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D6239-09 – Standard Test Method Technical Guide
📖 Scope and Summary of the Standard
The ASTM D6239-09 (Reapproved 2015) standard specifies a test method for the determination of total soluble uranium activity in drinking water using high-resolution alpha-liquid-scintillation spectrometry. This method is validated for measuring uranium activities at levels of 0.037 Bq/L (1 pCi/L) or greater, establishing it as a highly sensitive approach for drinking water analysis and compliance monitoring. The methodology aligns with fundamental practices for water sampling (D3370), radioactivity measurement (D3648), and instrument quality control (D7282) to ensure a robust analytical framework.
⚠️ Safety Considerations: This standard does not purport to address all safety concerns. Users must consult Section 9 of the standard for specific hazard statements regarding chemical reagents and extraction procedures. Establishing appropriate safety practices is the responsibility of the user.
A distinct advantage of this method is the energy resolution achievable (~250 keV FWHM for ²³⁸U at 4.2 MeV). This allows for the estimation of the ²³⁸U to ²³⁴U activity ratio, which can indicate the solubility and geochemical origin of uranium in the water source. The values stated in SI units are regarded as standard in the test method.
⚙️ Test Procedure and Key Parameters
The analysis begins with a 200 mL acidified water sample spiked with a known activity of ²³²U as an isotopic yield tracer. The sample is boiled briefly to remove radon gas and evaporated to a volume of less than 50 mL. The chemical recovery is enhanced by adjusting the solution to approximately 0.01 M diethylenetriaminepentaacetic acid (DTPA) and carefully setting the pH between 2.5 and 3.0.
The sample is equilibrated with 1.50