Preliminary study of irradiation effects on thorium phosphate-diphosphate

Thorium phosphate-diphosphate (TPD): Th4(PO4)4P2O7 is proposed as a host matrix for the long-term storage of high level radioactive wastes. Indeed, γ-rays, α and β particles due to the incorporated actinides or fission products will certainly produce several effects, particularly structural and chemical modifications, in the host material. In order to investigate these effects, powdered samples were irradiated with 1.5 Gy dose of γ-rays. The formation of PO32− and POO free radicals was detected using electron spin resonance (ESR) and thermoluminescence (TL) methods. These free radicals do not modify the macroscopic properties of the TPD and disappear when the sample is heated at 400°C. The implantation of He+ ions of 1.6 MeV (fluence: 1016 particles cm−2) and Au3+ ions of 5 MeV (fluence 4×1015 particles cm−2) causes some damages on the surface of sintered samples. Amorphization and chemical decomposition of the matrix were observed for the dose of 1015 particles cm−2 and higher when irradiated with Pb2+ (200 keV) and Au3+ (5 MeV) ion beams. These effects were evidenced by means of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).