Investigation of the heavy nuclei fission with anomalously high values of the fission fragments total kinetic energy

Institute of Physics and Power Engineering, 1, Bondarenko sq., Obninsk 249030, Russia

^* e-mail: hva@ippe.ru

Published online: 6 March 2018

Abstract

Binary fission of ²³²Th and ²³⁸U induced by fast neutrons were under intent investigation in the IPPE during recent years. These measurements were performed with a twin ionization chamber with Frisch grids. Signals from the detector were digitized for further processing with a specially developed software. It results in information of kinetic energies, masses, directions and Bragg curves of registered fission fragments. Total statistics of a few million fission events were collected during each experiment. It was discovered that for several combinations of fission fragment masses their total kinetic energy was very close to total free energy of the fissioning system. The probability of such fission events for the fast neutron induced fission was found to be much higher than for spontaneous fission of ²⁵²Cf and thermal neutron induced fission of ²³⁵U. For experiments with ²³⁸U target the energy of incident neutrons were 5 MeV and 6.5 MeV. Close analysis of dependence of fission fragment distribution on compound nucleus excitation energy gave us some explanation of the phenomenon. It could be a process in highly excited compound nucleus which leads the fissioning system from the scission point into the fusion valley with high probability.