Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original paper

Dariusz Malczewski, Agnieszka Grabias, Maria Dziurowicz

Activation energy of annealed, partially metamict davidite by ⁵⁷Fe Mössbauer spectroscopy

Journal of Geosciences, volume 65 (2020), issue 1, 37 - 44

DOI: http://doi.org/10.3190/jgeosci.298

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, E_A = 0.45 eV, for recrystallization was determined based on the exponential dependence of the amplitudes’ ratio upon temperature and using an Arrhenius plot.