Speaker
Description
X-Ray Fluorescence with sufficient spatial resolution is an efficient non-destructive tool for mapping the distribution of several elements in dendrochronological samples as a probe into uptake of these elements during the tree growth. Here we present an example of secondary penetration of metals, arsenic and sulfur into wood from archaeological findings south of the town Havlíčkův Brod. Fir wood was used in a construction for crushing of polymetallic ores and slags from a nearby smelter. Several trunk fragments were dendrochronologically dated to 13th century when intense mining and smelting in the region begun.
A trial scan of a tangential section with rough surface indicated a significant contamination with Zn, Pb and Fe. A cross-section of a trunk with smooth surface was scanned in two profiles and one 2D-map with lateral resolution of 50 µm, and the scattering of the primary radiation was used as a proxy of wood density. In addition, relatively large spots were measured in the section and in bark with a portable XRF analyzer. Mechanical contamination by soil particles enhanced the concentrations of most of the elements in the bark or close to it.
Distribution of some elements (Zn, Pb, S, Fe, As, and Cu at least) indicates their significant transport in solution. The domains most enriched in such contaminants show dark staining. Elements from the external contamination mainly penetrated into wide, more porous rings in outer part of the trunk, but in detail, they reach peak concentrations in latewood rings (which overlap with local density maxima).
The slightly higher content of Mn and lower content of K and S in the oldest, relatively dense rings may represent the original growth zoning. Partly preserved but more complicated primary distribution is also probable for Ca. Possible presence of original seasonal pattern of some elements is discussed.