Incompatible Gamma Emission between GEANT4 Thermal Neutron Capture Simulations and ENDF Data

GEANT4 is a software toolkit that uses Monte Carlo methods to simulate how particles travel through matter. One of its applications is to model neutron capture reactions and subsequent gamma-rays. These gamma ray emissions create a unique spectrum for every isotope that can be used to identify material composition and are important for space exploration, oil well logging, nuclear forensics, and non-proliferation. GEANT4 uses data from the Evaluated Nuclear Data File (ENDF/B), and we performed thermal neutron capture simulations for various isotopes in order to compare their spectra. This work, performed at the National Nuclear Data Center (NNDC), demonstrates discrepancies between gammas produced by GEANT4 and those of ENDF. We have also explored different combinations of input flags, which modify how GEANT4 models capture gamma-ray emissions, and their effect on the spectra of several target isotopes was investigated. With these assessments of GEANT4's quality, we point to alternatives that would better determine gamma ray emissions from a given cascade based on emission probabilities per energy level. If implemented, these alternatives would allow for a more accurate simulation of neutron capture reactions in a variety of experiments.