Photonuclear Physics in Radiation Transport - III: Actinide Cross Sections and Spectra

This paper describes model calculations and nuclear data evaluations of photonuclear reactions on actinides such as ²³⁵U, ²³⁸U, ²³⁷Np, and ²³⁹Pu for incident photon energies from the reaction threshold up to 20 MeV. The calculations are done using the GNASH code, including the giant-dipole resonance for photoabsorption. The emission of secondary particles is computed using a preequilibrium theory, together with an open-ended sequence of the compound nucleus decay using the Hauser-Feschbach theory. The accuracy of the calculated and evaluated cross sections is assessed through extensive comparison with measured cross sections. This work also summarizes evaluation methods used to create actinide photonuclear files for the forthcoming ENDF/B-VII database, which will facilitate radiation transport studies related to photonuclear reactions in a number of technologies including production of photoneutrons and photofission fragments in electron accelerators, shielding studies, and nondestructive detection of nuclear material in particular.