Velma M Montoya

F-37 Macroscopic X-ray Fluorescence Capability for Large-Scale Elemental Mapping

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 microand 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 (ICPMS)], 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. INTRODUCTION The ability to map compositional information over large distances (tens of centimeters) can be used in many applications. Routine and straightforward measurements of large-scale macrosegregation will have innumerable benefits to the metallurgical community and address a critical barrier to progress. Instead of an assumed ideal uniform average composition, in reality elemental distributions often form across a specimen during cooling that can cause an undesirable final microstructure, leading to unwanted materials properties in the final product and causing part failure. Measuring the existence of compositional inhomogeneities, as well as the conditions under which they form, are key components of process optimization; this paper describes our preliminary efforts to integrate macroscopic x-ray fluorescence (macro-XRF) measurements with our foundry for optimization of casting processes. More importantly, understanding the underlying scientific phenomena allows growth of casting technology beyond trial-and-error experimental work toward modeling and predictive capability. In the long-term, more advanced casting codes could be developed as existing theoretical models mature through validation [Flemings (1974); Mehrabian et al. (1970)]. 279 80

Light yield measurements of milled BaFCl:Eu inorganic crystals

In recent years, composite scintillators consisting of nanosize inorganic crystals in an organic matrix have been actively developed. Ideally these scintillators would have efficiency and resolution similar to inorganic crystals, but at the same time would be inexpensive and easy to manufacture. In order to make composite scintillators optically transparent, McKigney et al. finds that nanosize inorganic crystals should be used in order to reduce optical scattering. One way to produce these nanosize inorganic crystals is through wet milling, where inorganic crystals are ground with microsize beads in an organic solvent to achieve size reduction. Milling is relatively simple in terms of preparation and equipment; however, milling is also known to introduce defects into the ground material. Therefore, a new light yield measurement technique is developed to evaluate the degree to which milling alters the light yield of the milled inorganic crystals. In this work, the light yield measurement technique is applied to samples containing BaFCl:Eu inorganic crystals milled in a tributyl phosphate (TBP) and cyclohexane mixture.