水、溶液、待测液中U 同位素检测方案(等离子体质谱)

Authors： M. Paul Field (field@icpms.com)1， Nicholas S. Lloyd (nicholas.lloyd@thermofisher.com)， and Paul Watson1 Recent Developments in MC-ICP-MS for Uranium Isotopic Determination from Small Samples Poster Presented at American Geophysical Union San Francisco 2016 Uranium isotope ratio determination for nuclear forensics，nuclear safeguards and for environmental applications canbe challenging due to the large isotopic differences betweensamples and because of the low abundance of 234U and236U. For some applications the total uranium quantities canbe limited， or it is desirable to run at lower concentrationsfor radiological protection. Recent developments in inletsystems and detector technologies allow small samples tobe analyzed at higher precisions using MC-ICP-MS. Here we evaluate the combination of Elemental Scientificapex Q desolvation system and microFAST MC dual loop-loading flow-injection system with the Thermo ScientificNEPTUNE Plus MC-ICP-MS. The inlet systems allow forthe efficient handling of small sample volumes with efficientdesolvation to minimize the hydride interference on 236U. Thehighest ICP sampling efficiency is realized using the ThermoScientific Jet Interface. Thermo Scientific 1013 ohm amplifier technology allows smallion beams to be measured at higher precision， offering thehighest signal/noise ratio with a linear and stable responsethat covers a wide dynamic range (ca. 1 kcps -30 Mcps). For nanogram quantities of low enriched and depleteduranium standards the 235U was measured with 1013 ohmamplifier technology. The minor isotopes (234U and 236U) weremeasured by SEM ion counters with RPQ lens filters， whichoffer the lowest detection limits. For sample amounts ca. 20ng the minor isotopes can be moved onto 1013 ohm amplifiersand the 235U onto standard 101 ohm amplifier. To illustrate theapplication a set of solutions from environmental particles [1]were analyzed， the use of precise three isotope ratio plotsallows for source attribution with increased confidence. lsotope ratio determination made using a Thermo ScientificNEPTUNE Plus MC-ICP-MS， with Jet Interface and ElementalScientific apex Q high-efficiency desolvating nebulizer system.Samples and standards were diluted in 3 wt.% HNO， to ca. 25ng/g uranium concentration. Four 'sample' measurements werebracketed by measurement of the NBS U-010 standard and ablank.Each measurement consisted of two 30-second half-mass off-peak baselines and 7-minutes on-peak acquisition.1013 ohm amplifier technology was used for the quantificationof 234U and 236U. Sample measurements were corrected， ratioagainst ratio， using the NBS U-010 values determined byRichter and Goldberg (2003). Uncertainty was propagated fromthe isotope ratio measurements and the standard referencevalues. Sensitivity was ca. 1600 V/ppm at 119 pl/min nebulizeruptake rate， with a UO/U ratio of ca. 1% and negligible hydride.The 3.5 E-07 LoQ for 236U/238U was determined from repeatmeasurement of NBS U-0002. The drift of 235U/238U over thestandard measurement sequence was ca. 22 ppm/hour (2RSD). Figure 1. Thermo Scientific NEPTUNE Plus MC-ICP-MS withElemental Scientific microFAST MC and apex Q. The nebulized solution was introduced to the NEPTUNE Plus viaan apex Q desolvating system. The apex Q integrates heating，condensing， and membrane desolvation with complete softwarecontrol for high precision remote tuning. Mass Spectrometry A Thermo Scientific NEPTUNE Plus MC-ICP-MS with JetInterface Option was used. The high-sensitivity Jet sample andX-type skimmer cones in combination with the apex providethe highest sensitivity. This combination is recommended for Uisotope precision. Figure 2. Nd sensitivity and oxides using Thermo Scientific JetInterface with ESl apex Q. Figure 3. apex Q screenshot showing software control for precise gas tuning. Stability Figure 4. 