Historically, mass spectrometry methods have been used to characterize nuclear and radiological materials for a number of applications. The predominant focus of these analyses has been the high precision and accuracy determination of isotopic composition and concentration. More recently these methods have been used to support nuclear forensics investigations. While classical isotopic composition and concentration measurements continue to be critical in this emerging field, the ability to determine the time since creation or purification, the “model” age, has grown in significance for nuclear materials. The method used to determine model age, radiochronometry, is based upon the ability to measure the in-growth of a radiogenic decay product, the daughter or grand-daughter, from a parent isotope which exists as part of the material’s predominant matrix. The accurate determination of a material’s age assumes both the complete removal of the daughter or grand-daughter isotope from the parent at the time of purification and that the radiochronometry system has remained closed with no introduction of parent or progeny isotopes since purification. Unfortunately, these assumptions are often not valid, resulting in a model age determination that differs from the production date of the material. In these cases, the calculated model age often indicates an older separation date. For this reason, model age determination using multiple radiochronometers is ideal. Concordance of model ages determined using multiple radiochronometry pairs increases confidence in a material’s age, while discordance may provide insight into the processes used to purify a particular material. The relatively recent interest in radiochronometry of materials from the nuclear age as a tool to support nuclear forensics investigations has resulted in the need for reference materials that have been certified for age. Development of new certified reference materials and tracers is ongoing but requires significant effort. This presentation will discuss the concepts associated with model age determination of nuclear materials along with isotope dilution tracer calibration and results from radiochemistry sample preparation and mass spectrometry measurement of recently analyzed nuclear samples.

Radiochronometry methods to support nuclear forensics investigations

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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