Abstract
In 2012 CEA produced a entire new evaluation of sodium nuclear data for the release of the JEFF-3.2 evaluated nuclear data library. During the evaluation process performed with the CONRAD code, several differential measurements (total and discrete inelastic cross-sections) have been used. However double differential data (elastic angular distribution) that were yet available in the EXFOR database were not incorporated in the analysis at that time. The experimental elastic angular distribution were discarded because of it was impossible to obtain a good agreement for both angle-integrated cross-sections and double differential ones. The underlying cause of this disagreement is expected to be due to the attribution of quantum numbers to resonance and related channel amplitudes. Indeed these numbers are imposed during the analysis but impact differently angular distributions and angle-integrated cross-sections. An automated search for an accurate set of quantum numbers has been implemented in order to produce a reliable quantum numbers set. In this paper we present a new evaluation of Na-23 taking into account both differential and double differential measurements. The analysis performed with the CONRAD code reached the level of agreement with experimental data for the total and inelastic cross-sections but this time with a significant improvement for the elastic angular distributions. This new evaluation produced in the ENDF-6 format has then been tested and validated on critical facilities calculation (MASURCA and ZPPR) in different configurations (nominal and voided) in order to assess its performances.
Highlights
In 2012, the nuclear data team at CEA-Cadarache produced an 23Na evaluation for the release of the JEFF3.2 library [1]. This new evaluation was based on several angle-integrated differential experiments, double differential experiments such as Kinneys angular elastic cross-section measurements [2] were not taken into account at that time
We shows that all experimental conditions must be included in the analysis, namely the Doppler-broadening and the resolution function
While working on the Larson data we realized that some small resonances are impacted by the energy resolution and Doppler-broadening. These experimental conditions were not considered in the previous work that led to JEFF3.2
Summary
In 2012, the nuclear data team at CEA-Cadarache produced an 23Na evaluation for the release of the JEFF3.2 library [1]. In the present work we have included the Kinney data and made an automatic 1.5 search for the resonance quantum numbers This procedure improved strongly the agreement with angular distributions (see Fig. 1) while keeping a good agreement with 0.5 integrated data. That we expect a better agreement between experimental data and angular cross section obtained for the new set of resonance parameters, we produced and processed a new ENDF-6 file mostly based on JEFF-3.2 but in which the resonance parameters have been replaced as well as the angular distribution. With our new file the angular distribution exhibit resonant structures consistent with the model used for the modeling of angleintegrated cross sections This consistency was already present in the ENDF/B-VII 23Na evaluation but was one of the defect of the JEFF-3.2 one
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