Variation with Neutron Energy of the Yield of High-Kinetic-Energy Fragments from U233 , U235 , and Pu239

A fission chamber has been devised which detects with high efficiency those fission events in which the kinetic-energy release of the heavier binary fragment is maximal. This detector has been used, in conjunction with a conventional fission detector (whose efficiency is independent of fragment energy), in a study of the relative yield of high-kinetic-energy fission of $^{233}\mathrm{U}$, $^{235}\mathrm{U}$, and $^{239}\mathrm{Pu}$, induced by low-energy neutrons. The variations in the yield of high-kinetic-energy fragments shows a qualitative correlation with results of measurements of the relative symmetric fission yield as a function of neutron energy. The results indicate that an increase in symmetric fission is accompanied by an increased yield of certain high-kinetic-energy fragments. Such behavior shows that the fission process is more complex than has generally been assumed.