Evaluation of the Homogeneity of the Uranium Isotope Composition of NIST SRM 610/611 by MC-ICP-MS, MC-TIMS, and SIMS

Abstract

Abstract:As analytical and microanalytical applications employing uranium isotope ratios increase, so does the need for reliable reference materials, particularly in the fields of geochemistry, geochronology, and nuclear forensics. We present working values for uranium isotopic data of NIST 610/611 glass, collected by multicollector inductively-coupled plasma mass spectrometry (MC-ICP-MS), multicollector thermal ionization mass spectrometry (MC-TIMS), and secondary ion mass spectrometry (SIMS). The presence of depleted U, and, in this case, measureable 236 U, makes NIST 610/611 an ideal candidate for a uranium isotopic reference material for nuclear materials. We analyzed multiple chips of three different NIST 611 wafers and found no heterogeneity in U within or between the wafers, within analytical uncertainty. We determined working values and uncertainties (using a coverage factor of two) using data from this study and the literature for the following U isotope ratios:

A NanoSIMS 50 L Investigation into Improving the Precision and Accuracy of the 235U/238U Ratio Determination by Using the Molecular 235U16O and 238U16O Secondary Ions

“…For the NIST-610 glass, which was only analyzed using the 200 pA beam current, the average 235 U/ 238 U and 235 U 16 O/ 238 U 16 O ratios and associated 1σ uncertainties were 0.00283 ± 0.00028 and 0.00340 ± 0.00020. Considering uranium occurs at the parts per million level in the NIST-610 glass and that only a 200 pA primary beam current was used, both values compare well with the published 235 U/ 238 U ratio of 0.00239 [21] (note the uncertainty of the published ratio is in the seventh decimal place). For the NIST-610 glass, the average 1σ uncertainty of the individual 235 U/ 238 U ratios is slightly higher at 0.00084 compared to the 235 U 16 O/ 238 U 16 O ratios at 0.00067.…”

“…While solution data was not obtained for the NIST-610 glass and Plesovice zircon reference materials analyzed in this study, there is an LG-SIMS 235 U/ 238 U ratio available for the NIST-610 glass published in [21], whereas the Plesovice zircon (described in [22]) can be assumed to have a natural 235 U/ 238 U ratio. For the NIST-610 glass, which was only analyzed using the 200 pA beam current, the average 235 U/ 238 U and 235 U 16 O/ 238 U 16 O ratios and associated 1σ uncertainties were 0.00283 ± 0.00028 and 0.00340 ± 0.00020.…”

“…In Figures 7 and 8, each analysis of 235 U/ 238 U and 235 U 16 O/ 238 U 16 O and its associated 1σ uncertainty for the UF4 (Figure 7a,b) and UO2(NO3)2•6(H2O)3 (Figure 8a,b) is shown. In Figure 9, each analysis of 235 U/ 238 U and 235 U 16 O/ 238 U 16 O and its associated 1σ uncertainty for the NIST-610 glass (Figure 9a,b) is shown relative to the reference 235 U/ 238 U of 0.00239, which is the average LG-SIMS value reported in [21]. In Figure 10, each analysis's 235 U/ 238 U and 235 U 16 O/ 238 U 16 O and its associated 1σ Figure 9, each analysis of 235 U/ 238 U and 235 U 16 O/ 238 U 16 O and its associated 1σ uncertainty for the NIST-610 glass (Figure 9a,b) is shown relative to the reference 235 U/ 238 U of 0.00239, which is the average LG-SIMS value reported in [21].…”

“…In Figure 9, each analysis of 235 U/ 238 U and 235 U 16 O/ 238 U 16 O and its associated 1σ uncertainty for the NIST-610 glass (Figure 9a,b) is shown relative to the reference 235 U/ 238 U of 0.00239, which is the average LG-SIMS value reported in [21]. In Figure 10, each analysis's 235 U/ 238 U and 235 U 16 O/ 238 U 16 O and its associated 1σ Figure 9, each analysis of 235 U/ 238 U and 235 U 16 O/ 238 U 16 O and its associated 1σ uncertainty for the NIST-610 glass (Figure 9a,b) is shown relative to the reference 235 U/ 238 U of 0.00239, which is the average LG-SIMS value reported in [21]. In Figure 10, each analysis's 235 U/ 238 U and 235 U 16 O/ 238 U 16 O and its associated 1σ uncertainty for Plesovice zircon reference material (Figure 10a,b) is analyzed using the 200 pA primary beam current is shown relative to the natural 235 U/ 238 U of 0.00726, which is the consensus value reported in [23].…”

“…The NIST-610 glass and Plesovice zircons are widely used reference materials in the geosciences. Specific to this study, the uranium isotopic composition of the NIST-610 glass is 235 U/ 238 U = 0.0023956 ± 0.0000005, determined by [21]. The uranium concentration of the Plesovice zircon is described in [22], and the zircon is assumed to a have a natural 235 U/ 238 U ratio of 0.0072549 ± 0.0000008, which is the consensus value reported in [23].…”