High mass-asymmetry distributions of fissioning nuclei

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Abstract
It is shown that new mass-asymmetry valleys appear in the fragmentation potential V(l, eta ) as function of the length l and mass-asymmetry coordinate eta =(A1-A2)/(A1+A2) at larger values of eta . These valleys are due to a correct treatment of the shell effects such that for separated fragments the shell effects equal the sum of the shell effects of the individual fragments and correspond to the double magic fragments 48Ca, 78Ni, 132Sn and 208Pb or maybe 56Ni. It is also shown that the fission mass distributions have additional peaks corresponding to the bottom of these new valleys. The calculations are illustrated for 252No and 238U. The preliminary results show relatively high percentage yields for 238U, in agreement with present available experimental data.