Ultra-low level plutonium isotopes in the NIST SRM 4355A (Peruvian Soil-1)

Area of Science:

• Environmental Science
• Analytical Chemistry
• Nuclear Metrology

Background:

• NIST Standard Reference Material (SRM) 4355 Peruvian Soil has been essential for radionuclide monitoring for over 20 years.
• Its low fallout contamination makes it an ideal soil blank for terrestrial pathway studies.
• SRM 4355 is currently out of stock, necessitating the development of a successor.

Purpose of the Study:

• To develop and characterize a new batch of Peruvian Soil as NIST SRM 4355A.
• To provide environmental radioanalytical laboratories with a reliable blank material for contamination and detection limit assessments.
• To supply the mass spectrometry community with a crucial material for ultra-low plutonium quantification, method development, and quality control.

Main Methods:

• Quantification of ultra-low plutonium content in SRM 4355A presented significant challenges.
• Methods involved meticulous blank control and correction.
• Addressing isobaric interferences, ensuring instrument stability, and performing rigorous peak and detection assessments were critical.

Main Results:

• A systematic statistical evaluation of measurement results was conducted.
• Extensive discussions with mass spectrometry metrologists were held to derive certified values.
• The one-sided upper limit of the 95% tolerance with 95% confidence for the massic 239Pu content in SRM 4355A was estimated at 54,000 atoms/g.

Conclusions:

• SRM 4355A Peruvian Soil is vital for both environmental radioanalytical and mass spectrometry applications.
• The development ensures continued availability of a critical reference material for sensitive radionuclide measurements.
• Accurate quantification of trace plutonium levels is achievable with advanced metrological techniques.