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

Vitaly Khryachkov,Vecheslav Mitrofanov,Alexei Sergachev,Vladimir Ketlerov,Andrei Goverdovskii,F.-J Hambsch,N Carjan,I Ruskov

doi:10.1051/epjconf/201816900011

Vitaly Khryachkov, Vecheslav Mitrofanov + Show 6 more

Open Access

https://doi.org/10.1051/epjconf/201816900011

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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.

Highlights

We would like to point out some particular cases of nuclear fission when fission fragments appeared to have no excitation energy, at equilibrium deformation
Where Q is the energy of nuclear fission, Bn is the neutron binding energy in the fissile nucleus, and En is the neutron kinetic energy
In the case of cold fragmentation this stage of the fission process is omitted, because of at the saddle point the nucleus transforms into two fission fragments in the ground state

Summary

Introduction

We would like to point out some particular cases of nuclear fission when fission fragments appeared to have no excitation energy, at equilibrium deformation. Two-dimensional spectrum with axis of fragment mass versus TKE for incident neutron energy of 5 MeV is shown in Fig. 2 (left).

Results

Conclusion