Fission-fragment mass and energy distributions and mass-versus-energy correlations have been obtained for ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$ and ${}_{}{}^{241}{}_{}{}^{}\mathrm{Pu}$ thermal-neutron-induced fission. Silicon surface-barrier detectors were used in energy-correlation measurements; absolute fragment energies were obtained by means of a recently developed mass-dependent energy calibration. Average total fragment kinetic energies before neutron emission are found to be 177.7±1.8 MeV for ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$ and 179.6±1.8 MeV for ${}_{}{}^{241}{}_{}{}^{}\mathrm{Pu}$. 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 fragment mass show structure which also appears to be 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. A comparison of the two mass distributions shows the heavy-fragment groups almost superimposed; the light-fragment groups are separated almost uniformly by 2 amu.

• Received 4 April 1966

DOI:https://doi.org/10.1103/PhysRev.149.894