Effect ofPu240Compound-Nucleus State on the Fission-Fragment Mass and Kinetic Energy Distributions

Fission-fragment mass and kinetic energy distributions have been obtained for fission of ${\mathrm{Pu}}^{239}$ induced by neutrons filtered through beryllium and by neutrons filtered through samarium. The beryllium filter enhances the contribution of the negative-energy resonance level to the fission cross section, and the samarium filter enhances the contribution of the 0.297-eV level. Surface-barrier detectors were used for the simultaneous measurement of both the fragment energies. Absolute fragment energies were calculated by using mass-dependent pulse-height energy relations.