Rare capabilities at the Department of Energy's Pacific Northwest National Laboratory are being enlisted in the fight to prevent threats from those who might steal nuclear material.
Plutonium in weapons usable forms can be produced through various processes. By replicating some of these different conversion processes in a specialized research facility, nuclear scientists can then characterize subtle differences in the resulting material. The differences, called signatures, are a due to the varied means of processing plutonium and can be used by the government to trace the material to where it was produced.
After analyzing small samples, PNNL will create a database of signatures related to each process for the Department of Homeland Security's Domestic Nuclear Detection Office. The U.S. could then use the database to use to evaluate any plutonium that may be confiscated from smugglers.
More information is available in this DHS blog post.