A series of experiments on ternary nuclear fission were performed at the
Gatchina WWR-M neutron reactor. Two alternative approaches in description of the nuclear fission process were discussed in the 60s. Within the framework of the statistical fission model, descending from the saddle point was considered to be adiabatically slow, so that formation of the fragments occurs just before the scission point. On the contrary, in the dynamical model of fission the formation takes place at the barrier, and further separation of the fragments goes so rapidly that no significant redistribution of the fragment masses occurs. The ternary fission has occurred to be useful to tell between these two fission models.
The inclusive spectra of light nuclei (2,3H, 4,6,8,He, 7,8,9Li, 9,10,11Be, 11,12,13,14B, 14,15,16C, 20O) formed in the ternary fission were measured with a magnetic time-of-flight mass-spectrometer. The experiments were carried out with the 233U, 235U, 239Pu, and 242mAm targets exposed to thermal neutron fluxes. The next stage was the correlation experiment with a special setup which enabled simultaneous detection of the heavy fragments and the light nuclei 3H, 4He, 6He, 10Be. Detailed studies of the 235U and 239Pu thermal neutron induced fission, as well as spontaneous fission of 252Cf, were performed. As a result of these studies, the experimental data were obtained which created the basis for a detailed kinematics analysis aimed at determination of the initial conditions of the fragment separation. Such an analysis resulted in a rather large value (»
30 MeV) of the fragments initial energy. This value excludes the statistical model of nuclear fission.
(For more detail review see article "Ternary fission" in PNPI report of
the High Energy Physics Division "Main Scientific Activities 1971-1996").
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