Measurement of the isotopic composition of uranium micrometer-size particles by femtosecond laser ablation-inductively coupled plasma mass spectrometry

In this paper, we will describe and indicate the performance of a new method based on the use of femtosecond laser ablation (fs-LA) coupled to a quadrupole-based inductively coupled plasma mass spectrometer (ICP-QMS) for analyzing the isotopic composition of micrometer-size uranium particles. The fs-LA device was equipped with a high frequency source (till 10 kHz). We applied this method to 1–2 μm diameter-uranium particles of known isotopic composition and we compared this technique with the two techniques currently used for uranium particle analysis: Secondary Ionization Mass Spectrometry (SIMS) and Fission Track Thermal Ionization Mass Spectrometry (FT-TIMS). By optimizing the experimental conditions, we achieved typical accuracy and reproducibility below 4% on 235U/238U for short transient signals of only 15 s related to 10 to 200 pg of uranium. The detection limit (at the 3 sigma level) was ~ 350 ag for the 235U isotope, meaning that 235U/238U isotope ratios in natural uranium particles of ~ 220 nm diameter can be measured. We also showed that the local contamination resulting from the side deposition of ablation debris at ~ 100 μm from the ablation crater represented only a small percentage of the initial uranium signal of the ablated particle. Despite the use of single collector ICP-MS, we were able to demonstrate that fs-LA-ICP-MS is a promising alternative technique for determining uranium isotopic composition in particle analysis.