Similarities and differences in fission and evaporation of hot nuclei and hot metallic clusters

Similarities and differences in the decay of hot nuclei and hot metallic clusters are discussed. A liquid-drop model description explains why symmetric fission is the dominant decay mode for heavy nuclei, whereas hot metallic clusters prefer strongly asymmetric fission, which looks more like an evaporation process of light charged particles. Critical (appearance) sizes of multiply-charged clusters are calculated by equating the rates for neutral monomer and charged-particle evaporation. The time scale of cluster decay due to multiple-cluster atom emission is determined by calculating shrinking and cooling rates. It is compared with the time scale of particle emission during fission of hot nuclei, where friction plays a crucial role. It is probable that viscosity is also of importance in symmetric fission of clusters. The latter is predicted to be possible due to shell effects, in particular for clusters with closed shells. The increase (as compared to a purely statistical model description) of fission times of clusters due to friction is predicted to be an order of magnitude larger than the corresponding well established effect in fission of hot nuclei. (author)