Shells, Anti-Shells and Modes in nuclear Fission

Abstract

Fission phenomena are surveyed where fragment properties are catching the eye. Beyond the Liquid Drop the relevant properties of fragments are shell effects and nuclear pairing. Shell effects influence on mass, charge, stability and deformability of fragments. Most often only the stabilizing effects of shells are discussed and the equally frequent destabilizing effects are not mentioned. For the present purpose the terms shells and anti-shells are used in case of stabilizing and destabilizing effects, respectively. Fragment shells and anti-shells lead to fission modes with characteristic properties. A special issue is where in the course of fission these modes assume their characteristic features. Surprisingly fragment angular distributions in above- and sub-barrier fission help elucidating this question. The discussion is focussed on fission in the standard actinides.