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 a center-of-mass energy of E _c.m. = 144.0MeV for reactions at half thickness of the target we measured three decay chains of ²⁶³Sg produced by evaporation of five neutrons. The cross-section was ( 67⁺⁶⁷ _-37) pb. At E _c.m. = 133.0MeV we measured three spontaneously fissioning nuclei which we assigned to the isotope ²⁶⁴Sg. The production cross-section was ( 10⁺¹⁰ _-6) pb and a half-life of ( 120⁺¹²⁶ _-44) ms was determined. This half-life is a factor of twenty shorter than theoretical predictions. At E _c.m. = 128.0MeV an upper cross-section limit of 15pb was measured. The cross-section data reveal a strong influence of the orientation of the deformed target nucleus on the production yield. 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.