Threshold behaviour in the fusion of massive systems

Beams of 124Sn and 86Kr from the UNILAC heavy-ion accelerator were used together with isotopically enriched targets of 92Zr, 94Zr, 96Zr, and 123Sb. The evaporation residues were separated from the primary beam by the velocity filter SHIP, and behind SHIP they were implanted into a surface-barrier detector. Here they were individually identified by their subsequent ~ decay. The experimental method is described in ref. [I]. As an example of the experimental results, the neutron-evaporation-residue cross sections for the reaction 124Sn + 96Zr are shown in fig. ic. In this case, the transmission of SHIP was calculated to range between 40~ and 56~.