A natural polymineral compound in which the major uranium-containing mineral is polycrase (Ti- Ta-niobate) described by the formula АВ2О6 was chosen as a model for studying the behavior of recoil atoms produced by α-decay of actinides. Polycrase, despite its metamict structure, is characterized by the following features distinguishing it from Ti-Ta-niobates of the formula А2В2О7 (pyrochlore and betafite): (1) 1/3 of uranium atoms preserve the initial valence state, U(IV); (2) the U(IV) fraction is characterized by the isotope activity ratio AR(234U/238U) close to that at secular equilibrium; (3) the uranium atoms that underwent oxidation “memorize” their radiogenic origin; as a result, the AR(234U/238U) ratio in the U(VI) fraction is 0.90, and in the most altered part of the mineral it decreases to 0.77; (4) the parent uranium is relatively stable in the metamict structure of polycrase: The half-leaching time for 238U atoms is 2 times longer than that in betafite, zircon, or sphene.

Original languageEnglish
Pages (from-to)79-91
Number of pages13
JournalRadiochemistry
Volume60
Issue number1
DOIs
StatePublished - 1 Jan 2018

    Scopus subject areas

  • Physical and Theoretical Chemistry

    Research areas

  • actinide immobilization, chemical effects of α-decay, incongruent dissolution, metamict minerals, mineral-like HLW matrices, titano-tantalo-niobates, uranium and thorium isotopes, ACID-RESIDUES, HIGH-LEVEL, URANIUM, ALPHA-RECOIL, THORIUM, DECAY, COLORADO CARNOTITE, MONAZITE, chemical effects of alpha-decay, PYROCHLORE, RADIATION-DAMAGE

ID: 28282260