Determining the age and origins of nuclear materials for nuclear forensics investigations
with Dr. Chistine Yifeng Chen, Postdoctoral Researcher, Cosmochemical and Isotopic Signatures Group, Nuclear and Chemical Sciences Division, Lawrence Livermore National Laboratory.
Nuclear materials such as plutonium and highly enriched uranium are highly regulated and illegal to possess outside of governmental or laboratory control in most parts of the world. When such materials are found outside of these highly regulated environments, questions surrounding their source are of immediate concern, especially if connections with trafficking or malicious use are suspected. In this context, the material's production date or "age" is a key forensic signature. The parent-daughter isotope pairs 230Th-234U and 231Pa-235U are the most common chronometers for uranium-rich materials, but in some cases, the application of both chronometers on the same sample material has yielded repeatably different or "discordant" ages, complicating their interpretation for forensics contexts. In this presentation, I describe the results of a multi-laboratory investigation of radiochronometric discordance on a suite of uranium metal and alloy samples cast under known conditions. We find that discordance is explained by chronometers preserving different events along a complex sample's production history: 231Pa-235U ages may preserve information about the feedstock material of a cast metal or alloy, while 230Th-234U ages record the timing of casting. Thus, discordance can instead enhance rather than diminish the utility of multiple chronometers. As yet, no other geochemical signature alone has demonstrated a parallel ability to temporally constrain multiple aspects of a sample's production history.
The Earth Science Colloquium Series, sponsored by Lamont-Doherty Earth Observatory and Columbia University Department of Earth and Environmental Sciences (DEES), provides a lively forum for discussing a wide variety of topics within the Earth sciences and related fields. Colloquia are attended by the full range of scientific and technical staff at LDEO. Colloquium attendance is required of all pre-orals DEES graduate students. The Colloquium Series supports the Lamont Seminar Diversity Initiative.