Excitation functions and mass asymmetric fission barriers for compound nuclei Se-70,Se-76

Excitation functions were measured for complex fragments with atomic number Z = 5-20 emitted from the compound nuclei Se-70,Se-76 produced in the reac tions Ni-58,Ni-64 + C-12. Mass asymmetric fission barriers were extracted b y fitting the excitation functions with a transition state formalism. The e xtracted barriers were compared with those calculated from macroscopic nucl ear models. The measured barriers for symmetric fission seem to support the hypothesis of a shaped-dependent congruence energy, which doubles for fiss ion of strongly indented saddle-point shapes. All of the measured excitatio n functions can be scaled onto a single straight line according to the tran sition state prediction. (C) 2000 Elsevier Science B.V. All rights reserved .