Coincident Time-of-Flight Measurements of the Velocities ofCf252Fission Fragments

The primary object of the experiment was to improve the absolute accuracy of the determination of the mean values of the distributions in fragment velocity, mass, and kinetic energy. Absolute uncertainties attained are estimated to be about ±0.5% for the velocity measurements (∼±1% for the energy measurements); statistical uncertainties on the distribution mean values are considerably smaller. Mean velocities of 1.036 and 1.375 cm/nsec, mean mass numbers of 143.61 and 108.39 amu, and mean kinetic energies of 80.01 and 105.71 MeV, respectively, were obtained for the heavy- and light-fragment groups. The mean total-fragment kinetic energy was found to be 185.7 MeV, and the mean mass ratio, 1.334. Perturbations, suggesting fine structure, are found in the primary mass yields. Associated perturbations are observed in the average total-fragment kinetic energy $〈E_K\left(R_A\right)〉$ for the corresponding mass divisions. A decrease in $〈E_K\left(R_A\right)〉$ near symmetric mass division, extending over five or six mass pairs and reaching about 20 MeV at a mean mass ratio of 1.0, was observed; but the absolute uncertainty is large.