Role of the rearrangement time in nuclear fission

The two-step model of nuclear fission is based on the representation of fissile nuclei as dinuclear systems, which can change into new dinuclear systems. Arguments are presented in favour of rearrangement times in fission as short as 1.1 10-25 second. A comparison is made with the shortest rearrangement times encountered in chemical diatomic molecules, where femtosecond pulse lasers are in current use, e.g. 0.4 10-18 s expected in HCl. Consequences of so-short reaction times in fission, in particular the uncertainty in mass and charge of the fission fragments, are discussed. The narrowly- symmetric mass spectrum of 258Fm (s.f.) can be explained as resulting from Coulomb-barrier-free fission events. 1. G. Mouze and C. Ythier, Nuovo Cimento A 103 (1990)617; 2. G.Mouze, Varenna Conference, June 2006, Uni. Milano, in press; 3. A. H. Zewail, Nobel Lecture 1999;4.D.C. Hoffman et al., Los Alamos Report LA-UR 677, 2901 (1977). (orig.)