Entrance channel limitation of fusion

The results of investigations of the heavy ion reactions are presented. The fusion channel probabilities for symmetric systems (on the example of 90Zr+90Zr) and asymmetric systems (on the example 90Zr+124Sn) are considered. The entrance channel limitation of fusion at the Bass barrier is described by the fusion probability at this barrier. Probability p(Bb) strongly decreases with the fissility for fissilities above the threshold value 0.72. Isotopic trends are found. There are not explained by the extra-push model. The double magic 90Zr+90Zr system shows smaller barrier shifts and small fluctuations values compared to the heavier Zr isotopes. The largest barrier shifts and fluctuations are found for the system using 96Zr. With the number of neutrons outside the atomic N=50 shells the barrier shift and fluctuation increase. For the production of heavy elements using actinide targets the limitation in the entrance channel most urgently has to be measured reliably. Beams of 22Ne, 26Mg, 30Si together with target between 232Th and 244Pu are used. The system with an excitation energy of 15-20 MeV is cold enough to profit from the shell stabilization of the deformed superheavy system 266109. A γ-cascade finally cools the system to reach the ground state of 266109