Ternary fission of uranium fissioning isomers, excited by neutrons

Spontaneously fissioning isomers (SFI) of uranium have been excited in the reactions 236,238U(n, n') at 4.5 MeV mean neutron energy. An electrostatic accelerator with pulsed beam and the time analysis of events have been used. The fission fragments were detected by the scintillation method. Detection of long-range particles was carried out by the ionization method. The relative probability of nuclear fission through the SFI states has been measured: (1.30±0.01)x10-4 (236U) and (1.48±0.02)x10-4 (238U). The decay half-lifes of the isomers have been determined: 121±2 ns (236U SFI) and 267±13 ns (238U SFI). Studying the ternary fission of the uranium SFI have been found that the probability of the process is one ternary per 163±44 binary fissions of 236U SFI and one ternary per 49±14 binary fissions of 238U SFI. Essential increase of the uranium SFI ternary fission probability as compared to the case of ternary fission of nuclei in nonisomeric states may be attributed to a specific nucleon configuration of uranium fissionable isotopes