Speaker
Description
Fluctuations in neutron-induced reaction cross sections in the unresolved resonance region (URR) influence the self-shielding effect. The self-shielding effect is generally evaluated by using the probability table method. The probability table provides the probability that the total cross section lies within a specified range, together with the corresponding average reaction cross sections. In the conventional approach, the cross sections are calculated by the single-level Breit-Wigner (SLBW) formula, assuming the Wigner distribution for level spacings and the Porter-Thomas distribution for resonance widths. We have developed the GOE-$S$-matrix model, in which the Gaussian orthogonal ensemble (GOE) is directly embedded into the scattering $(S)$ matrix. A key feature of this model is that it does not require the experimentally observed level spacings and resonance widths. Instead, this model uses the transmission coefficients which is used in the Hauser-Feshbach theory. We determine the input transmission coefficients so that the energy-averaged $S$ matrix smoothly connects the resolved resonance region to the higher energy region and calculate cross sections in the URR. We will present the calculated cross sections and the corresponding probability tables for $^{238}$U at 0 K and compare the results with those obtained using the conventional SLBW-based approach.
LA-UR-26-22041
| Session | Evaluation of Nuclear Data (theory, models, codes) |
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