Effect of 10 MeV electron irradiation on hydroxyapatite (HAP)

To understand the impact of radiation doses, polycrystalline hydroxyapatite (HAP) samples were exposed to 10 MeV electron irradiation, reaching doses of up to 20 MGy and their structural–thermal–optical properties were compared with unirradiated sample by using powder X–ray diffraction (XRD), energy-dispersive X–ray fluorescence (EDXRF), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and photoluminescence (PL) measurements. The results suggest that the samples exhibit high-phase stability, though irradiation induces the formation of surface defects and oxygen vacancies, while leaving morphology unchanged. It was noted that the lattice contracts, leading to reduced bond lengths and an increase in bond covalency, consequently resulting in a decrease in charge transfer (CT) energy. This nephelauxetic (covalency) effect is associated with a red shift observed in the excitation spectrum. Additionally, a noticeable enhancement of luminescence intensity was exhibited by HAP-1MGy sample attribute to the structured alignment of defects and oxygen vacancies within the lattice. These findings imply the exceptional radiation durability of HAP even after exposure to high electron-irradiation doses.