An EDXRF system for scanning samples in steps of 5 pm was developed. The system is based on a conventional x-ray tube and secondary target in closest possible geometry. For tree ring analysis, which was made in steps of 200 pm, the exciting x-ray beam was allowed to pass through a slit collimator of dimensions 0.1 x 1 mm made of pure silver. The sample holder is movable in steps of 5 pm in three orthogonal directions. The beam path of the exciting and fluorescent radiation can be adjusted in relation to the sample plane by the movable sample holder. Further adjustments can be made by a movable detector platform. All movements are driven by microcomputercontrolled step motors. The detection limits of thick samples, like tree biopsies, are of the order of parts per million for medium-heavy elements. The system was applied to multielement analysis of healthy samples of pine, birch and spruce biopsies. Long-term trends in some trace element concentrations could be seen in these samples, together with the possible influence of stress.

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