The cross-sections for the formation of evaporation residues in 70Zn and 86Kr induced reactions with 150Nd and 130,136Xe isotopes were measured for excitation energies of the compound nuclei (216,220,222Th) varied from 7 MeV to 70 MeV, at the linear accelerator UNILAC of the nuclear facility GSI, Darmstadt (Germany). After de-excitation by evaporation (xn, pxn et αxn), the residual nuclei are separated from the primary beam and from parasitic reaction products by the velocity filter SHIP and are implanted into a silicon localisation detector. Their subsequently decay via alpha particles with characterised energies allows us to identify them and to deduce their production rate. Experimental fusion-evaporation excitation functions are compared with those leading to the same compound nuclei obtained with other projectile and target combinations and with those calculated with a code developed at GSI. This code allows us to evaluate the evolution of the fusion probability as a function of the incident energy for each system. The variation of cross-sections and of the fusion probability is studied as a function of the macroscopic and microscopic variables of the partners. For the synthesis of super-heavy elements, these results demonstrate quantitatively the interest in using partners of fusion with closed shell structures and rich in neutrons (the fusion cross-section increases by a factor of 9 for a complementary pair of neutrons). On the other hand, closed shell compound nuclei does not influence the fusion cross-section. It will be worth synthesising nuclei with Z greater than 110 with neutron rich projectiles coming from secondary beams, isotopes approaching the predicted stability valley.
