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Validation of the Characteristic Function Model for the Unresolved Resonance Region

N. Koyumdjieva, N. Janeva, K. Volev

Nuclear Science and Engineering

Volume 137 / Number 2 / February 2001 / Pages 194-205


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There is a significant extension of the region of resolved resonances (RRR) for some nuclei to higher energies, and this has repercussions on the last updated versions of the evaluated nuclear data libraries. This energy extension covers intervals of the resonant cross-section structure, previously treated as an unresolved resonance region (URR). The reality of this situation provides an opportunity to verify a new statistical model of the resonant cross-section structure in the URR based on the characteristic function F of the R-matrix element distribution. For this purpose, the average cross sections and self-shielding factors obtained by the characteristic function model are compared with the corresponding quantities calculated by the Reich-Moore formalism of the R-matrix theory of nuclear reactions with the evaluated resonance parameters in the RRR. The ENDF/B-VI and JENDL 3.2 resolved resonance parameters of 56Fe and 238U are used for the cross-section calculations.

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