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.