In order to properly characterize nuclear waste and perform nuclear forensics, we use an array of chemical tools. One critical tool is isotope ratio determination, in which uranium (U) and plutonium (Pu) isotopes are measured and compared to known nuclear materials. Actinide isotope ratios (such as the ratios of 234, 235 and 236 to 238 for uranium and 240 and 242 to 239 for plutonium) can provide evidence for the source and enrichment of nuclear materials. While U and Pu isotopes are radioactive, the isotopes listed above decay relatively slowly with half-lives in the thousands to billions of years. The slow decay of these isotopes allows us to treat these isotope ratios as effectively stable (under short timescales) whereas measuring short-lived isotopes, such as 238Pu and 241Pu, can provide information on radioactive decay of nuclear material.
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