Abstract
To improve the evaluation of nuclear observables, refined models are to be used more and more as underlying analysis tools. Fission is a complex process and is the less accurately described with current models. Standard evaluation models rely on the Hill-Wheeler formalism for the fission transmission coefficient, which in turns is based on phenomenological parameters “reflecting” the fission barrier heights and widths. To reduce the weight of phenomenology in the evaluation process, nuclear structure models are expected to embed more and more microscopic descriptions. As models are rarely exact, evaluators are often compelled to “tune” model parameters so that observables can be properly reproduced. Related computation time can thus be a major hindrance to the use of advanced models in evaluation as final adjustments are expected to remain necessary. For this reason, a macroscopic-microscopic model has been selected to replace the current phenomenological description of fission barriers. The Finite-Range Liquid-Drop Model (FRLDM) has been implemented in the CONRAD evaluation code and its present implementation shows remarkable consistency with experimental and published benchmark data. The CONRAD code can be used to provide expectation values but also related uncertainties and covariance data. Sensitivity of FRLDM parameters and the correlation matrix between these parameters have been obtained so that further uncertainty propagation on barrier heights can be carried out in the near future.
Highlights
Introduction and motivationsMost of phenomenological models to evaluate fission cross sections rely on the Hill-Wheeler expression for fission transmission coefficient [1]
The phenomenological parameters Vf and ω are respectively associated to the fundamental fission barrier height and curvature
In practice these parameters are adjusted so that evaluator can properly reproduce required observables – usually the fission cross section
Summary
Most of phenomenological models to evaluate fission cross sections rely on the Hill-Wheeler expression for fission transmission coefficient [1]. For a compound nucleus with excitation energy E∗ it reads In this model, the phenomenological parameters Vf and ω are respectively associated to the fundamental fission barrier height and curvature. The phenomenological parameters Vf and ω are respectively associated to the fundamental fission barrier height and curvature In practice these parameters are adjusted so that evaluator can properly reproduce required observables – usually the fission cross section. The macroscopic-microscopic Finite-Range LiquidDrop Model [2] (FRLDM) is a good candidate to achieve this goal as demonstrated by correct nucleus mass predictions, i.e. the binding energy of atomic nuclei As this model can be used to calculate the nucleus energy as it deforms, it can be used to obtain an estimation of fission barrier heights Vf. Best estimate values are not the only required data to perform a proper evaluation. Sensitivity results as well as a correlation matrix are presented
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