Measurement of the 231 Pa/ 235 U ratio for the age determination of uranium materials.

The paper describes the age (production date) determination of uranium reference materials using the 231 Pa/235 U ratio. Direct addition of 237 Np in secular equilibrium with its 233 Pa daughter was chosen instead of the regular milking of 237 Np to avoid possible loss of Pa. Sample preparation consists of a fast, one-step procedure. The developed method using ICP-MS for the measurement of 231 Pa is more precise than alpha spectrometry and is applicable for freshly produced low-enriched uranium materials. The measured ages are in good agreement with the reported production dates, thus the 231 Pa/235 U chronometer can be applied for validation of 230 Th/234 U in nuclear forensics and safeguards.