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The crystalline-amorphous transformation in natural zirconolite: evidence for long-term annealing

Authors: 
Lumpkin G.R., Smith K.L., Blackford M.G., Gieré R., Williams C.T.
Year: 
1 998
Source: 
Materials Research Society, Symposium Proceedings
Abstract: 
Dose-age relationships have been determined by analytical and transmission electron microscopy (AEM and TEM) for the onset dose and critical amorphization dose of a suite of natural zirconolites. Together with a preliminary investigation of the thermal histories of the zirconolite-bearing rocks, the results indicate that valid estimates of D0 (intercept dose at t = 0) and K (annealing rate constant) are obtained and that the host rocks experienced temperatures on the order of 100-200 °C averaged over time. The natural samples are therefore best suited as radiation damage analogues for waste forms stored under deep borehole conditions where temperatures of 100-450 °C are expected. Our results indicate that the critical amorphization (or saturation) dose of zirconolite will increase by a factor of approximately 2 or more as a result of storage at elevated temperature. The effect of long-term annealing on the critical amorphization dose is only important for times in excess of 107-108 years due to the low annealing rate constant of 10−9/yr.
EES Authors: 
Reto Gieré

Department of Earth and Environmental Science / University of Pennsylvania, 251 Hayden Hall, 240 South 33rd Street, Philadelphia, PA 19104-6316