Activation energy of annealed, partially metamict davidite by 57Fe Mössbauer spectroscopy
This study used 57Fe Mössbauer spectroscopy to determine the activation energy for thermal recrystallization of partially metamict davidite [multiple oxide, (La,Ce,Ca,Th)(Y,U)(Ti,Fe3+)20O38]. Radioactive elements in metamict minerals damage crystal structure primarily due to recoil nuclei from α-decay of 238U, 232Th, 235U, and their daughter products. Metamict minerals are widely used in geochronology and can serve as natural analogues for the study of radiation effects in high-level nuclear waste. Analysis was performed on fragments of a davidite sample collected from the Bektau-Ata alkaline granitoid massif (Kazakhstan). Electron-microprobe analysis showed that the sample may be classified as a davidite-(La) due to its La concentration of 3.14 wt. %, relatively low U of 0.88 wt. %, and Th of 0.25 wt. %. The calculated total absorbed α-dose was 8.1 × 1015 α-decay mg-1. The concentration of Fe was 15 wt. % (2.1 % Fe2+ and 12.9 % Fe3+). 57Fe Mössbauer spectroscopy was carried out on fragments of the davidite sample after one-hour annealing under an argon atmosphere from 673 to 1373 K. A Fe2+ component was observed up to 1173 K. Variation in the ratio of amplitudes for the main absorption peaks in the Mössbauer spectra vs. annealing temperature appeared to be a sensitive indicator of thermally-induced recrystallization. The activation energy, EA = 0.45 eV, for recrystallization was determined based on the exponential dependence of the amplitudes’ ratio upon temperature and using an Arrhenius plot.
IF (ISI, 2019): 1.279
5 YEAR IF (ISI, 2019): 1.45
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