A large set of experimental observables for the 232 Th , 235 U (α, xnf ) reactions has been analyzed within the dynamic-statistical approach with allowance for the nuclear dissipation phenomenon, the double humped structure of fission barrier, and also the temperature damping of shell effects. The energy dependences of the lifetime effect (experimentally measured by the crystal blocking technique) along the corresponding data on the fission fragment angular anisotropy and also fission probabilities of U and Pu isotopes produced in the reactions were chosen for the analysis. Reliable information on the nuclear viscosity at the low excitation energies (< 30 MeV) was obtained.