FORMATION CROSS-SECTIONS OF NEUTRON-DEFICIENT POLONIUM ISOTOPES IN ASYMMETRIC AND SYMMETRICAL HEAVY-ION FUSION

Excitation functions are measured for the fusion reactions Al-27+Lu-175 and P-31+Tm-169 leading to the isotopes Po-192-198. A comparison to the data for the reactions Mo-100 + Mo-92-100 shows that characteristics bf the compound nucleus evaporation do not depend on the bombarding ion mass in the whole range of the entrance channel asymmetry up to the fully symmetrical systems. It is also shown that a satisfactory description of the experimental data is possible in the frame of the statistical deexcitation model only at an assumption involving, in comparison to theory predictions, a considerable reduction of macroscopic fission barriers for neutron-deficient isotopes of Bi.