INTERMEDIATE STATES IN FISSION

Shell effects give rise to modulations in the liquid-drop fission barriers. For heavy nuclei with neutron number in the vicinity of 146-148, a two-humped barrier results, and the states of the secondary minimum act as intermediate states in the fission process. The existence of such states is reflected in subbarrier fission induced by neutrons in the resonance region, in the occurrence of broad resonance structures in the fission excitation functions, in anomalous fragment angular distributions and in the observed fission isomerism. Theoretical consequences of a two-humped fission barrier are developed and compared with experiment. © 1969.