Fixed-Angle Reflectance from Uranium Compounds and U-Bearing Minerals: Experimental Challenges to Determine the Optical Constants n and k

Conference · Fri May 17 04:00:00 EDT 2019

DOI:https://doi.org/10.1117/12.2519504· OSTI ID:1591629

Devetter, Brent M. ^[1]; Resch, Charles T. ^[2]; Myers, Tanya L. ^[2]; Corbey, Jordan F. ^[2]; Kelly-Gorham, Molly Rose K. ^[2]; Cannon, Bret D. ^[2]; Scharko, Nicole K. ^[2]; Johnson, Timothy J. ^[2]

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1. University of Colorado at Boulder
2. BATTELLE (PACIFIC NW LAB)

Fixed-angle reflectance spectroscopy using a commercial Fourier transform infrared (FTIR) spectrometer was employed to derive the optical constants n and k of several uranium compounds. This technique relies upon measurement of the quantitative reflectance R(?) spectra from a polished surface across a broad spectral range (in this case, the mid- and far-IR covering ca. 7500 to 50 cm-1) followed by application of the Kramers-Kronig transformation (KKT). Near-normal fixed-angle measurements as used in this technique require continuous reflectance spectra to as low a wavenumber value as possible. Here, we discuss some of the many challenges in measuring the far-IR and very far-IR (terahertz) spectra using an interferometric instrument, particularly those stemming from small sample sizes, typically just millimeters on a face for crystalline samples, as well as limitations due to optical components and diffraction. We apply this method to single-crystal UO2 and its mineralogical form uraninite, as well as other U-bearing minerals such as autunite [Ca(UO2)2(PO4)2·8-12H2O] and the dehydrated form of autunite, meta-autunite. In addition to the specular reflectance spectra, x-ray diffractometry was used as a confirmatory technique to analyze the surface composition of the species. Deriving the infrared optical constants for such U-bearing species (as well as other solids) will enable nondestructive detection under a variety of environmental and compositional conditions.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1591629
• Report Number(s): PNNL-SA-143056
• Country of Publication: United States
• Language: English

Related Subjects

Uranium Minerals
infrared spectroscopy
optical constants
Kramers-Kronig transformation
far-infrared