Consequences of fission deexcitation of compound nuclei formed in heavy-ion reactions

Restrictions on cross sections of compound nuclei surviving fission during the dexcitation process are investigated for a variety of heavy-ion projectile-target combinations. Calculations are performed within the framework of the Bohr-Wheeler model using angular-momentum-dependent fission barriers calculated from the rotating liquid drop model of Cohen, Plasil, and Swiatecki. It is shown that fission severely limits the cross sections of evaporation residue products at higher bombarding energies, that the critical angular momenta of such a model slowly increase with increasing bombarding energy, and that these critical angular momenta are very much lower than the values at which the fission barrier is thought to disappear. Calculated cross sections are in reasonable agreement with several experimental excitation functions. Experimental results are also compared with limits on fusion cross sections resulting from entrance conditions and comparisons are made between the consequences of the two types of models---entrance condition limits and fission-imposed limits on evaporation residue products.NUCLEAR REACTIONS Calculated evaporation residue σ(E). HI projectiles ¹¹B to ⁸⁴Kr, targets ¹⁰B to ¹⁶⁵Ho, compound nuclei ⁴³Sc to ²¹¹Ac, E=3.5-10.5 MeV/nucleon. Deduced critical J.