Qualification and initial characterization of a high-purity 233U spike for use in uranium analyses

• A high-purity 233U material is identified as a source material for uranium isotopic standards.
• The material is of higher purity than CRM 111-A which is currently being used as a spike for IDMS.
• Two TIMS analytical techniques (i) total evaporation technique and (ii) conventional analysis using the TRITON instrument are employed for the characterization.
• The bias due to peak-tailing is estimated to be ∼2 ppm at 234U and ∼0.5 ppm at 235U and 236U.

Several high-purity 233U items potentially useful as isotope dilution mass spectrometry standards for safeguards, non-proliferation, and nuclear forensics measurements are identified and rescued from downblending. By preserving the supply of 233U materials of different pedigree for use as source materials for certified reference materials (CRMs), it is ensured that the safeguards community has high quality uranium isotopic standards required for calibration of the analytical instruments. One of the items identified as a source material for a high-purity CRM is characterized for the uranium isotope-amount ratios using thermal ionization mass spectrometry (TIMS). Additional verification measurements on this material using quadrupole inductively coupled plasma mass spectrometry (ICPMS) are also performed. The comparison of the ICPMS uranium isotope-amount ratios with the TIMS data, with much smaller uncertainties, validated the ICPMS measurement practices. ICPMS is proposed for the initial screening of the purity of items in the rescue campaign.

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