General view on the progress in nuclear fission : a review

Abstract : An overview is given on some of the main advances in experimental methods, experimental results and theoretical models and ideas of the last years in the field of nuclear fission. New approaches extended the availability of fissioning systems for experimental studies of nuclear fission considerably and provided a full identification of all fission products in A and Z for the first time. In particular, the transition from symmetric to asymmetric fission around 226 Th and some unexpected structure in the mass distributions in the fission of systems around Z = 80 to 84 as well as an extended systematics of the odd-even effect in fission fragment Z distributions have been measured. Three classes of model descriptions of fission presently appear to be the most promising or the most successful ones: self-consistent fully quantum-mechanical models, stochastic models, and a new semi-empirical model description. The first ones are the only ones that fully consider the quantum-mechanical features of the fission process. Unfortunately, the most advanced models in nuclear physics that have been developed for stationary states are not readily applicable to the decay of a meta-stable state. Intense efforts are presently made to develop suitable theoretical tools. Moreover, the technical application of the most advanced models is heavily restricted by their high demand on computer resources. Stochastic models provide a fully developed technical framework. The 1 main features of the fission-fragment mass distribution were well reproduced from mercury to fermium and beyond. However, the limited computer resources still impose severe restrictions, for example on the number of collective coordinates. In an alternative approach, considerable progress in describing the ob-servables of low-energy fission has been achieved by exploiting powerful theoretical ideas based on fundamental laws of mathematics and physics. This approach exploits (i) the topological properties of a continuous function in multidimensional space, (ii) the separability of the influences of fragment shells and macroscopic properties of the compound nucleus, (iii) the properties of a quantum oscillator coupled to the heat bath of the other nuclear degrees of freedom for describing the fluctuations of normal collective modes, and (iiii) an early freeze-out of collective motion to consider dynamical effects. This new approach reveals a high degree of regularity and allows calculating high-quality data that are relevant for nuclear technology without specific adjustment to experimental data of individual systems.
Type de document :
Pré-publication, Document de travail
2016
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  • HAL Id : in2p3-01314814, version 1

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Karl-Heinz Schmidt, Beatriz Jurado. General view on the progress in nuclear fission : a review. 2016. 〈in2p3-01314814〉

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