CNRS Université Bordeaux

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General model description of fission observables


CENBG, Chemin du Solarium B.P. 120, 33175 Gradignan, France

Abstract : Structural effects in fission-product yields and neutron data for a large number of fissioning nuclei between 220Th and 262Rf from spontaneous fission to 14- MeV-neutron-induced fission have been used to deduce information on the properties of the fissioning systems. Macroscopic properties are attributed to the compound nucleus, while fission channels are ascribed to shells in the nascent fragments. Using a recent general empirical description of the nuclear level density and assuming different characteristic time scales for the collective degrees of freedom of the fissioning system, a new fission model has been developed. The model combines the statistical concept of the scission-point model of Wilkins et al. with empirically determined properties of the potential-energy surface and some characteristic dynamical freeze-out times. The recently discovered energy-sorting mechanism in superfluid nuclear dynamics determines the sharing of intrinsic excitation energy at scission and the enhancement of even-odd structure in asymmetric splits. The model reproduces all measured fission yields and neutron data rather well with a unique set and a relatively small number of free parameters. Since the parameters of the model are closely related to physical properties of the systems, some interesting conclusions on the fission process can be deduced. Prospects for the predictive power of this approach for hitherto unknown fissioning systems are discussed.

Keywords : Fission-fragment yields ; fission channels ; fission dynamics ; macroscopic-microscopic approach ; separability principle ; energy sorting ; even-odd effect.

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