The yields of 28 mass chains have been measured for fission of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$ and ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ induced by neutrons at four different energies from 6.0 to 9.1 MeV. This is the first experimental measurement where sufficient energy resolution was obtained to observe the effect of the onset of second chance fission in the case of symmetric fission. The ${}_{}{}^{111}{}_{}{}^{}\mathrm{Ag}$ and ${}_{}{}^{112}{}_{}{}^{}\mathrm{Pd}$ results are compared with measurements at other neutron energies and with previous theoretical predictions. All nuclide results are presented in tabular form, as a function of neutron energy. The mass chains measured range from 84 to 156.

NUCLEAR REACTIONS, FISSION ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}\mathrm{}(n,f)\mathrm{}$ and ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}\mathrm{}(n,f)\mathrm{}$, $E=6.0,7.1,8.1,9.1\mathrm{}$ MeV; measured yields of 28 mass chains.

• Received 7 November 1977

DOI:https://doi.org/10.1103/PhysRevC.17.1089