Induced swelling in radiation-damaged ZrSiO4

Samples containing 10 wt % 238Pu incurred bulk radiation damage through internal alpha-decay processes. Undoped samples were subjected to external irradiation from 5.5-MeV alpha sources, and from a 60Co gamma source. Actinide-doped ZrSiO4 exhibits dose-dependent swelling caused by displacement processes leading to ingrowth of amorphous regions. Bulk-density and XRD measurements as a function of dose showed first-order exponential ingrowth behavior similar to that observed in other actinide-doped materials. Results are compared with reported data for naturally damaged crystals subjected to significantly lower alpha-decay rates. No significant dose-rate dependence on damage ingrowth has been observed. Kinetic models for the observed dose-dependent swelling are proposed and rate constants for damage ingrowth in synthetic and natural crystals are compared. Vibrational Raman measurements indicate that the initial stage of damage ingrowth is confined to the silicate sublattice. Vibrational results are discussed in terms of microstructural changes which result from irradiation