A new thorium-229 reference material.

Area of Science:

• Nuclear Chemistry
• Analytical Chemistry
• Radiochemistry

Background:

• Accurate quantification of thorium isotopes is essential for nuclear forensics.
• Reference materials are critical for validating analytical methods and ensuring data reliability.
• Thorium-229 (²²⁹Th) is a key isotope used as a spike in isotope dilution mass spectrometry (IDMS).

Purpose of the Study:

• To characterize a new reference material for ²²⁹Th molality.
• To determine ²²⁹Th, ²³⁰Th, and ²³²Th isotope amount ratios in the reference material.
• To provide a reliable standard for nuclear forensic analyses using IDMS.

Main Methods:

• Characterization of ²²⁹Th molality using precise solution preparation.
• Determination of thorium isotope amount ratios (n(²³⁰Th)/n(²²⁹Th) and n(²³²Th)/n(²²⁹Th)) using mass spectrometry.
• Uncertainty evaluation following established metrological guidelines (k=2).

Main Results:

• The ²²⁹Th molality was determined to be (1.1498 ± 0.0016) × 10⁻¹⁰ mol g⁻¹.
• The n(²³⁰Th)/n(²²⁹Th) isotope ratio was measured as (5.18 ± 0.26) × 10⁻⁵.
• The n(²³²Th)/n(²²⁹Th) isotope ratio was found to be (3.815 ± 0.092) × 10⁻⁴.

Conclusions:

• A new reference material with certified ²²⁹Th molality and thorium isotope ratios has been established.
• This material serves as a reliable ²²⁹Th spike for isotope dilution mass spectrometry in nuclear forensics.
• The characterized values and uncertainties support accurate and traceable measurements in forensic applications.