279 280 MACROSCOPIC X-RAY FLUORESCENCE CAPABILITY FOR LARGE- SCALE ELEMENTAL MAPPING

Le résumé fourni par la source

Compositional information at moderate resolution over many centimeters will be powerful in materials research, not only to validate casting models but also to understand large-scale phenomena during solidification. These elemental differences across a part have a huge impact on materials properties so that identifying variations will help industry immensely with process optimization and quality control. Therefore, a nondestructive method of obtaining spatially resolved elemental compositions over large areas would be very useful. To this end, we have developed an enhanced macro-x-ray fluorescence (XRF) capability in conjunction with IXRF Systems, Inc. (Houston, Texas) to accommodate samples larger than those that typically fit into an XRF instrument chamber. Our system can accommodate samples up to 70 cm x 70 cm x 25 cm, which is unique in that most systems are trending toward smaller micro- and nano-XRF. This system uses a rhodium tube having a maximum power of 35 kV and 100 �A; the detector is a liquid-nitrogen cooled, lithium-drifted silicon detector, and the smallest spot size is approximately 400 micrometers. Reference standard specimens will enable quantitative elemental mapping and analysis. Challenges to modifying the equipment are described. Nonuniformities in the INCONEL 718 system will be shown and discussed. As another example, segregation of niobium and molybdenum in depleted uranium (DU) castings has been known to occur based on wet chemical analysis [inductively coupled-plasma mass spectrometry (ICP-MS)], but this destructive and time-consuming measurement is not practical for routine inspection of ingots. The U-Nb system is complicated because of overlap of the Nb K-alpha line with the U L-beta. Preliminary quantitative results are included on the distribution of Nb across slices from DU castings with different cooling rates. We foresee this macro-XRF elemental mapping capability becoming a valuable asset to the materials industry.

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