Structural analysis of radiation damage in Precambrian gadolinite from Ytterby by 57Fe Mossbauer spectroscopy, transmission electron microscopy and X-ray diffraction

This paper reports the results of Fe-57 Mossbauer spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and gamma-ray spectroscopy studies of a fully metamict (amorphous) gadolinite sample GYT from Ytterby (Sweden). X-ray and electron diffraction patterns of the sample shows complete lack of long range order (LRO). Nonetheless, Fe-57 Mossbauer spectroscopy of the sample revealed only Fe2+ ions definitely located in octahedral coordinations, similar to the crystalline structure of gadolinite. Radiometric data obtained by gamma-ray spectrometry indicated that the sample remained a closed system for actinides during the entire period since its formation (1.795 x 10(9) years ago). Additionally, geological processes did not change the chemical composition of the sample through such a long time. Consequently, the crystalline structure of fully metamict gadolinite from Ytterby is perfectly restored after high-temperature annealing in argon atmosphere. These and other features result in the conclusion that the gadolinite phase seems to be potential candidate as a nuclear waste form. (C) 2003 Elsevier B.V. All rights reserved.