Characterization and Optimization of a Spectral Window for Direct Gaseous Uranium Hexafluoride Enrichment Assay Using Laser-Induced Breakdown Spectroscopy

Abstract

Through a systematic scanning of 235U and 238U emission lines between 280 nm and 745 nm, the optimal emission line for direct gaseous uranium hexafluoride (UF6) enrichment assay using laser-induced breakdown spectroscopy (LIBS) was found. Screening for spectral features that are potentially useful for U isotopic analysis was gauged from the magnitude of the 235U–238U isotopic shift and the signal-to-background ratio of the emission line through a parameter termed ΔSBR 235U–238U. The ΔSBR spectrum shows peaks at wavelength positions where there are strong lines with significant 235U–238U shifts. The screening identified 13 spectral-window candidates, which were down selected based on their overall accuracy in predicting the 235U enrichment of three UF6 samples of natural (0.720 atom% 235U) and low-enriched (4.675 atom% and 9.157 atom% 235U) grades. The U(I) 646.498 nm emission line, with a determined 235U–238U isotopic shift of −17.7 pm, was found to be the optimal spectral window for direct UF6 enrichment assay. The root mean square error for enrichment assays on the three natural and low-enriched UF6 samples, with each sample measured in six replicates, was 0.31% in absolute 235U content. Each measurement comprised LIBS signals accumulated from 3000 laser shots. The analytical bias and precision were better than 0.5% and 0.3%, respectively, in absolute [235U/(235U + 238U)] ratios. Specific for the two low-enriched UF6 samples, the relative standard deviations from six replicated measurements were around 2%.

Laser Ablation Plasmas and Spectroscopy for Nuclear Applications

“…Chan et al recently made a significant stride, reaching measurement accuracies within 0.5% of the known 235U/( 235U+ 238U) ratios using ns-LIBS. 265–269 Jordan et al report an analogous study using fs-LIBS in an attempt to achieve greater stability with the gaseous measurements over a larger pressure range. 270 Both groups used multivariate nonlinear spectral fittings to derive enrichment directly from the spectra without calibration samples.…”

Atomic spectrometry update: review of advances in the analysis of metals, chemicals and materials

“…Accurate and precise isotopic ratio measurements remains a valuable area for determining the source of nuclear contamination. Mass spectrometric techniques were dominant, but other techniques including LIBS 185,186 and X-ray based techniques were also successfully applied. 187 The measurement of U and transuranic isotopic ratios was the subject of a number of studies.…”

Novel Calibration Approach for Monitoring Aerosol Hydrogen Isotopes Using Laser-Induced Breakdown Spectroscopy for Molten Salt Reactor Off-Gas Streams

“…Although LIBS is used primarily as an elemental technique, for specific elemental and molecular emissions, a wavelength shift can be measured and modeled to evaluate isotope contributions. In the last decade, a significant effort in the LIBS community has revolved around isotopic measurements via LIBS and its extension, laser ablation molecular isotopic spectroscopy (LAMIS) [ 9 , 10 , 11 , 12 , 13 , 14 , 15 ]. LIBS isotope measurements are performed using shifts in the emission peaks; LAMIS uses peak shifts of molecular emissions, which occur later in the plasma lifetime but present larger shifts [ 10 ].…”