Thermal and gamma-ray-induced density dilution in orthoferrosilite (FeSiO3): implications for photon shielding stability

Abstract

Orthoferrosilite (FeSiO₃), an iron-rich orthopyroxene, was investigated for its structural stability and photon attenuation performance under thermal and gamma-ray environments. This work provides the first quantitative linkage between temperature-dependent polyhedral expansion—specifically the pronounced dilation of FeO₆ octahedra versus rigid SiO₄ tetrahedra—and the resulting degradation in gamma-ray shielding efficiency. Unlike prior studies that treat shielding degradation as a bulk density effect, we establish a crystal-chemical mechanism directly correlating atomic-scale thermal response to macroscopic photon attenuation loss. High-temperature X-ray diffraction analysis revealed a density decrease of approximately 3.2% between 25 °C and 800 °C, driven primarily by the pronounced thermal expansion of FeO₆ octahedra compared to the minimal contraction of SiO₄ tetrahedra. Gamma radiation further reduced density, leading to a LAC by up to 9% at 1 MeV for the highest dose tested. Despite volumetric changes, the effective atomic number (Z_eff ≈ 21.5) and electron density (N_eff ≈ 3.2 × 10²³ e cm⁻³) remained constant, confirming that shielding degradation stems solely from density dilution, not altered interaction probabilities. A key distinction is established: thermally-induced expansion is largely reversible, whereas gamma-induced damage involves athermal defect accumulation with potential irreversibility—a critical insight for predicting long-term shielding performance in mixed-field environments. These results highlight the importance of microstructural stability for orthoferrosilite-based shielding in environments subject to thermal cycling or prolonged irradiation, and suggest pathways for material optimization through compositional tuning and composite design.