Comparison of the energy and mass characteristics of the /sup 239/Pu(n/sub th/,f) and the /sup 240/Pu(sf) fragments

The energy and mass distributions and their correlations have been studied for the spontaneous fission of /sup 240/Pu and the thermal neutron induced fission of /sup 239/Pu. A comparison of the /sup 240/Pu(sf) and the /sup 239/Pu(n/sub th/,f) results shows a narrower mass distribution, a much higher peak yield, a much lower symmetric fission yield, and a more pronounced fine structure for the spontaneous fission than for the neutron induced fission. The average total kinetic energy is 1.3 MeV higher for /sup 240/Pu(sf) than for /sup 239/Pu(n/sub th/,f), and also the energy-mass correlations behave differently in both cases. All these results are discussed and interpreted in the framework of the scission point model of Wilkins et al. Finally, the damping of the /sup 240/Pu fission mode below the barrier is demonstrated.