234U/238U measured with 131 kcps (2mV) 234U on 1013 amplifier from 25 ng/g NBS U-01092x 10-minute runs spanning 15.5 hoursRaw Ratio RSD： 0.04% (external)， 2SE error bars (internal) Figure 5. Greater than 5 orders of magnitude wash outobtained within 1 minute of running a 1 ppm uranium samplefor 4 minutes. Table 1. Note that the certified reference values for NBS U-010 would change the mean values and expand the uncertainty significantlyfor 234U/238U and 236U/238U. CRM Accuracy and Precision 243U/238U 235U/238U 236U/238U NBS U-005 Mean 0.000021889 0.00491913 0.000047459 SD 0.000000032 0.00000024 0.000000038 RSD 0.15% 0.005% 0.08% NBS U-0002 Mean 0.000001653 0.00017724 SD 0.000000042 0.00000016 RSD 2.5% 0.09% IRMM-184 Mean 0.000053230 0.00726026 <3.5E-7 SD 0.000000049 0.00000016 RSD 0.09% 0.002% IRMM-183 Mean 0.000019824 0.00321731 0.000148529 SD 0.000000050 0.00000019 0.000000037 RSD 0.25% 0.006% 0.02% Solution samples were obtained from the dissolution ofuranium oxide grains isolated from soil and dust samplecollected in the vicinity of Colonie， NY， USA. The soil anddust samples were contaminated by the combustion of scrapuranium metal at a former National Lead Industries (NLI)plant that operated from 1958-1984. The environmentalcase study is described in detail by Lloyd et al. (2009a). Theprocedures for the isolation of the 20-65 um diameter grainsand the chemical separation of uranium is described in Lloyd et al. (2009b). The isotopic compositions of the individualuranium oxide grains are all from depleted uranium with236U incorporated from reprocessed uranium. The isotopiccomposition are compatible with the tails assays from thePaducah Gaseous Diffusion Plant (PGDP) and the mixing ofthese materials at the former NLI plant at Colonie. Preciseminor isotope data and the plots of three isotope ratiosincreases confidence in source apportionment. Isotopic Compositions Figure 6. Isotopic Compositions of Colonie UOx Grains(blue) and PGDP tails assays (red). Figure 7. Isotopic Compositions of IndividualUraniumOxide Grains. Conclusions · An experimental setup was optimized for precise andaccurate determination of uranium isotope ratios fromsingle uranium oxide grains. · The ESl apex Q is a new high-efficiency desolvatingnebulizer system， offering low-oxides， low hydrides， andhighest sensitivity up to 250 pl/min introduction rate. ·The sensitivity and stability of the inlet system and ICPinterface is utilized by ion detection on detectors thathave complimentary performance characteristics. Thecombination with Thermo Scientific 1013 ohm amplifiertechnology allows minor isotopes to be measured moreprecisely from limited samples. · The ESl apex Q is tuned via software for preciseoptimization. The stability of gas flow regulation isproven by 235U/238U mass bias stabilities that aretypically better than 60 ppm (1RSD) over analyticalsessions of 15+ hours. References Richter & Goldberg 2003， Int.J. Mass Spectrom.，229， 181-197. Lloyd et al.， 2009a， Sci. Total Environ.， 408(2)， 397-407. Lloyd et al.， 2009b， J. Anal. At. Spectrom.， 24(6)， 752-758. ( C Elemental Scientific 7277 World Communications Drive Omaha， NE 68122 Tel：1-402-991-7800 sales@icpms.com www.icpms.com ) lemental Scientific， World Communications Drive， Omaha， Nebraska USA. Thermo Fisher Scientific， Hanna-Kunath-Str. Bremen， Germany. 在核鉴定，核安全和环境应用方面，对铀同位素比值测定因样品之间的同位素差异大，234U和236U的丰度低而具有极大挑战性。在某些应用领域，U含量较少，可以在较低 U 含量下进行工作，并且可以防护。样品引入系统与检测系统的发展使得 MC-ICP-MS 以更高精度分析微量样品成为可能。在此，我们对Elemental Scientifc apex Ω 去溶系统、microFAST MC 双环进样流动注射系统以及 Thermo Scientifc NEPTUNE Plus MC-ICP-MS 系统的组合进行评价。该进样系统可以高效处理微量的样品，高效溶剂去除可以极大限度地减少氢化物对236U的干扰。ICP 高效的采样效率通过使用热电公司采样锥实现。热电公司 1013Ω 放大器技术可以实现小离子束更高精度的测量并提供高信噪比和在很宽的线性范围（1 Kcps-30Mcps）内稳定的信号输出。对于纳克量级的低浓缩铀和贫化铀标准，235U 通过 1013Ω 方法技术检测。微量同位素 （234U、236U） 通过具有 RPQ 滤质透镜的 SEM 离子计数器进行检测。对于大约 20 ng 的样品量的样品，微量同位素利用 1013Ω 放大器检测，235U 利用标准的 1011Ω 的放大器检测。为了说明该装置的应用，我们分析了一组环境粒子，使用三个同位素比值作图进行溯源，结果更为可靠。