An approach for performing resolved and unresolved resonance evaluation based on few or none experimental data available: Application to unstable and short-lived isotopes

Fluctuations in the neutron cross sections resulting from resonance structures have to be accounted for in the calculation of a nuclear system. Regardless of the approach used, deterministic or stochastic, the depression in the neutron flux due to the resonance effects in the cross section must be well understood for the purpose of providing a good understanding of the self-shielding effects and an accurate calculation of any nuclear system. The R-Matrix theory is the mechanism most appropriate to represent the resonance region providing a detailed description of the cross sections thru resonance parameters. The objective of this work is to present an alternative to generate resonance region evaluation on the basis of the R-matrix theory in the resolved and unresolved energy regions. The proposed methodology can be applied to situations where few or none experimental data are available such as the energy dependent neutron cross section. It leverages over the knowledge of information such as thermal cross section values, Westcott factor, resonance integral, coherent and incoherent scattering lengths, scattering radius, and more important, knowledge of average resonance parameters. The approach is demonstrated and validated with applications for an isotope with a well-known resonance evaluation, that is the ¹⁰³Rh, and afterwards to an isotope with minimum experimental data available. The latter is the ¹⁵⁶Eu isotope.