Effects of dose rate and temperature on the crystalline-to-metamict transformation in the ABO (sub 4) orthosilicates

Radiation damage effects in naturally irradiated zircon and thorite were compared with those seen in ion-beam-irradiated (800 keV Kr (super +) ) synthetic specimens of zircon, hafnon, thorite, huttonite and crystalline thorite from Kipawa. All the specimens became amorphous at < 1 dpa at < 600 degrees C; at higher T, the amorphization dose increases in the order: Kipawa thorite, synthetic thorite, hafnon, zircon, huttonite. Two stages of amorphization were identified, with activation energies of approximately 1.0 eV and 3.1-3.7 eV. Whereas natural zircon and thorite undergo radiation-induced amorphization in general similar to that produced by ion bombardment, the amorphization dose is significantly higher due to the long-term annealing effects. Thorite is predicted to become metamict after relatively short times, whereas huttonite recovers more rapidly from the effects of irradiation and takes longer to become metamict.