Above-barrier enhancement of fusion in the 6He + 209Bi nuclear reaction

The fission cross sections for the 6He + 209Bi reaction as functions of the 6He-beam energy are measured. The experimental excitation functions for the reaction 209Bi(6He, 4n)211 At are also presented. The 6He secondary ion beam is obtained on the basis of the extracted-beam transport system of the U400-M accelerator (the Q4DQ spectrometer). A comparison of the experimental data obtained with available results for the 6He + 209Bi reaction shows that a pronounced enhancement of the fission cross sections in the above-barrier energy region is observed in the case of the reaction with the 6He beam. In order to fit the results of theoretical calculations to the experimental data, it is necessary to reduce the Coulomb barrier by 15% (20%). This corresponds to an increase of 1.5 (1.6) fm in the parameter r0 of the nuclear potential.