Influence of neutron emission on the charge, mass and kinetic energy distribution of final fragments from ²³⁵U(n_th, f) reaction

Abstract

Using a Monte Carlo method we simulate an experiment that measures the mass, charge and kinetic energy of final fragments (after neutron emission) from the 235 U(n th , f) reaction. As input data for the simulation, for primary fragments (before neutron emission), we assume (i) a distribution of mass and kinetic energy; (ii) an average number of emitted neutron as a decreasing linear function of kinetic energy and (iii) for each mass, a constant yield of charges as a function of kinetic energy, equal to that obtained by W Lang et al for the highest measured kinetic energy window (108.5 MeV) which corresponds to the lowest measured excitation energy, that corresponds to the so called cold fission. The output of the simulation is the distribution of mass, charge and kinetic energy of final fragments. From this output we obtain that, for a given mass, the charge that has the highest yield in cold fission region has a yield obeying an increasing function of kinetic energy in all other region. Conversely, the yield of the less probable charge in cold fission is a decreasing function of kinetic energy in all other region. Our results of simulation suggest that, for two primary isobaric fragmentations with similar Q-value, the preference for more asymmetric charge splits (called Coulomb effect), observed in cold fission, is valid in all region, but neutron emission shadows this property in final fragments distribution.

Influence of Prompt Neutron Emission on the Final Distribution of Mass, Kinetic Energy, and Charge of Fragments from Actinide Fission

“…Lang et al obtained similar results for the reaction 235 U(n th , f) [16] which were interpreted by Montoya and Rivera with similar arguments [17]. See Figure 7.…”

“…The yield of charge as a function of kinetic energy for mass number 85 of final fragments (after neutron emission). (a) Results measured byLang et al [16]; (b) results from Monte Carlo simulation of the experiment[17].…”