Product yields for the photofission of 235U with 12-, 15-, 20-, 30-, and 70-MeV bremsstrahlung

The mass distributions for the photofission of 235U using bremsstrahlung with end-point energy of 12, 15, 20, 30, and 70 MeV were determined by γ spectrometry of fission product catcher foils. Smoothly varying curves without fine structure were obtained. A third hump in the symmetric region is not present. Several fractional independent chain yields in the mass region 126 --140 were measured and the corresponding most probable charges Z/sub p/(E/sub e/) were deduced. A comparison with the charge expected from the unchanged charge density hypothesis is made and an influence of the 50-proton shell on the behavior of the Z/sub p/ function is observed. Except in this mass region the determined Z/sub p/(E/sub e/) values are very well described by the empirical relation of Nethaway. From the isomeric ratios of 126Sb/sup g/-126Sb/sup m/, 128Sb/sup g/-128Sb/sup m/, and 131Te/sup g/-131Te/sup m/ average initial fragment spins are calculated using a statistical model analysis. The values increase with increasing end-point energy of the bremsstrahlung