Partial γ-Ray cross sections for the reaction ²³⁹Pu(n, 2nγ_i) and the ²³⁹Pu(n, 2n) cross section

Absolute partial γ-ray cross sections for discrete γ-ray production in the ²³⁹Pu(n, 2nγ_i)²³⁸Pu reaction have been measured. The experiments were performed at LANSCE/WNR on the 60R neutron flight path. Reaction γ-rays were measured using the large-scale Compton-suppressed array of Ge detectors, GEANIE. The motivation for this experiment, an overview of the partial γ-ray cross-section measurement, and an introduction to the main experimental issues will be presented. The energy resolution of the Ge detectors allowed identification of reaction γ rays above the background of sample radioactivity and fission γ rays. The use of planar Ge detectors with their reduced sensitivity to neutron interactions and improved line shape was also important to the success of this experiment. Absolute partial γ-ray cross sections are presented for the 6₁⁺ → 4₁⁺ member of the ground state rotational band in ²³⁸Pu, together with miscellaneous other γ-ray partial cross sections. The n, 2n reaction cross section shape and magnitude as a function of neutron energy were extracted from these partial cross sections using nuclear modeling (enhanced Hauser-Feshbach) to relate partial γ-ray cross sections to the n, 2n cross section. The critical nuclear modeling issue is the ratio of a partial cross section to the reaction channel cross section, and not the prediction of the absolute magnitude.