Fission fragment energy correlation measurements for the thermal neutron fission of 239Pu and 235U

Fission fragment mass and kinetic energy distributions and mass-versus-energy correlations have been measured for the thermal neutron induced fission of 239Pu and 235U. Unwanted events were eliminated by a coherence test based on time of flight. The global mass distribution for 239Pu shows much weaker fine structure than 235U. However, for events with high total kinetic energy this fine structure becomes more prominent and the yield of mass 135 dominates for 239Pu compared to mass 134 for 235U. Moreover, a prolate deformation for mass 102 in the 134/102 mass ratio for 235U is compatible with the data. The results show that Esub(K)(μsub(H)), hence Esub(L) and/or Esub(H) for 239Pu and 235U in the high mass yield regions have low energy tails produced in the act of fission. Furthermore, the data suggest that most of the proton pairs are broken after the effective determination of the structure of the nascent fragments and probably just before and/or in the act of scission itself. (Auth.)