First direct measurement of isotopic fission-fragment yields of 239U
Abstract
A direct and complete measurement of isotopic fission-fragment yields of 239U has been performed for the first time. The 239U fissioning system was produced with an average excitation energy of 8.3 MeV in one-neutron transfer reactions between a 238U beam and a 9Be target at Coulomb barrier energies. The fission fragments were detected and isotopically identified using the VAMOS++ spectrometer at the GANIL facility. This measurement allows to directly evaluate the fission models at excitation energies of fast neutrons, relevant for next-generation nuclear reactors. The present data, in agreement with model calculations, do not support the recently reported anomaly in the fission-fragment yields of 239U and confirm the persistence of spherical shell effects in the Sn region at excitation energies exceeding the fission barrier by few MeV.