Published online by Cambridge University Press: 03 September 2012
The aeschynite structure-type (Ce,Nd,La,Th,U,Ca)(Nb,Ti)2O6, and the rare-earthsilicate apatite structure-type with the formula (Ce,La,Nd,Ca,Th)10(SiO4,PO4)6(O,F,OH)2are important rare-earth and actinide host phases for high-level nuclearwaste. Natural phases of these structure-types have calculated alpha-decaydoses up to ∼1017 α-events/mg which have accumulated overhundreds of millions of years. Transmission electron microscopy has beenused to study the microstructure of α-decay damage in aeschynite andbritholite. Electron diffraction analysis of natural aeschynite revealedthat minerals originally crystalline gradually lost their crystallinity withincreasing alpha-decay doses. Helium bubbles were found in the aeschynitewhich have accumulated up to ∼2×1016 α-events/mg. These bubblesmay nucleate within collision cascades during a-decay damage. Electronirradiation has an enhanced rare-gas migration and the formation of largerbubbles. High-resolution electron microscopy (HRTEM) revealed thatamorphization during accumulation of a-decay damage was from alpha-recoilnuclei collision cascades, in both the aeschynite and britholite.