Velocities of Fragments from Fission of U233, U235, and Pu239

Abstract

The velocity distributions of fragments from slow neutron induced fission have been measured by a time-of-flight method. When compared with data from fission fragments stopped in ionization chambers filled with argon and carbon dioxide, these velocity data indicate that the kinetic energies of the fragments exceed those reported by ionization chamber measurements by 5.7 Mev for the most probable light fragment and by 6.7 Mev for the most probable heavy fragment. These energy differences, for the most probable light and heavy fragments, can be explained by energy-ionization ratios which exceed by 6 percent and 11 percent, respectively, the alpha-particle energy-ionization ratio on which the energies from ionization chamber measurements are based. The average kinetic energy of fission fragments determined from velocities is shown to be in good agreement with calorimeter results and the energy calculated from recent mass spectrographic data.