Entrance-channel effects in the population of superdeformed bands in Gd147,148

Discrete superdeformed bands in Gd147,148 have been populated with asymmetric and symmetric fusion-evaporation reactions. The yields of the superdeformed bands compared with the total yield of the channel exhibit a large increase for symmetric reactions. We suggest an explanation for this effect in terms of the competition between neutron emission and fission at the early stage of the deexcitation process of the composite system.