²³⁷Np analytical method using ²³⁹Np tracers and application to a contaminated nuclear disposal facility

Area of Science:

• Environmental analytical chemistry
• Radiochemistry
• Nuclear science

Background:

• Environmental analysis of Neptunium-237 (237Np) is difficult due to low concentrations.
• A reliable chemical yield tracer is needed for accurate 237Np measurements.

Purpose of the Study:

• To develop a rapid, inexpensive analytical method for environmental 237Np.
• To employ Neptunium-239 (239Np) as a chemical yield tracer.

Main Methods:

• Utilized short-lived 239Np (t1/2 = 2.3 days) as a tracer, separated from Americium-243 (243Am) and standardized via gamma spectrometry.
• Employed microwave digestion (900 W) for rapid sample preparation (99.8% yield).
• Used chromatographic separations for high Np/U separation factors (>10^6) and quantified 237Np via inductively coupled plasma-mass spectrometry (ICP-MS).

Main Results:

• Achieved high digestion yields (99.8% ± 0.1%) and total Np yields (95% ± 4%).
• Detected low-level 237Np contamination in soil samples near the Subsurface Disposal Area at Idaho National Laboratory.
• Observed maximum 237Np concentrations significantly exceeding fallout levels (up to 10^3 times higher).

Conclusions:

• The developed method provides a rapid, cost-effective approach for environmental 237Np analysis.
• The study confirms 237Np contamination in soils surrounding a radioactive waste disposal site.
• This technique is valuable for environmental monitoring and risk assessment of radioactive contamination.