Fission fragment angular distributions for ¹¹B and ¹⁹F+²³⁸U systems

Abstract

The fission fragment angular distributions were measured at energies above the fusion barrier, for the systems ¹¹B and ¹⁹F + ²³⁸U. An analysis of the present data along with those already available for the systems ^6,7Li, ¹²C, and ¹⁶O + ²³⁸U was made in terms of the saddle-point statistical model. While the anisotropies were "normal" for ^6,7Li, ¹¹B, ¹²C+²³⁸U systems, the ones for ¹⁶O and ¹⁹F+²³⁸U systems were found to be "anomalous." The entrance channel mass asymmetry dependence of the anisotropies as observed here is consistent with the expectations of preequilibrium fission dynamics. This result emphasizes the importance of preequilibrium fission in heavy-ion induced fusion-fission reactions.