REFERENCE MATERIALS FOR TRACE ACTINIDE CONTENT IN PLUTONIUM OXIDE
Richard Essex, Lav Tandon, Cole Hexel, Amy Gaffney
Nuclear forensic analyses of plutonium (Pu) materials encountered outside nuclear safeguards control can include chemical composition, isotopic composition, and the concentration of various contaminants. Results from these measurements provide insights into how and when the Pu was produced and help place limits on potential uses and provenance of the material. As part of a program to enhance nuclear forensic analytical capabilities, the United States Department of Homeland Security sponsored the development of nuclear forensic reference materials, including plutonium oxides, NFRM Pu-1 and NFRM Pu-2. These were prepared and characterized for americium (Am), neptunium (Np) and uranium (U) occurring as trace constituents in Pu. The starting material for these reference materials were an oxidized Pu metal (NFRM Pu-1) and a Pu oxalate precipitate (NFRM Pu-2). Both were calcined (≤ 750 °C) and then dispensed to individual sample units comprised of 200 mg of oxide in robust quartz glass vials. Characterization was performed on randomly selected units by controlled potential coulometry for Pu assay and thermal ionization mass spectrometry (TIMS) for isotopic composition. Characterization of Am mass fractions was performed by isotope dilution mass spectrometry (IDMS). Np mass fractions were measured by externally calibrated inductively couple plasma mass spectrometry (ICP-MS). U mass fraction measurements were by IDMS and isotopic composition analyses were by TIMS. Characterized attributes are provided for a reference date of 01 January 2019. Both materials have a Pu-239 isotope amount fraction of greater than 93% and are nominally PuO2 with a Pu mass fraction of approximately 0.88 g g-1. Mass fractions of trace actinide constituents range from 800 µg g-1 for Am to 30 µg g-1 for Np. The trace constituents are homogenously distributed within the Pu oxide material. Monoisotopic Am-241 is consistent with ingrowth from decay of Pu-241. U-234, U-235, and U-236 are primarily ingrown from decay of Pu isotopes but a significant proportion of measured U-238 appears to be due to process related contamination of the Pu oxide or analysis blank. Monoisotopic Np-237 also appears be a combination of ingrowth from Am-241 since purification and a homogenously distributed contaminant in the Pu oxide.
Proceeding of the 2021 INMM/ESARDA combined meeting
, Tandon, L.
, Hexel, C.
and Gaffney, A.
REFERENCE MATERIALS FOR TRACE ACTINIDE CONTENT IN PLUTONIUM OXIDE, Proceeding of the 2021 INMM/ESARDA combined meeting, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=932996
(Accessed February 23, 2024)