Transition state rates and mass asymmetric fission barkers of compound nuclei Mo-90,Mo-94,Mo-98

Excitation functions were measured for complex fragments with atomic number Z = 5-25 emitted from the compound nuclei Mo-90,Mo-94,Mo-98 produced in th e reactions Kr-78,Kr-82,Kr-86 + C-12. Mass-asymmetric fission barriers were extracted by fitting the excitation functions with a transition state form alism. The extracted barriers are several MeV higher on average than the ca lculations of the Rotating Finite-Range Model and substantially lower than predicted by the Rotating Liquid Drop Model. The symmetric fission barriers measured support the hypothesis of a congruence term that doubles for the fission of strongly indented saddle-point shapes. The excitation functions were analyzed to search for atomic number Z- and energy E-dependent deviati ons from transition-state-method predictions. All of the measured excitatio n functions can be scaled onto a single universal straight line according t o the transition-state predictions. No Z- and/or E-dependent effects that c ould be attributed to transient effects are visible. (C) 1999 Elsevier Scie nce B.V.