Role of mass asymmetry in fusion of super-heavy nuclei

By using well tested standard statistical model for calculating survival probabilities of super-heavy compound nuclei, P_surv, and reliably predicted capture cross sections σ_cap, "empirical" values of the fusion hindrance P_fus = σ_syn/(σ_cap · P_surv) have been determined from the formation cross sections σ_syn for production of super-heavy nuclei of 102 ≤ Z ≤ 113 measured at GSI Darmstadt and RIKEN. So determined fusion hindrance can be well reproduced with a simple model based on the Smoluchowski diffusion equation applied to describe thermal shape fluctuations of the fusing system. An applicability of this model for a wider class of fusing systems could be verified on data from an interesting experiment on the synthesis of isotopes of Hs (Z = 108) in the ¹³⁶Xe + ¹³⁶Xe reaction, scheduled to be carried out in Dubna this year. Synthesis cross sections for ^269-271Hs isotopes, strongly reduced by the fusion hindrance effect in this symmetric fusion reaction, are predicted. (author)