Fission of polonium, osmium, and erbium composite systems

Fission cross section excitation functions were measured from near threshold to {~}10 MeV/nucleon using ⁹Be, ¹²C, 16,18O, 24,26Mg, ³²S, and ⁶⁴Ni beams. The systems studied included ²¹⁰Po formed in ¹²C and ¹⁸O induced reactions; ¹⁸⁶Os formed in ⁹Be, ¹²C, ¹⁶O, and ²⁶Mg reactions; and ¹⁵⁸Er formed in ¹⁶O, ²⁴Mg, ³²S, and ⁶⁴Ni reactions. In addition, the composite systems 204,206,208Po formed with ¹⁶O and ¹⁸O projectiles were studied. In the experiment the velocities and emission angles of two coincident fission fragments were measured using position-sensitive multiwire proportional counter stop detectors and a thin ({~}200 {μ}g/cm²) gas "start" detector. The measured fission excitation functions along with previous data from ⁴He and ¹¹B bombardments for the ¹⁸⁶Os and ²¹⁰Po systems and recent data on the ²⁰⁰Pb system are compared to statistical model calculations using recent angular momentum dependent fission barriers calculated by Sierk. Comparisons of calculated and measured fission excitation functions show good overall agreement between data and theoretical predictions. These comparisons give good agreement for both a wide range of mass of the composite system and for a wide range of mass asymmetry in the entrance channel. It is concluded that the fission barriers of Sierk give a good description of both the mass and angular momentum dependence of fission barriers in this region.