Photofission of 238U with neutron-capture gamma rays

Fission yields from the photofission of 238U with neutron capture γ rays were measured at an effective excitation energy E/sub x/ = 7.8 MeV. The mass distribution of the fission fragments was deduced by measuring yields of 19 mass chains with respect to 135Xe, whose cumulative yield was measured directly. The results are in general agreement with those obtained by Jacobs et al. using bremsstrahlung at higher energies. However, a systematic decrease of the yields of a few mass chains was observed. This decrease can be attributed to a change in the shape of the light and heavy mass distributions, as a function of energy. The ratio GAMMA/sub n//GAMMA/sub f/ was measured at two energies and its values confirm recent theories on the shape and height of the second fission barrier in 238U. The most probable charge Z/sub p/ was obtained for the mass chains 92, 134, and 135 at three energies