ABSTRACTThe aeschynite structure-type
(Ce,Nd,La,Th,U,Ca)(Nb,Ti)2O6, and the rare-earth
silicate apatite structure-type with the formula
(Ce,La,Nd,Ca,Th)10(SiO4,PO4)6(O,F,OH)2
are important rare-earth and actinide host phases for high-level nuclear
waste. Natural phases of these structure-types have calculated alpha-decay
doses up to ∼1017 α-events/mg which have accumulated over
hundreds of millions of years. Transmission electron microscopy has been
used to study the microstructure of α-decay damage in aeschynite and
britholite. Electron diffraction analysis of natural aeschynite revealed
that minerals originally crystalline gradually lost their crystallinity with
increasing alpha-decay doses. Helium bubbles were found in the aeschynite
which have accumulated up to ∼2×1016 α-events/mg. These bubbles
may nucleate within collision cascades during a-decay damage. Electron
irradiation has an enhanced rare-gas migration and the formation of larger
bubbles. High-resolution electron microscopy (HRTEM) revealed that
amorphization during accumulation of a-decay damage was from alpha-recoil
nuclei collision cascades, in both the aeschynite and britholite.
Transmission Electron Microscopy Study on the Grain Boundaries and Magnetic Domains in Nd–Fe–B Based Magnets