Synthesis of Super-Heavy Elements: Role of Uncertainty Analysis in Theoretical Modeling

Abstract : The existence of super-heavy elements (SHE) has been predicted by the nuclear shell model. However, the nuclear reaction theory for heavy systems, which is essential for the synthesis of SHE, has not been well established yet. Although we have reached a general agreement on the reaction mechanism, large discrepancies between quantitative predictions still persist because of the presence of the fusion hindrance phenomenon. The first aim of this Ph.D. work is to investigate different models associated with the complete description of the heavy-ion fusion-evaporation reaction. Then, a complete uncertainty analysis, in combination with a newlydeveloped cascade code called KEWPIE2, is performed. By inspecting uncertainties due to parameters and models, it is clearly revealed that the fission barrier has the most crucial role to play in constraining the fusion models. How to determine the uncertainty associated with the fission barrier? Since we do not have enough reliable data, we propose to consider Bayesian inference by reversing the usual mode of thinking. Based upon the KEWPIE2 code with simulated pseudo-data (without fusion hindrance), preliminary results tell us that the estimated uncertainty in the fission barrier appears to be quite sensitive to the number and precision of data points as well as the nuisance parameters. Furthermore, it is known that the fusion process and the fission barrier can be both described within the framework of the liquid-drop model. Thus, they should be correlated with each other. With the help of a simple liquid-drop mass formula and the regression theory, uncertainties in the model parameters as well as the correlation between the neutron-separation energy and fission barrier are inspected. The influence of their covariances on the survival probability is concretely investigated. Further consideration will be required to account for the correlation with the shell corrections.
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Hongliang Lu. Synthesis of Super-Heavy Elements: Role of Uncertainty Analysis in Theoretical Modeling. Nuclear Theory [nucl-th]. Université de Caen Normandie, 2015. English. ⟨tel-01235448⟩

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