An improved X-ray technique for scanning the millimeter sized deposits from a multi orifice low pressure impactor

An X-ray spectrometer has been developed in order to study the spot shaped particle deposits from a multi orifice low pressure Berner impactor. The aim of this work was to develop a tool by which elemental mapping of the particle deposits can be made. The analysis is computer controlled so that the concentration for all detected elements can be automatically calculated. The X-ray beam has been strongly collimated and all distances between the sample, the X-ray source and the detector respectively respectively have been minimised. Scanning can be done in both X- and Y-directions in increments of 0.05 mm. For each step an ordinary EDXRF (ED X-ray frequency) spectrum sampled during a live time of 1000 s has been shown to yield much better detection limits than an ordinary analysis. In addition to the use of a small X-ray beam pencil for scanning, the close geometry means improved sensitivities for all elements and especially for the lighter ones like Cl and S. A mapping of each deposit is time consuming and thus may not be the method of choice for routine analyses of multi-orifice impactor samples, but the elemental mapping is seen to be helpful when studying the performance of the impactor. This scanning can also be made regularly to check for changes in the characteristics of the impactor. (Author)