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Matco Associates Inc. Specialists in Materials Engineering, Corrosion and Failure Analysis

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The Failure Analysis Forum: Powder x-ray diffraction radiation damage puzzle

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    • CommentAuthordongibbon
    • CommentTimeFeb 27th 2007
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    There is a great deal of published information on beam damage from synchrotron-generated x-radiation, but little on other than saftey-related issues for "normal" diffiractometers operating in the 40 Kv range. We tested our Siemens D-500 diffractometer using a wide variety of materials for sample holders in an attampt to reduce background scattering in the 10 to 35 degree two-theta range. One of the best means of doing this is a "low-background plate" specially made by Gem Dugout in State College, PA, using a synthetic quartz crystal cut and polished to create a surface several degrees off of perpendicular to the c-axis. This does indeed produce a background about one quarter of the intensity of that from a glass slide... but not zero by any means. We still haven't solved that puzzle completely and any suggestions for improving the situation would be appreciated.

    However, we have generated another puzzle: when we run powder samples on ordinary glass slides the beam produces a brown patch of radiation damage in the glass, most intense in the center and spreading out to nothing over about a half-inche wide strip, a perfect map of the beam intenstiy distribution in the glass. The diffractometer is running with 1 degree slits and a graphite monochromator (the latter having no effect on the beam-sample interaction, of course). What is happening physically in the glass to produce the color change? It can't be like color centers in crystalline material... so what is it?

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