Year
2010
Abstract
In July 2009, the authors published experimental results from a benchtop x-ray optical instrument that is capable of measuring curium concentrations as low as 0.3 parts per million in dried 1-microliter droplets of solution. This Monochromatic Wavelength-Dispersive X-Ray Fluorescence (MWDXRF) system was designed, built, and tested in collaboration with X-Ray Optical Systems, Inc. of East Greenbush, New York. The “single-channel” Cm MWDXRF system tested in 2009 was optimized to collect 14.96-keV curium L-alpha-1 x-rays (or 14.96-keV yttrium K-alpha-1 x-rays) that result from interrogating a specimen with a 20.2-keV x-ray beam. A new “dual-channel” uranium-thorium MWDXRF system is under development in 2010. The U-Th MWDXRF system will have two collection channels: one for the uranium L-alpha-1 x-ray (13.62 keV), and one for the thorium L-alpha-1 x-ray (12.97 keV). The system includes two detectors – one for each collection channel – allowing separate and simultaneous measurements of uranium and thorium L-alpha-1 x-ray signal intensities. In this paper, the measurement uncertainty of uranium/thorium ratios using dual-channel MWDXRF is examined in detail. Relative contributions of measurement configuration, specimen homogeneity, uniformity of droplet deposition, size of dried deposit, and self-attenuation are considered. Curves of predicted measurement precision versus concentration (for various uranium/thorium ratios) are discussed. The anticipated performance of the Dual-Channel MWDXRF actinide ratio instrument is contrasted with x-ray analytical techniques currently in use by nuclear safeguards agencies.