Analytical considerations in the determination of uranium isotope ratios in solid uranium materials using laser ablation multi-collector ICP-MS

Abstract

Validated analytical measurement protocols for the fast and accurate determination of the uranium (U) isotopic composition ( 234 U, 235 U, 236 U, 238 U) of solid nuclear materials were developed employing ns-laser ablation (LA) coupled to multi-collector ICP-MS. The accuracy of the analytical procedure was assured by frequent ( n = 65) analysis of a pressed pellet of certified isotopic reference material CRM U-030 (∼3 wt% 235 U). The expanded uncertainty ( k = 2) for the n ( 235 U)/ n ( 238 U) ratio was as low as 0.05%, rising to 0.62% and 1.09% for n ( 234 U)/ n ( 238 U) and n ( 236 U)/ n ( 238 U) ratios, respectively. LA-MC-ICP-MS measurements of a pressed pellet of certified isotopic reference material CRM U-020 (∼2 wt% 235 U) before analysis of each sample allowed calculation of the ion counter gains and mass bias correction. Both individual spot analysis and line scan analysis were used to measure n ( 234 U)/ n ( 238 U), n ( 235 U)/ n ( 238 U), and n ( 236 U)/ n ( 238 U) ratios in two low-enriched UO 2 pellets from the fourth Collaborative Materials Exercise (CMX-4), four seized low-enriched UO 2 pellets intercepted from illicit trafficking and one metal sample consisting of depleted U. LA-MC-ICP-MS results of all investigated samples matched well with U isotope ratios obtained by thermal ionisation mass spectrometry (TIMS). This independent confirmation of the LA-MC-ICP-MS results by TIMS underpinned the high quality of generated analytical data. Acquisition of several thousand data points within a couple of minutes during line scan analysis yielded detailed information on the spatial distribution of the U isotopic composition of selected UO 2 pellets, revealing straightforwardly their (in˗)homogeneity on the μm-scale. Calculating skewness and half width of the frequency distributions of the n ( 235 U)/ n ( 238 U) amount ratio allowed the quantitative assessment of the (in-)homogeneity of the investigated samples. This information allows drawing conclusions on the starting materials used for the production of the pellets. From a nuclear forensics perspective, LA-MC-ICP-MS provides quick, accurate results on the spatial di...

Single shot laser ablation MC-ICP-MS for depth profile analysis of U isotopes in UO2 single crystals

“…At such low uences, uctuations may be expected that are liable to have an essential impact on the laser ablation rate. 8 Compared to our previous work, [10][11][12] the carrier gas of the LA unit was changed from Ar to He in this study. The use of He instead of Ar is known to change the aerosol expansion and to improve the transport efficiency.…”

“…Further experimental details were reported earlier. [10][11][12] The Faraday detectors of a double-focusing multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS, Nu Plasma™, NU Instruments, Wrexham, Wales, U.K.) measured the abundance of 235 U and 238 U in the ablated particle cloud. Before switching to LA, the MC-ICP-MS was tuned for sensitivity and stability of U signals in solution mode employing an aqueous 30 ng L À1 U calibration solution having natural U isotopic composition.…”

“…Additional information can be found elsewhere. [10][11][12] A minimum of ve sets of LA-MC-ICP-MS experiments were conducted for each parameter reported in this study. The signal intensities of 235 U and 238 U were recorded with the time-resolved-analysis option of MC-ICP-MS soware.…”

“…1 Nowadays, the accurate and precise determination of the elemental and/or isotopic composition of advanced crystalline materials is of utmost importance to guarantee their properties and to identify potential contaminants. [2][3][4][5][6][7][8][9][10][11][12] Classical analytical approaches employing dissolution of a fragment of such materials followed by subsequent chemical analysis are not effective because their features are captured either in thin (nm to mm thick) layers or within local hot spots. Therefore, solid sampling techniques such as Electro-Thermal Vaporisation (ETV) or Laser Ablation (LA) are employed frequently for this purpose.…”

“…7 The lateral resolution of a few mm enables identifying potential inhomogeneity within a sample, with extended line scan analysis providing results reecting bulk analysis. 11,12 In addition, depth proling capabilities of LA provide sub-mm depth resolution. 4,[6][7][8] Despite all of its advantages, LA-ICP-MS suffers from some important limitations such as non-uniform ablation processes and matrix-dependent melting events.…”