Abstract
Prompt neutron multiplicity distributions ν(A) are required for prompt emission correction of double energy (2E) measurements of fission fragments to determine pre-neutron fragment properties. The lack of experimental ν(A) data especially at incident neutron energies (En) where the multi-chance fission occurs impose the use of ν(A) predicted by models. The Point-by-Point model of prompt emission is able to provide the individual ν(A) of the compound nuclei of the main and secondary nucleus chains undergoing fission at a given En. The total ν(A) is obtained by averaging these individual ν(A) over the probabilities of fission chances (expressed as total and partial fission cross-section ratios). An indirect validation of the total ν(A) results is proposed. At high En, above 70 MeV, the PbP results of individual ν(A) of the first few nuclei of the main and secondary nucleus chains exhibit an almost linear increase. This shape is explained by the damping of shell effects entering the super-fluid expression of the level density parameters. They tend to approach the asymptotic values for most of the fragments. This fact leads to a smooth and almost linear increase of fragment excitation energy with the mass number that is reflected in a smooth and almost linear behaviour of ν(A).
Highlights
Nowadays there is an interest in the study of neutroninduced fission at intermediate and high energies, justified by the need of nuclear data for both the better understanding of the fission process and new applications, e.g. advanced nuclear systems based on fission, incineration of nuclear waste, isotope production etc
The ν(A) shape and its evolution with increasing En is important on one side for applications and on the other hand for a better understanding of the prompt emission at high En
At high excitation energies a damping of shell effects occurs, the level density parameters of a great part of fragments tending to the asymptotic values. This fact leads to an almost smooth and linear increase of the fragment excitation energy with the mass number having as consequence a smooth and almost linear behaviour of individual ν(A)
Summary
Nowadays there is an interest in the study of neutroninduced fission at intermediate and high energies, justified by the need of nuclear data for both the better understanding of the fission process and new applications, e.g. advanced nuclear systems based on fission, incineration of nuclear waste, isotope production etc. Because the present ν(A) results, as well as those of other models and procedures used to recover the preneutron fragment data, are predictions (e.g. ν(A) provided by the scaling procedure [3] and the GEF code [4], already c The Authors, published by EDP Sciences The ν(A) shape and its evolution with increasing En is important on one side for applications and on the other hand for a better understanding of the prompt emission at high En. The evolution of the shapes of individual ν(A) (corresponding to the fissioning compound nuclei involved at the respective En) with increasing En is explained by the influence of shell effects of the fragments. This fact leads to an almost smooth and linear increase of the fragment excitation energy with the mass number having as consequence a smooth and almost linear behaviour of individual ν(A)
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