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

[摘要] This study used 57Fe Mössbauer spectroscopy to determine the activation energy for thermal recrystallization of partiallymetamict davidite [multiple oxide, (La,Ce,Ca,Th)(Y,U)(Ti,Fe3+)20O38]. Radioactive elements in metamict minerals damagecrystal structure primarily due to recoil nuclei from α-decay of 238U, 232Th, 235U, and their daughter products. Metamictminerals are widely used in geochronology and can serve as natural analogues for the study of radiation effects in highlevel nuclear waste. Analysis was performed on fragments of a davidite sample collected from the Bektau-Ata alkalinegranitoid 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 totalabsorbed α-dose was 8.1×1015 α-decay mg–1. The concentration of Fe was 15 wt. % (2.1 % Fe2+ and 12.9 % Fe3+). 57FeMössbauer spectroscopy was carried out on fragments of the davidite sample after one-hour annealing under an argonatmosphere from 673 to 1373 K. A Fe2+ component was observed up to 1173 K. Variation in the ratio of amplitudes forthe main absorption peaks in the Mössbauer spectra vs. annealing temperature appeared to be a sensitive indicator ofthermally-induced recrystallization. The activation energy, EA = 0.45 eV, for recrystallization was determined based onthe exponential dependence of the amplitudes’ ratio upon temperature and using an Arrhenius plot.

[学科分类] 自动化工程

[关键词] partially metamict davidite;activation energy;Mössbauer spectroscopy;annealing