Measurement of evaporation residue cross-sections of the reaction 30Si + 238U at subbarrier energies.

The reaction 30Si + 238U → 268Sg* was studied at beam energies close to the Coulomb barrier. At the above barrier energy of Ec.m. = 144.0 MeV (center-of-mass energy at half thickness of the target), we measured three decay chains of 263Sg produced by evaporation of five neutrons. The cross-section was (67-37+67) pb. At subbarrier energy of Ec.m. = 133.0 MeV we measured three spontaneously fissioning nuclei which we assigned to the isotope 264Sg. The half-life of (120-44+126) ms was determined. The production cross-section was (10-6+10) pb, which is about four orders magnitude larger than the calculation based on the one-dimensional barrier penetration model in the fusion process, showing fusion enhancement caused by the prolate deformation of 238U. At Ec.m. = 128.0 MeV an upper cross-section limit of 15 pb was measured. Compared to excitation functions measured for the lighter system 16O + 238U → 254Fm*, a reduction of the fusion probability was observed at low beam energies indicating increasing competition from quasifission processes. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]