Evidence for direct impact damage in metamict titanite CaTiSiO5

Salje, Ekhard K. H. and Dean Taylor, R and Safarik, Douglas J and Lashley, Jason C and Groat, Lee A and Bismayer, Ulli and James Evans, R and Friedman, Richard (2011) Evidence for direct impact damage in metamict titanite CaTiSiO5. Journal of Physics: Condensed Matter, 24 (5). 052202. DOI 10.1088/0953-8984/24/5/052202

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Abstract

We have measured the dose dependence of the degree of amorphization of titanite, CaTiSiO5. Titanite is an often metamict mineral which has been considered as a matrix for the encapsulation of radiogenic waste, such as Pu. The amorphous fraction p of geologically irradiated samples (ages between 0.3 and 1 Ga) follows p = 1 − exp(−BaD) where D is the total dose and the characteristic amorphization mass is Ba = 2.7(3) × 10−19 g. Amorphization follows the direct impact mechanism where each α-decay leads to a recoil of the radiogenic atoms (mostly Th and U), which then, in turn, displaces some 5000 atoms of the titanite matrix. The amorphization behaviour is almost identical with that of zircon, ZrSiO4, which has a similar molecular mass. While the recrystallization mechanism and elastic behaviour of the two minerals are very different, we do not find significant differences for the amorphization mechanism. Our samples have undergone little reheating over their geological history, since heating over 800 K would lead to rapid recrystallization for which we have found no evidence.

Item Type: Article
Uncontrolled Keywords: 2011AREP; IA63;
Subjects: 03 - Mineral Sciences
Divisions: 03 - Mineral Sciences
Journal or Publication Title: Journal of Physics: Condensed Matter
Volume: 24
Page Range: 052202
Identification Number: 10.1088/0953-8984/24/5/052202
Depositing User: Sarah Humbert
Date Deposited: 25 Feb 2012 12:15
Last Modified: 23 Jul 2013 10:03
URI: http://eprints.esc.cam.ac.uk/id/eprint/2393

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