Joseph R. Swider Surface and Microanalysis Science Division Chemical Science and Technology Laboratory
Although many techniques for microanalysis exist, few are totally nondestructive, easy to maintain, or portable. Techniques such as Electron Probe Microanalysis (EPMA) deliver sub-micrometer beams, but are destructive in sample preparation and in analysis, costly, and not portable. In order to create a microanalysis instrument that has low detection limits and is also flexible and portable, we have utilized the benefits of X-ray Fluorescence (XRF) with a capillary focusing optic. Of the many methods used for X-ray focusing, capillary optics best suits a micro-XRF instrument: the devices are compact, easy to implement, focus a divergent beam, and conserve the beam brilliance. The optic is positioned in x,y,z, pitch, and yaw directions to maximize X-ray capture and transmission. The focused beam location and attributes are determined with an X-ray imager. Samples replace the imager at the focal distance and fluorescent radiation is detected with a Si(Li) detector. Motion control, data acquisition, and image acquisition and processing are accomplished on a single PC. Our capillary micro-XRF instrument has successfully analyzed spherical particles down to 10 micrometer diameter. Detection is in the range of 0.1 ng for elements in silicate glasses excited with W tube radiation. The instrument is easily manipulated to accommodate samples in a variety of shapes and sizes and to analyze samples in situ.