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Ultrahigh-Energy X-ray Fluorescence


Figure 1 : End-on view of the UHEXRF experimental setup at APS 6-ID-D beam line, which shows the sample mounted on multiple translation stages for positioning of the sample, a camera to observe sample location, detector, and in the upper-left background the entrance of the synchrotron beam.


dwell time. T e programmable slits allow selectable spot sizes down to 25 µm.


Spectrum acquisition and analysis . A high-purity germanium detector (Canberra model GL0110S) with a resolution of around 1 keV, equipped with digital signal processor and acquisition interface module electronics, was used to collect the emitted X-ray fl uorescence. In-house APS (EPICS) soſt ware was used to control the data acquisition. T e data was processed with user-developed Matlab scripts to calibrate each spectrum, fi t the peaks, remove background, and generate net intensities used for creating elemental maps. Of particular concern was the overlap from the Compton scatter peak, which was centered ~87 keV. T e wings of the Compton peak extended for 1–2 keV on either side of the centroid and thus must be removed before each spectrum is processed. Figure 2 shows the measured spectrum and the background. T is full spectrum illustrates the separation of the typical low-energy spectra normally used to characterize U L-series at 13.6 keV compared with the UHEXRF U Kα 1 line at ~98 keV used in this work. T e Compton scatter peak along with the tails is visible at ~87 keV.


Results


Uranium detection . Figure 3 shows an overlay of a bare uranium spectrum (solid line) with a spectrum acquired with 1.3 mm of Zircaloy shielding (dashed line) in front of the sample. T e Zircaloy shielding decreases the uranium signal by almost 80%, and there is a signifi cant increase in Compton scatter. However, the uranium peaks are still clearly visible, even with twice the nominal thickness of conventional nuclear fuel rod cladding. T us the detection of uranium in typical nuclear fuel rods is quite feasible. Calibration measurements . An example of one of the uranium maps of the dried residue deposits is shown in Figure 4 . T e total uranium mass in the deposit is around 99 ng. T e elemental map indicates the residue is not uniform with several hot spots. However by summing the region of interest for the uranium peak over all the pixels in the elemental map, a


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summed intensity count rate was obtained for each calibration sample. Even though a relatively small volume deposit was used, only 1 μ L, the deposit covers a rather large area of almost 3 mm in diameter. T e results of the calibration measurements on both the aqueous and SSF spiked dried residues are shown in Figure 5 . T is fi gure is a plot of the intensity (counts/sec) for each known mass of uranium in the deposit. Although the aqueous and SSF matrices are quite diff erent, the correlation coeffi cient for the log-log plot is ~0.972. T is demonstrates the quantitative analysis capability of UHEXRF within the context of the matrix eff ects.


X-ray maps of the mock fuel rod . T ese results have demonstrated the qualitative and quantitative capabilities of UHEXRF. However, the ability to actually characterize a


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Figure 2 : Full UHEXRF spectrum of an aqueous uranium dried spot residue showing both low- and high-energy U lines, which have been labeled. The red line designates the UHEXRF cutoff energy of 80 keV.


Figure 3 : UHEXRF spectrum overlay of uranium for a bare sample (solid line) and a 1.3 mm thick Zircaloy shielded sample (dashed line). This thickness is twice the normal thickness of nuclear fuel rod cladding. The U signal decreases by almost 80% with the Zircaloy shielding, however the U signal is still detected.


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