A Comparison of Four Slit Apertures for Selected-Area Analysis with the X-Ray Secondary-Emission Spectrometer

Abstract

AbstractFour types of slit apertures—vertical, horizontal, inclined, and sirtgle-edge—for selected-area analysis with commercial X-ray secondary-emission (fluorescence) spectrometers are described, evaluated, and compared. The vertical and single-edge slits already have been described by the writer and Rizzo. The other two are described here for the first time. The vertical and horizontal slits are secondarybeam apertures; the other two lie in both the primary and secondary beams. AH the slits are mounted on the specimen drawer. No further modification of the spectrometer is required except replacement of the soller collimators with open tunnels or simple slits, and replacement of the flat crystal with a fixed-radius curved crystal to increase sensitivity. The accessories are inexpensive and can be made in even a modest machine shop. They can be installed on or removed from the spectrometer in about 5 min. The accessories are applicable ordy to linear selected areas where composition varies in the direction normal to but not along the line, for example, linear inclusions and sections of plated surfaces, diffusion couples, and interfaces. The four slits were evaluated and compared for resolution, sensitivity, and spectral-line width. Techniques for use, advantages, limitations, and means for improvement are discussed for each of the slits. The horizontal slit is of little value, but each of the others has features which permit analysis of very narrow selected areas for which pinhole apertures would not be sufficiently sensitive. Slit widths as narrow as 0,00012 in. (0.003 mm) have been used in favorable cases. The inclined slit, used with a pulse-height analyzer, is probably the most useful of the four apertures, combining high sensitivity, high resolution, and narrow spectral-line width.