Updating GEANIE $^{239}$Pu prompt $\gamma$-ray experimental data using modern Hauser-Feshbach fission fragment decay model

Abstract

We calculate fission $\gamma$ rays for neutron-induced reactions on $^{239}$Pu with the Hauser-Feshbach fission fragment decay model. By applying the calculated fission $\gamma$ rays as a background contribution, the historical $^{239}$Pu(n,$x$n$\gamma$) reaction cross section data measured by the GEANIE (GErmanium Array for Neutron Induced Excitations) spectrometer are corrected. The correction also includes other (n,$x$n) reactions that have very similar energies to the $\gamma$ lines reported by GEANIE. In many cases, the original GEANIE data are strongly reduced and they become much closer to the statistical Hauser-Feshbach model predictions. The total inelastic scattering, (n,2n), and (n,3n) cross sections are inferred based on the corrected GEANIE data, and compared with available experimental data as well as the statistical model calculations. Expected $\gamma$-ray energy spectra for neutron-induced measurements on $^{239}$Pu are also discussed.