Isotopic fission yields of ${}^{240}$Pu as a function of the excitation energy

Abstract

Complete isotopic fission yields distributions of $^{240}$Pu have been measured as a function of the initial excitation energy. The $^{240}$Pu fissioning system was produced through a two-proton transfer reaction between a $^{238}$U beam and a $^{12}$C target. The reaction was measured in inverse kinematics at Coulomb barrier energies, allowing for the full distribution of fission fragments to be isotopically identified with the VAMOS++ Spectrometer. The excitation energy of the system was measured on an event-by-event basis by detecting the target-like recoil $^{10}$Be in a segmented silicon telescope. This manuscript reports on the evolution of the fission yields as a function of the excitation energy of the system between 8.2 to 11.9 MeV. The influence of the excitation energy is manifested in the damping of shell effects that feed the yields in the symmetry valley, as well as in a reduction of the neutron content of the fragments. This reduction, however, is observed only in the heavy fragment, while the neutron content of the light fragment remains unaffected. The comparison with previous measurements, models, and evaluations highlights the importance of correlated observables for improving fission models.