Alpha-recoil damage in natural zirconolite (CaZrTi 2O 7)

Abstract

Radiation effects in natural zirconolites which have received alpha doses from 4.4 × 10 24 alphas/m 3 to greater than 10 26 alphas/m 3 have been studied by transmission electron microscopy. The monoclinic zirconolite crystal structure is retained up to doses of 4.4 × 10 24 alphas/m 3. At intermediate doses ( 3 × 10 25 alphas/m 3), the material consists of a mixture of amorphous and crystalline regions, the latter having an average fcc fluorite structure. At doses greater than 10 26 alphas/m 3 the zirconolite is highly disordered and electron diffraction-amorphous. There is no evidence for remnant long range periodicity, and the broad electron diffraction halos are consistent with scattering from a nonperiodic atomic arrangement. Evidence is presented indicating that the crystallinity reported by others [2] in these high dose zirconolites may be due to alteration, the presence of impurities, or electron beam-heating. All samples with doses greater than 4.4 × 10 24 alphas/m 3 displayed porosity consisting of near-spherical micro-voids. This porosity may be caused by He-bubble formation during U and Th decay.