An ESR study of defects in irradiated hydroxyapatite

Radiation-induced defects in synthetic hydroxyapatite (HAp) of six different origins have been investigated by electron spin resonance (ESR), X-ray diffraction (XRD), Raman scattering and IR measurements. The orthorhombic CO2− radicals were detected in almost of all the samples examined, but the isotropic CO2− was produced only in water-containing HAp with low crystallinity. The doublet signal due to H0 was clearly detected in HAp with extreme calcium deficiency as compared to the stoichiometry. The results of ESR and FTIR suggest that water molecules in low crystalline HAp are not on the surface but embedded in the HAp crystalline lattice.