ASTM C1931-23 - Standard Test Method for Determination of Uranium Isotopic Composition by Gamma-Ray Spectrometry

1.1 This test method applies to the nondestructive determination of the isotopic abundances of uranium, typically ²³⁴U, ²³⁵U, ²³⁶U, and ²³⁸U, in isotopically homogeneous uranium-bearing materials using gamma spectrometry. The material is commonly inside a container and is measured without specimen preparation.

1.2 This test method is applicable to items containing sub-gram quantities of uranium to the maximum uranium mass allowed by criticality considerations.

1.3 Measurable gamma ray emissions from uranium cover the energy range from below 80 keV to above 1000 keV. K-X-ray emissions from the isotopes of uranium and their daughters are found in the energy region around 100 keV. This test method has been applied to all portions of this energy range.

1.4 The isotopic abundance of ²³⁶U is usually not directly determined because its low-energy gamma rays are too weak (1)2 to be detected under normal measurement conditions. Isotopic correlation techniques have been used to estimate its relative abundance (2).

1.5 This test method has been demonstrated in routine use for isotopic amount fraction (atom %) of ²³⁵U from 0.2 % to 97 %.

1.6 This test method requires decay equilibrium (160 days for 99 %) between ²³⁸U and its 24.1 d half-life ²³⁴Th daughter. Corrections can be made if the date of chemical separation of the ²³⁴Th daughter is known.

1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.9 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.