Fission fragment mass and angular distributions were measured for ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ induced reactions on ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ at the laboratory energies of 180, 210, 250, and 266 MeV. By measuring the folding angle distributions between coincident fissionlike fragments at several beam energies it is shown that essentially the entire mass of the projectile is transferred to the composite system, which subsequently decays via symmetric fission. With increasing projectile energy the width of the mass distribution increases approximately as the square root of the nuclear temperature. The energy dependence of the angle integrated fusion-fission cross sections can be well described by classical trajectory calculations using the proximity potential and one-body dissipation. The fission fragment angular distributions become more anisotropic with increasing beam energy. Even at the lowest energy of 180 MeV, the angular distributions are more anisotropic than expected from statistical model calculations using saddle point shapes of the rotating liquid drop model. A simple parametrization of the angular momentum dependence of the effective moment of inertia gives a consistent description of the energy dependence of the angular distributions.

NUCLEAR REACTIONS Fusion, fission ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}({}_{}{}^{33}{}_{}{}^{}\mathrm{S}, f)$, $E=180-270\mathrm{}$ MeV, measured $\sigma \mathrm{}\left(E\right)\mathrm{}$, $\sigma \left(\theta \right)$, $\sigma \mathrm{}\left(M\right)\mathrm{}$. ${}_{}{}^{240}{}_{}{}^{}\mathrm{Cf}$ deduced effective moments of inertia.

• Received 3 February 1983

DOI:https://doi.org/10.1103/PhysRevC.28.747