Fixed-angle reflectance from uranium compounds and U-bearing minerals: experimental challenges to determine the optical constants n and k
Abstract
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(ν) 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 Ubearing 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.
- Publication:
-
Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XX
- Pub Date:
- May 2019
- DOI:
- 10.1117/12.2519504
- Bibcode:
- 2019SPIE11010E..0SD