucleus is the only reasonmore » for the observed differences in the decay of [sup 164]Yb[sup *] populated in these reactions.« less