Uranium-bearing francolites present in organic-rich limestones of NW Greece: a preliminary study using synchrotron radiation and fission track techniques

Synchrotron radiation techniques (μ-XRF and μ-XANES) were applied to the study of organic-rich phosphatized limestones of NW Greece (Epirus). The results revealed uranium accumulation in areas of the material containing, among others, carbonate apatite (francolite) and organic matter. The UL ₃-edge of μ-XANES spectra showed that uranium was present in tetravalent form. U-bearing francolite crystals were separated from the rock and characterized by Raman spectroscopy and microprobe. The analysis of the crystals also indicated the presence of sodium and sulfur. The uranium presence in the crystals was also visualized, after neutron irradiation and etching, by the observation of the fission tracks.

     

Isotopic analysis for degradation diagnosis of calcite matrix in mortar

Mortar that was used in building as well as in conservation and restoration works of wall paintings have been analysed isotopically (δ¹³C and δ¹⁸O) in order to evaluate the setting environments and secondary processes, to distinguish the structural components used and to determine the exact causes that incurred the degradation phenomena. The material undergoes weathering and decay on a large proportion of its surface and in depth, due to the infiltration of water through the structural blocks. Mineralogical analysis indicated signs of sulphation and dissolution/recrystallisation processes taking place on the material, whereas stable isotopes provided information relative to the origin of the CO₂ and water during calcite formation and degradation processes. Isotopic change of the initial δ¹³C and δ¹⁸O in carbonate matrix was caused by alteration of the primary source of CO₂ and H₂O in mortar over time, particularly by recrystallisation of calcite with porewater, evaporated or re-condensed water, and CO₂ from various sources of atmospheric and biogenic origin. Human influence (surface treatment) and biological growth (e.g. fungus) are major exogenic processes which may alter δ¹⁸O and δ¹³C in lime mortar.