Study on Geometric Scattering Effects Correction for Precise Estimation of Fast Neutron Shielding in Polyethylene Materials

Fast neutron shielding is a critical component of radiation protection design. Conventional exponential attenuation models based on the narrow-beam (beam approximation) assumption often exhibit large deviations in realistic geometries because they neglect the contribution of scattered neutrons—an effect that becomes particularly prominent for thick hydrogenous shields such as polyethylene. To improve the accuracy of rapid shielding estimates, this study systematically investigates how the “source–shield–detector” geometric configuration influences fast neutron scattering in polyethylene. To overcome the limited adaptability of traditional build-up factor corrections in complex geometries, we propose a physics-informed scattering correction (SC) model. By introducing key geometric parameters—source-to-shield distance, shield thickness, and detector distance—the model dynamically modifies the classical exponential attenuation formulation and analytically integrates the scattered-neutron contribution to the detector flux. Validation against 70 representative geometric configurations simulated with the Monte Carlo code Geant4 shows that the proposed model reduces the mean absolute percentage error (MAPE) from approximately 54% for the exponential attenuation model to approximately 20%, effectively addressing severe flux underestimation in moderately thick shielding cases (5–20 cm). The results provide a practical and reliable tool, as well as a semi-empirical theoretical basis, for fast and accurate engineering estimation of polyethylene-based fast neutron shielding.