Pre-equilibrium fission: a new decay channel for composite systems formed in fusion reactions

Abstract

When the fused composite system in a heavy ion collision has a fission barrier height comparable to its temperature, it can undergo fission in a very short interval of time of the order of 10^-21s before the formation of a fully equilibrated compound nucleus. In analogy with the well known pre-equilibrium particle emission in similar time scales, we call these fission events pre-equilibrium fission. Experimental signatures of this new mode of fission are demonstrated from an analysis of fragment angular distributions in a number of heavy ion induced fission reactions.