Application of analytical electron microscopy to the study of radiation damage in natural zirconolite

An AEM ratio technique for the analysis of 25 elements in finely zoned natural zirconolite was used in conjunction with electron diffraction and imaging techniques to examine the effects of alpha-decay damage on zirconolites from Bergell, Switzerland-Italy and Adamello, northern Italy. Comparison of AEM and EPMA results confirms that the AFM technique can be used to obtain accurate information on the chemical formula of zirconolite. The TEM images and diffraction patterns in this study are analogous to those of previous authors. They support the proposition that radiation damage ingrowth can be adequately described by the accumulation and overlap of isolated alpha-recoil collision cascades, producing progressively larger amorphous domains. Careful determination of Th and U contents by AEM gives an accurate indication of the dose range of the crystalline-amorphous transformation. For the samples from Bergell and Adamello, the transformation occurs over a dose range of 0.05 × 1016 to just over 1 × 1016a/mg, consistent with studies of synthetic zirconolite doped with 238Pu or 244Cm. The Bergell zirconolites all exhibited diffraction patterns characteristic of the zirconolite-2M. Those grains containing REE and Th+U contents up to ≈0.1 and ≈0.03 atoms per formula unit, respectively, exhibit a high level of crystallographic perfection. While those grains containing ≈0.2 REE and 0.06 Th+U atoms per formula unit, exhibit twinning and stacking disorder.