Fragment Energy Correlation Measurements forCf252Spontaneous Fission andU235Thermal-Neutron Fission

Fission-fragment mass and energy distributions and mass-versus-energy correlations have been obtained for ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ spontaneous fission and ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$ thermal-neutron-induced fission. Silicon surface-barrier detectors were used in energy correlation measurements; absolute fragment energies were obtained by means of the mass-dependent energy calibration developed recently at this laboratory. Average total fragment kinetic energies before neutron emission are found to be 186.5±1.2 MeV for ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ and 171.9±1.4 MeV for ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$. Detailed experimental results are given and compared with those of other experiments. Observed fine structure in the fragment mass distribution and in the average total fragment kinetic energy as a function of mass is correlated with the energetically preferred even-even nucleon configurations in the fragments. New determinations of the root-mean-square width of the total-kinetic-energy distribution as a function of mass show structure which is also correlated with the energetically preferred even-even fragment configurations. Fission-neutron and gamma-ray data of other experiments are used with the new fragment kinetic energies presented here to examine the total energy balance for fission for the two cases studied.