Independent yields from the photofission of 232Th, and the Zp and statistical-dynamic models.

Abstract

Independent fission yields were measured for $^{82}\mathrm{Br}$, $^{96}\mathrm{Nb}$, $^{124}\mathrm{Sb}$, and $^{126}\mathrm{Sb}$ produced by photofission of $^{232}\mathrm{Th}$ with 27-MeV peak bremsstrahlung and for $^{136}\mathrm{Cs}$ at 11, 15, and 27 MeV. Upper limits for the independent yields for $^{86}\mathrm{Rb}$ and $^{134}\mathrm{Cs}$ and mass yields for mass chains 125 and 127 were also measured for $^{232}\mathrm{Th}$ photofission at 27 MeV. Various extensions of the ${\mathit{Z}}_{\mathit{p}}$ charge-distribution model were found to give generally good agreement with experimental measurements in the asymmetric mass regions, but less satisfactory agreement in the symmetric region. A statistical charge-distribution model incorporating post-fission dynamics correlated well with experimental values in both symmetric and asymmetric regions. The statistical-dynamic model naturally predicted pairing and shell effects which were in good agreement with experimentally observed effects. One important outcome of the statistical-dynamic model calculations was the production of a linear shape on the wings of the charge-distribution curve when proximity proton transfer after scission was incorporated into the model. Such linear shapes have previously been experimentally observed without explanation.