Britholite, ideally Ca4-xREE6+x(SiO4) 6O2 (REE=rare earth elements), has the hexagonal structure of apatite, a candidate waste form for actinides. Two synthetic britholites: Ca3.05Ce2.38Fe0.25Gd 5.37Si4.88O26 (N56) and Ca 3.78La0.95Ce1.45Zr0.78Fe 0.14Nd2.15Eu0.50Si6.02O 26 (N88) (P63; Z=1) were irradiated with 1.0 MeV Kr2+ and 1.5 MeV Xe+ over the temperature range of 50-973 K. The process of ion irradiation-induced amorphization, including the effects of the target mass and the ion mass, and the recrystallization of amorphous domains due to ionizing irradiation were investigated. The critical amorphization temperature, Tc was determined to be 910 K for N56 (1.0 MeV Kr2+), 880 K for N88 (1.0 MeV Kr2+) and 1010 K for N88 (1.5 MeV Xe+). The sequence of increasing Tc correlates with the mass of the incident ion; whereas, the ratio of electronic to nuclear stopping power (ENSP) is inversely correlated with Tc. Electron irradiations were conducted on previously amorphized britholite (N56) with an electron flux of 1.07 × 1025 e-/m2/s. The ionizing radiation resulted in recrystallization at the absorbed dose of 6.2 × 1013 Gy. This result suggests that the ionizing radiation can induce recrystallization in silicate apatites, similar to that observed for phosphate apatite.
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