Angular Distribution of Fragments from Fission Induced by Heavy Ions in Gold and Bismuth

We present the results of measurements of the angular distribution of fission fragments produced by irradiation of ${\mathrm{Au}}^{197}$ and ${\mathrm{Bi}}^{209}$ with various heavy ions. The projectiles, ${\mathrm{B}}^{11}$, ${\mathrm{C}}^{12}$, ${\mathrm{N}}^{14}$, and ${\mathrm{O}}^{16}$, had energies from a few MeV above the Coulomb barrier to 10.4 MeV per nucleon. The gross features of these results can be explained by use of a model and parameters that have been used by others to account for angular distributions of fission fragments from helium-ion bombardments. In detail, however, these results appear to indicate that the models used to predict the average value of the angular momentum of the compound nucleus give values too low near the Coulomb barrier. Furthermore, at high bombarding energies it is necessary to consider the fact that appreciable direct interaction is taking place.