57Fe Mossbauer study of one-hour annealing in argon of radiation damage in metamict gadolinite from Ytterby

Gadolinite, REE2FeBe2Si2O10, belongs to the group of metamict minerals. Metamict minerals incorporate uranium and thorium in their structures. Alpha-decays of uranium and thorium series inside the gadolinite structure cause radiation damage of the crystalline lattice and can produce complete metamictization (amorphization) of the crystal. The original structure of metamict minerals can be restored by heating. This paper presents Fe-57 Mossbauer studies of fully metamict gadolinite from Ytterby (Sweden) after a one-hour annealing process in argon atmosphere at high temperatures. Changes in the Mossbauer parameters are sensitive indicators of the thermal recrystallization process and revealed two stages of the structural recovery. The first stage from 873 to 1073 K and the second one from 1133 to 1473 K. These observations are confirmed by X-ray diffraction.