Uranium particle age dating, aggregation, and model age best estimators

Area of Science:

• Geochemistry
• Nuclear Science
• Analytical Chemistry

Background:

• Uranium particle age dating is vital for International Nuclear Safeguards.
• Large-Geometry Secondary Ion Mass Spectrometry (LG-SIMS) is a key technique.
• Existing methods face challenges with small, young, or low-enriched particles.

Purpose of the Study:

• To identify factors causing bias and uncertainty in LG-SIMS uranium particle age dating.
• To introduce and validate a new model age estimator, 'mid68'.
• To enhance the reliability of chronometric data for nuclear applications.

Main Methods:

• Analysis of simulated and actual uranium particle samples.
• Investigation of surface chemistry evolution effects on Th/U measurements.
• Evaluation of detector background and particle aggregation methods.
• Development and application of the 'mid68' age estimator using Feldman and Cousins or Bayesian methods.

Main Results:

• Evolving surface chemistry, detector background, and aggregation impact age estimates.
• The 'mid68' estimator provides a robust 'best estimate' and symmetric uncertainty.
• Mid68 is particularly valuable for particles with low 230Th counts and asymmetric age distributions.

Conclusions:

• The 'mid68' estimator offers improved accuracy and uncertainty quantification for uranium particle dating.
• This work addresses critical metrology aspects for nuclear safeguards applications.
• The findings support the establishment of robust particle chronometry capabilities in analytical laboratories.