Spontaneous Fission ofPu240: Comparison with the Slow-Neutron-Induced-Fission ofPu239

Fission-fragment mass and kinetic energy distributions have been obtained for the spontaneous fission of ${\mathrm{Pu}}^{240}$ and compared with those for the thermal-neutron-induced fission of ${\mathrm{Pu}}^{239}$ reported previously. Surface-barrier detectors were used for the simultaneous measurements of energies of both the fission fragments. Absolute fragment energies were calculated by using mass-dependent pulse-height energy relations. The measured average total kinetic energies were found to be 177.3 ± 1.5 MeV and 173.0 ± 1.5 MeV for the spontaneous and the induced fission, respectively, and the average pre-neutron total kinetic energies were 178.9 ± 1.5 MeV and 175.2 ± 1.5 MeV, respectively. The measured mass distribution for the spontaneous fission appears to be significantly different in shape from that for the induced fission.