Non- identical thermochemical behavior of 234U-and 238U- isotopes in metamict britholite.

A radiochemical analysis of the valence state of uranium isotopes in minerals involves isolation of the U(IV) and U(VI) valence forms and determination of the radioactivity of the 234 U and 238 U isotopes in each fraction. If the nuclear decay of the uranium in the minerals is accompanied by a redox process, the distribution of the 234 U isotope in the U(IV) and U(VI) forms will differ from that of the 238 U isotope: oxidation leads to enrichment of the U(VI) fraction with the radiogenic 234 U isotope; reduction facilitates enrichment of the U(IV) fraction with 234 U. If the mineral is heated to 600–700 °C before the radiochemical analysis, then an equilibrium activity ratio (AR) for both valences. The question arises: What are the processes that bring this about? The authors of this research studied changes of the AR in the U(IV) and U(VI) fractions after isochronous thermal annealing. [ABSTRACT FROM AUTHOR]