ABSTRACT
There is now much experimental evidence proving without a doubt that fission isomers are in fact shape isomers, characterized by a very large prolate distortion ßi. The nuclear shape isomerism has been predicted by Hill and Wheeler on the basis of an analogy with molecular shape isomerism. Due to the specific shape with a maximum of the excitation function, the reactions with evaporation of two or more neutrons are very useful for isotopic assignment. In the crossed-reaction identification method, one tries to obtain the same isomer by bombarding various targets with different particles. The initial rising part of the excitation function for the radiative neutron capture and the correlation between delayed and prompt fission are explained by the existence of a potential barrier between the ground state and isomeric state, with a height close to the fission barrier. This barrier must be penetrated in order to populate the fission isomer.
