Charge and mass distributions of the photofission fragments on the targets ²³⁸U, ²³² Th and ¹⁸¹Ta at low and medium electron energies ( 50 MeV and 3500 MeV) have been measured by using activation method. The cross sections are used to extract fission fragment yields, as function of excitation energy of the fissioning nucleus, thereby affording an opportunity to follow the transition from asymmetric to symmetric mode fission in the investigated targets. The mass yields of fission products were deduced from measured cross sections and fitted of unmeasured ones with standard formulation of the fragment charge distribution in Gaussian form. The total photofission cross section per equivalent quanta was obtained by summing up all mass curve. For U at the energy 50MeV we have obtained the value 182.55? 36.5 mb and for Th 47.25? 7.08 mb. At 3500 MeV the photofission cross sections per equivalent quanta were equal to 274.8? 35 mb and to 145.36? 21.8 mb respectively The different mode yields have been calculated by the decomposition of the mass curves in termes of five-Gaussian fit, taking into account two modes for asymmetric fission Correlation between these components allowed to estimate the contribution of symmetric fission with increasing excitation energy. It was fond that asymmetric fission dominated at low photon energy and symmetric fission increases with energy growth. Ratio of the yields asymmetric and symmetric fission for U target was equal to 10.2? 1.02 at 50 MeV, and 2.5 ? 0.25 at 3500 MeV . For Th the same ratio was equal to 13.22? 1.98 and 3.2 ? 0.48 at 50 MeV and 3500 MeV respectively. These results are in good agreement with previous experimental data In Ta target was observed the symmetric mode only, which was equal to 0.81? 0.12 mb at 3500 MeV and have the upper limit value equal to 0.09 mb at 50 MeV. In frames of several models the total fission cross section was described as the sum of cold and warm fission events, where the notation refer to fission for which the post -cascade nuclei were left with low and high excitation energies. In this way the asymmetric fission occurs almost entirely in the cold branch while in the warm branch the symmetric fission mode gives the essential contribution.

An information, associated with charge and mass distributions of fission fragments, have been determined in connection of the excitation energies of fissioning nuclei also. The most probable charge Z_p of the charge distribution have changed with increasing excitation energy for light asymmetric and symmetric peaks of the fission products, and remains approximately constant for heavy fission fragments. The dispersion of mass distributions increased with photon energy. The yields of the light elements (Z? 26, А ? 59) have been measured also. These data allowed to receive the estimation of the triple fission contribution and to provide the energy dependence of this mode in range from giant resonance to high energy. The estimates of the triple to binary fission yield ratio indicate the relative growth from value 10^-5 to 10^-3 with energy increasing .