Rapid Analysis of Actinide Isotopes in Post-Detonation Debris Samples by RIMS

A team of researchers led by Michael R. Savina from the Lawrence Livermore National Laboratory has developed a method to rapidly analyze the isotopic compositions of uranium (U), plutonium (Pu), and americium (Am) in post-detonation debris samples. Their findings have been published in the Journal of Analytical Atomic Spectrometry (1).

The researchers demonstrated their technique on solid basalt matrices spiked with trace amounts of uranium, plutonium, and americium to mimic post-detonation debris. They were able to accurately analyze materials containing parts-per-million (ppm) to parts-per-billion (ppb) levels of actinides without separating them from the host matrix, using less than 100 nanograms of sample material. The measured isotopic compositions of U, Pu, and Am were accurate to within 10%, except for the ²³⁸Pu isotope, which was compromised by low concentration and excesses of ²³⁸U up to 34,000:1.

To accurately measure the ²³⁸Pu/²³⁹Pu ratio in the sample, the team developed a new method called “blinking” that takes advantage of the unique ability of resonance ionization mass spectrometry (RIMS) to rapidly and accurately quantify the backgrounds from all sources. The method was successfully used to measure the ²³⁸Pu/²³⁹Pu ratio on a sample containing 1.4 × 10⁶ atoms of ²³⁸Pu at a concentration of 0.1 ppb in the host material.

RIMS is a highly sensitive analytical technique used for the detection and quantification of trace elements and isotopes. It uses laser light to ionize atoms or molecules of interest, leading to their separation and detection based on their mass-to-charge (m/z) ratio. RIMS can detect extremely low concentrations of isotopes, making it useful for applications in environmental monitoring, nuclear forensics, and isotopic analysis in geology and cosmology. RIMS can also be coupled with other mass spectrometry techniques, such as time-of-flight and quadrupole mass spectrometry, to enhance its sensitivity and selectivity.

Although traditional mass spectrometry is currently the most accurate and precise method for determining actinide isotopic compositions, it typically requires time-consuming dissolution and chemical purification prior to analysis. However, RIMS has been used to measure isotope ratios in mixed actinide samples without chemical purification. It has also demonstrated the ability to measure ²⁴¹Pu and ²³⁸Pu in both pure standard materials and spent nuclear fuel, including spent fuel particles from the Chernobyl Exclusion Zone that have significant environmental exposure.

This work represents an important step forward in the rapid analysis of post-detonation debris samples, where the actinides are present as trace elements in an environmental matrix and the ²³⁸U/²³⁸Pu is significantly higher than 4000. The team's RIMS method offers a promising alternative to the traditional methods of isotope analysis, which are time-consuming and require significant amounts of sample preparation.

Reference

(1) Savina, M. R.; Shulaker, D. Z.; Isselhardt, B. H.; Brennecka, G. A. Rapid isotopic analysis of uranium, plutonium, and americium in post-detonation debris simulants by RIMS. J. Anal. At. Spectrom. 2023, ASAP. DOI:10.1039/D3JA00096F