Sample preparation for actinide isotopic analysis using FIB-SEM

Area of Science:

• Nuclear Chemistry
• Materials Science
• Analytical Chemistry

Background:

• Accurate isotopic analysis of uranium dioxide (UO2) is crucial for nuclear fuel cycle applications.
• Existing techniques often require larger sample sizes, limiting spatial resolution.
• The need for sensitive methods to analyze nanogram-scale samples of radioactive materials persists.

Purpose of the Study:

• To establish capabilities for extracting and analyzing nanogram-scale UO2 samples for spatial isotopic analysis.
• To adapt existing techniques for handling alpha-emitting radioactive materials.
• To assess the precision and accuracy of isotopic measurements on micro-samples.

Main Methods:

• Utilized a Helios 5CX Focused Ion Beam Scanning Electron Microscope (FIB-SEM) adapted for radioactive materials to extract 2-80 ng UO2 samples from a depleted pellet.
• Employed Thermal Ionization Mass Spectrometry (TIMS) for isotopic composition analysis.
• Applied Triple Quadrupole Inductively Coupled Mass Spectrometry (ICP-QQQ-MS) for isotopic ratio measurements.

Main Results:

• TIMS successfully measured weight percentages of 234U, 235U, 236U, and 238U with relative standard uncertainties (RSU) ranging from 0.26% to 11%.
• ICP-QQQ-MS determined the 235U/238U ratio with an RSU of 37.4%.
• Demonstrated feasibility of isotopic analysis on sub-microgram UO2 samples.

Conclusions:

• Developed and validated a methodology for spatial isotopic analysis of nanogram-scale UO2 samples.
• The established techniques provide valuable data for understanding material composition at a micro-scale.
• This work advances the field of nuclear material characterization and safeguards.