Layered structural engineering of Bi₂O₃/PP and WO₃/PP composites for γ-ray shielding in high energy range: anisotropic attenuation mechanisms via Monte Carlo simulation and experiments

The development of non-toxic and flexible polymer-based shielding composites has become a research hotspot due to the severe harm of γ ray to living organisms, mechanical equipment, and environment. However, the γ-ray shielding performance of polymer-based composites in high-energy range remains unsatisfactory. Herein, FLUKA Monte Carlo simulations capable of visualizing γ-photon transport behaviors are investigated in Bi₂O₃/PP and WO₃/PP multi-layer composites with various layered configurations. The simulation results reveal significant anisotropic attenuation effects on shielding characteristics caused by layered configurations and incident path of γ-photons relative to the interface position. Subsequently, single-layer, AB, and sandwich-like ABA composites with a fixed thickness of 2.0 mm are experimentally fabricated via melt-mixing and hot press methods. At 1332 keV, sandwich-like WPPBPPWPP composite (WO₃/PP outer layers + Bi₂O₃/PP core) achieves linear attenuation coefficients and radiation protection efficiency of 0.31 cm⁻¹ and 6 %, respectively, which are 29 % higher than those of single-layer composite. These improvements originate from multiple scattering induced by interlayer interface. Additionally, layered configurations with externally placed high-density fillers (WO₃) and internally placed high atomic number fillers (Bi₂O₃) further promote γ-photon attenuation in high-energy range. Experimental results validate the anisotropic shielding trends observed in MC simulations. Moreover, multi-layer composites demonstrate significantly improved energy storage capacity, thermal stability, and oxidation resistance while maintaining comparable to those of single-layer composites. This work provides a scalable strategy for developing non-toxic and flexible shielding materials applicable in nuclear protection, medical devices, and aerospace systems, where lightweight and efficient radiation attenuation are critical.