Angular Anisotropy and the Structure of the Fission Barrier

The authors report on measurements of the angular distributions of fragments produced in the neutron-induced fission of 232Th, 238U, 237Np, 238Pu, 240Pu, 242Pu and 241Am target nuclei and photon-induced fission of 232Th, 238U, 238Pu, 240Pu and 242Pu target nuclei. The (n, f) reaction was investigated using electrostatic generators of the Institute of Physics and Power Engineering, while the photofission reaction was studied with the help of the 12-MeV mictrotron at the Institute of Physical Problems. Particular attention is paid to excitation energies near the threshold. The experimental data do not fit the traditional picture of fission probability, but can be satisfactorily explained in terms of double-humped barrier concepts. In discussing the results of the measurements, the authors touch on the quasi-stationary states of the nucleus in the second valley, the structure of barriers, even-odd differences in fission probability, and the question of the penetration probability at certain energies in the case of highly deformed nuclei. (author)