Production of highly-enriched ¹³⁴Ba for a reference material for isotope dilution mass spectrometry measurements

Isotope dilution mass spectrometry (IDMS) is an analytical technique capable of providing accurate and precise quantitation of trace isotope abundance and assay providing measurement uncertainties below 1 %. To achieve these low uncertainties, the IDMS method ideally utilizes chemically pure “spike” solutions that consist of a single highly enriched isotope that is well-characterized relating to the abundance of companion isotopes and concentration in solution. To address a current demand for accurate ¹³⁷Cs/¹³⁷Ba ratio measurements for “age” determination of radioactive ¹³⁷Cs sources, Idaho National Laboratory (INL) is producing enriched ¹³⁴Ba isotopes that are tobe used for IDMS spikes to accurately determine ¹³⁷Ba accumulation from the decay of ¹³⁷Cs. The final objective of this work it to provide a homogenous set of reference materials that the National Institute of Standards and Technology can certify as standard reference materials used for IDMS. The process that was developed at INL for the separation and isolation of Ba isotopes, chemical purification of the isotopes in solution, and the encapsulation of the materials will be described.