Study of fission of $sup 233$U and $sup 235$U induced by thermal neutrons

Yield of fission events, N, is studied as function of pair fragment energies E/saub 1, E/sub 2/, at fission of /sup 233/U and /sup 235/U induce d by thermal neutrons. The fragment energies were registered in a double ionization chamber with meshes. The peak/dip ratios in the mass distributions, not corrected by account of the resolution and the neutron emission, for /sup 233/U and /sup 235/U are found to have values, averaged over several series, of 300 and 350, respectively. The initial N(E/sub 1/, E/sub 2/) distributions were transformed to N(E/sub k/, mu ) where mm is the fragment mass, obtained with no account of a neutron emission, and E/sub k/ is the total fragment kinetic energy. Sequences of the energy and mass spectra as functions of mu and E/sub k/ are presented. The shape of the energy spectra have some peculiarities: besides the main bumps there are some peaks of essentially less intensity. In the region of mass symmetry the mean energy of these peaks is 120-- 130 MeV, while in the region of strong asymmetry it is uniform and in some cases may be represented as superpositions of several more narrow components. This structure effect is still moremore » manifested in the fragment mass spectra. Possible reasons of these phenomena are discussed. The basic properties of the energy distributions are compared with those by other authors. The maximum-- minimum difference for E/sub k/ in the case of /sup 233/U in the symmetric mass region is found to be 18 plus or minus 2 MeV. (auth)« less