$R$-matrix analysis and prediction of low-energy neutron-induced fission cross sections for a range of Pu isotopes

$R$ -matrix analysis and prediction of low-energy neutron-induced fission cross sections for a range of Pu isotopes

O. Bouland, J. E. Lynn, and P. Talou

Phys. Rev. C 88, 054612 – Published 18 November 2013; Erratum Phys. Rev. C 101, 039901 (2020)

Abstract

Neutron-induced fission cross sections for the plutonium isotopes from 236 to 244 are computed for neutrons of a few keV up to 5.5 MeV incident energy, using the Hauser-Feshbach statistical theory of nuclear reactions, modified to treat the fission decay channel in the $R$ -matrix formalism. The fluctuations of the fission decay widths owing to the presence of intermediate structures in the second well and to the coupling of class I and class II states are simulated by Monte Carlo sampling of the underlying model parameter distributions. The accuracy of this approach is tested relative to the results of well-known analytical formulations for the average fission cross sections. Special attention is paid to the choice and consistency of the model input parameters, in part obtained from microscopic nuclear structure calculations. The predictive capabilities offered by our method are tested against the neutron-induced fission of the very short-lived $^{243}$ Pu ( $τ_{1 / 2} = 4.95$ h) for which no measurement exist. Our calculations, consistent over all the Pu isotope series, demonstrate that $^{243}$ Pu is fissile, in contrast to what is reported in the standard ENDF/B-VII.1 and JEFF-3.1.2 evaluated libraries. No recommendations are made in the JENDL-4.0 data library for this isotope.