The date on which a radioactive source material was last separated from its decay daughters is a useful parameter in deducing the material's origins and history for nuclear forensics investigations. Age dating a 90Sr source requires accurate determination of the 90Zr daughter and the residual 90Sr parent in a sample of the source material so a time of decay can be calculated using the isotope's half-life. Because the target nuclides are isobaric, chemical separation of zirconium from strontium is required for mass spectrometric determination of the isotope amounts. Adding known amounts of low-abundance Sr and Zr isotopes prior to processing a sample and using the technique of isotope dilution (ID) permits accurate measurement of the 90Sr and 90Zr isotopes irrespective of chemical recovery. This presentation describes our application of an isotope-dilution method for determining 90Zr and 90Sr in a 90Sr source material spiked with 86Sr and 92Zr. A miniature gas pressurized extraction chromatography (GPEC) system with a column containing Eichrom Sr ResinTM was used for the separation. Zirconium was rinsed through the column with 3M HNO3 /trace HF and strontium was eluted with 1% acetic acid. Two mass spectrometric techniques, inductively coupled plasma mass spectrometry (ICP-MS) and thermal ionization mass spectrometry (TIMS), were used for measuring isotope ratios. Data were obtained with carefully prepared mixtures of non-radioactive strontium and zirconium and with 90Sr from a blood-irradiator source dissolved by Idaho National Laboratory. Measured 90Zr/90Sr ratios and corresponding ages determined by ID-ICP-MS and ID-TIMS are presented.

TIMS vs. ICP-MS measurements for age dating <sup>90</sup>Sr

245th National Meeting (2013)

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TIMS vs. ICP-MS measurements for age dating 90Sr

TIMS vs. ICP-MS measurements for age dating ⁹⁰Sr