Energetics of the fission of ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$ induced by 8.5- and 13-MeV protons and of ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ induced by 12-MeV protons have been studied by means of a three-parameter experiment in which the time of flight of one fragment and the energies of both fragments are measured. The average number of neutrons emitted from the individual fragments and from both fragments together are obtained as functions of fragment mass and total kinetic energy. The number of neutrons emitted per fragment generally increases with increasing fragment mass, and the "sawtooth" shape characteristic of neutron emission in low-excitation fission is still apparent, although the relative depths of the minimum in each of the present cases is reduced. A comparison of the number of neutrons emitted as a function of fragment mass for 8.5- and 13-MeV proton-induced fission of ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$ shows that excitation energies of the light fragments change only slightly, while those of the heavy fragments increase significantly with increasing bombarding energy. The largest change occurs in the mass region at about 132 amu, where the doubly-closed-shell configuration $Z=50\mathrm{}$, $N=82\mathrm{}$ occurs. Pre- and post-neutron-emmission fragment mass distributions are obtained, together with the fragment energy distributions and mass-versus-energy correlations. Energy balance is studied by comparing the total energy available for fission into a given mass pair with the sum of the fragment excitation energies, calculated from neutron emission data and mass tables, and the measured fragment kinetic energies. The results are discussed within the framework of simple theoretical fission models.

• Received 28 December 1970

DOI:https://doi.org/10.1103/PhysRevC.3.2034