| Fusion reactions with radioactive neutron-rich projectiles have been the subject of much recent theoretical and experimental interest. Predictions of enhancement of the cross section due to the use of a neutron-rich projectile may have implications for synthesis of heavy nuclei. In this work, the fusion-fission excitation functions were measured for the 32,38S + 181Ta reactions. The radioactive 38S beam was produced by projectile fragmentation. In the 32S-induced reaction, an incomplete fusion component was observed at high energies, with average momentum transfer corresponding to escape of an alpha particle. Angular distribution data were used to estimate the quasifission component of the stable-beam reaction. The excitation functions were analyzed using classical and coupled-channels methods; the deduced interaction barriers were 130.7 +/- 0.3 MeV and 124.8 +/- 0.3 MeV for the 32S- and 38S-induced reactions, respectively. No evidence of any additional mechanism beyond a simple shift in the Coulomb barrier was observed. Taking into account the difference in reaction Q-values, the net lowering of the compound nucleus excitation energy at the barrier is about 12 MeV due to the use of the radioactive neutron-rich projectile; this could significantly affect survival probabilities of heavy nuclei. |
