Photonuclear Neutron Production in OpenMC: Verification Against MCNPX, FLUKA, and a First-Collision Analytical Solution
Abstract
The modelling of photonuclear reactions is increasingly important for applications involving high-energy photon fields, including accelerator-driven neutron sources, radiation shielding, medical physics, and fusion technologies. OpenMC photonuclear physics is currently available only in an unofficial development branch and requires independent verification before broader scientific use. This work verifies the OpenMC photonuclear implementation using six single-collision broomstick numerical benchmarks with 2H, 9Be, and 238U targets, irradiated by monoenergetic 5 MeV and 15 MeV photons and by a continuous 1-20 MeV LINAC-representative spectrum. OpenMC was compared with MCNPX under common ENDF7u photonuclear data, with FLUKA as an independent native-model reference, and with a first-collision analytical solution based on ENDF7u; calculations with the IAEA/PD-2019 library quantified nuclear-data sensitivity. Energy-resolved, angular, and integrated photoneutron yields were compared. Under common ENDF7u data, OpenMC and MCNPX agreed to within a few tenths of a percent in integrated yield, consistent with the statistical uncertainty, and their energy and angular distributions agreed closely, apart from small kinematic differences in the light-nuclide cases. Replacing ENDF7u with IAEA/PD-2019 produced deviations of up to 13.9%, largest for continuous-source 9Be and monoenergetic 2H (11.3%). FLUKA differed from OpenMC-ENDF7u by up to 9% (monoenergetic) and 2.5% (continuous source) and predicted a markedly different angular distribution for 2H. These results verify that the OpenMC photonuclear implementation reliably reproduces MCNPX under a given nuclear-data evaluation, while no single library or model is uniformly preferable from the present comparisons alone.
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BibTeX
@misc{loi2026photonuclear,
title = {{Photonuclear Neutron Production in OpenMC: Verification Against MCNPX, FLUKA, and a First-Collision Analytical Solution}},
author = {Lorenzo Loi and Andrea Missaglia and Guy Stein and Carolina Introini and David Breitenmoser and Shaun D. Clarke and Sara A. Pozzi and Antonio Cammi},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2607.26045},
eprint = {2607.26045},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.26045},
}
RIS
TY - UNPB
TI - Photonuclear Neutron Production in OpenMC: Verification Against MCNPX, FLUKA, and a First-Collision Analytical Solution
AU - Lorenzo Loi
AU - Andrea Missaglia
AU - Guy Stein
AU - Carolina Introini
AU - David Breitenmoser
AU - Shaun D. Clarke
AU - Sara A. Pozzi
AU - Antonio Cammi
PY - 2026
DA - 2026/10/29
PB - arXiv
DO - 10.48550/arxiv.2607.26045
UR - https://arxiv.org/abs/2607.26045
AB - The modelling of photonuclear reactions is increasingly important for applications involving high-energy photon fields, including accelerator-driven neutron sources, radiation shielding, medical physics, and fusion technologies. OpenMC photonuclear physics is currently available only in an unofficial development branch and requires independent verification before broader scientific use. This work verifies the OpenMC photonuclear implementation using six single-collision broomstick numerical benchmarks with 2H, 9Be, and 238U targets, irradiated by monoenergetic 5 MeV and 15 MeV photons and by a continuous 1-20 MeV LINAC-representative spectrum. OpenMC was compared with MCNPX under common ENDF7u photonuclear data, with FLUKA as an independent native-model reference, and with a first-collision analytical solution based on ENDF7u; calculations with the IAEA/PD-2019 library quantified nuclear-data sensitivity. Energy-resolved, angular, and integrated photoneutron yields were compared. Under common ENDF7u data, OpenMC and MCNPX agreed to within a few tenths of a percent in integrated yield, consistent with the statistical uncertainty, and their energy and angular distributions agreed closely, apart from small kinematic differences in the light-nuclide cases. Replacing ENDF7u with IAEA/PD-2019 produced deviations of up to 13.9%, largest for continuous-source 9Be and monoenergetic 2H (11.3%). FLUKA differed from OpenMC-ENDF7u by up to 9% (monoenergetic) and 2.5% (continuous source) and predicted a markedly different angular distribution for 2H. These results verify that the OpenMC photonuclear implementation reliably reproduces MCNPX under a given nuclear-data evaluation, while no single library or model is uniformly preferable from the present comparisons alone.
ER -