Highly-sensitive uranium isotopic analysis for nuclear safeguards

Significance of the Topic

Highly precise uranium isotope measurements underpin nuclear material accountancy and safeguards to detect undeclared activities and ensure compliance with nonproliferation treaties. Achieving reliable isotopic ratios from minute uranium quantities enhances the ability of analytical laboratories to monitor and verify nuclear materials.

Objectives and Overview of the Study

This study assessed the analytical performance of a high-sensitivity multicollector inductively coupled plasma mass spectrometer for uranium isotope analysis. The main goal was to demonstrate accurate and precise measurement of U234 U235 and U236 abundances relative to U238 in sample solutions containing only two nanograms of uranium.

Methodology

A standard bracketing approach was used with the NBS U030 reference material and a CRM U010 sample at 2.3 nanograms per gram in three percent nitric acid. Faraday cups collected signals for U238 and U235 while secondary electron multipliers measured U234 and U236 with low abundance sensitivity achieved through ion energy filtering. A certified one microgram per liter uranium solution provided calibration for signal intensity and sample utilization efficiency was estimated.

Instrumentation

• Multicollector ICP-MS equipped with a Jet Interface featuring high performance interface pump and sample skimmer cones
• Self-aspirating microflow nebulizer and desolvating nebulizer system for solution introduction
• Automated sample handling with an autosampler
• A detector array combining compact discrete dynode ion counters and full-sized secondary electron multipliers with dual ion energy filters

Main Results and Discussion

Ten replicate analyses of the NBS U010 sample yielded mean atomic ratios of U234/U238 at 5.43E-05 with 0.08 percent relative standard deviation U235/U238 at 0.01014 with 0.012 percent RSD and U236/U238 at 6.91E-05 with 0.08 percent RSD. The scatter of measured values remained within the certified uncertainties of reference materials and recent literature values. High sensitivity from the Jet Interface did not compromise accuracy and met International Atomic Energy Agency target values for measurement uncertainties in safeguards.

Benefits and Practical Applications

Performing precise isotope ratio analysis on subnanogram uranium samples enables laboratories to reduce sample consumption and accelerate throughput. The demonstrated stability and sensitivity support nuclear forensics environmental monitoring and safeguards laboratories in verifying material provenance and tracking small sample inventories.

Future Trends and Applications

Advancements in detector technology and interface design may lower detection limits further and improve abundance sensitivity. Integration with automated sample preparation systems and data processing workflows will enhance throughput and consistency. Expanded coupling with separation techniques could broaden applications to complex matrices and environmental samples.

Conclusion

The high-sensitivity multicollector ICP-MS with Jet Interface delivers robust uranium isotope precision and accuracy from minimal sample amounts. Its performance meets stringent safeguards requirements and offers a powerful tool for nuclear analytical laboratories.

References

1. International Atomic Energy Agency 2010 International Target Values for Measurement Uncertainties in Safeguarding Nuclear Materials STR-368
2. Richter S Goldberg SA 2003 International Journal of Mass Spectrometry 229 181–197