Study of evaporation residues produced in reactions of207,208Pb with50Ti
Evaporation residues produced in heavy-ion fusion-reactions of50Ti and207Pb,208pb have been investigated. They were separated from the projectile beam by the velocity filter SHIP and identified after implantation into position-sensitive surface-barrier detectors, where their α decay or their decay by spontaneous fission was measured. The production of weakly excited compound nuclei in reactions of projectiles and targets close to the doubly magic48Ca and208Pb was confirmed by the observation of the 1n deexcitation channel in the reaction50Ti +208Pb.The spontaneous fission activities of255104 and256104 could be confirmed; improved halflives are (1.4−0.2+0.2)s and (7.4−0.7+0.9)ms. Furthermoreα-decay of255104 (ba=0.48 ±0.07) and an indication for a smallα-branch (ba= 0.022−0.018+0.073) of256104 was found.A total kinetic energy of (207±13)MeV released in spontaneous fission of256104 was measured.A statistical model analysis of the evaporation-residue cross sections is shown to give evidence for a dynamic hindrance to complete fusion in the system50Ti +208Pb, as well as for non-equilibrium components in the deexcitation mechanism.