Granularity Level Requirements for Multigroup Evaluated Electron Data Library Use In Boltzmann-Fokker-Planck codes: A Bremsstrahlung Case Study

Abstract

The Generalized Multigroup Theory is applied to the Evaluated Electron Data Library (EEDL) and implemented in the NJOY Nuclear Data Processing System. A demonstration is proposed, asserting that an increased bremsstrahlung (MF=26, MT=527) incidence granularity (G^e) is a deterministic requirement beyond 42MeV. The Perkins-Cullen-Seltzer evaluation work is revisited to increase the EEDL bremsstrahlung granularity level G^e₀ in the current MF=26 gap of 10MeV − 100 GeV. Statistical analyses, including Kolmogorov-Smirnov, Mann-Whitney, and Welch tests, are conducted from Hydrogen to Fermium to assess the quality of the produced data against the EEDL data for the entire photonic spectrum. The ENDF bremsstrahlung flux distribution is validated across the entire periodic table, with the largest discrepancy compared to a reference multigroup solution being under 1.2%. We show that increasing the bremsstrahlung (MF=26, MT=527) data granularity implies (1) an immediate correction of the current high-energy EEDL failure; (2) a dose conformity for 99.18–100% of water voxels with Geant4 between 1MeV and 1 GeV; and (3) a performance gain of 0.33–0.40% compared to the state-of-the-art multigroup CEPXS data from the U.S. Sandia National Laboratories. Perturbations analysis demonstrate that the minimum granularity level required for Boltzmann-Fokker-Planck codes is G^e₈.