How experts traced the explosive materials to Russia

A CSI-style probe uncovered a distinctive radioactive signature.

A detailed 2013 report on the Bulgarian case from Lawrence Livermore National Laboratory explained how a nine-month study by a team of lab scientists discerned telltale particle shapes and sizes as well as distinctive radioactive decay rates and concentrations of 72 different elements in the sample provided to Washington, eventually leading “investigators to the source of the HEU [highly-enriched uranium].”

The lab analyzed the fiber content of the container’s labels, with results showing they were “most plausibly produced in Eastern Europe,” while the concentration of certain radioactive particles pointed toward production in “the former Soviet Union” and probably a light-water reactor, such as  a facility associated with the production of fuel for “naval propulsion systems,” according to the Livermore report.

Mark Kristo, a chemist at Livermore, said in an interview this conclusion was partly based on the type of lead in the surrounding canister, and the presence of a colorant known as barium chromate – a carcinogen banned in the West -- in its wax lining. The Russians, he said, did not want to look at the paper, glass, and lead.

French researchers, separately writing in a 2007 International Atomic Energy Agency report, said, the analysis of the Paris sample “gave a good correlation with the…enriched light water reactor fuel reprocessing” – of the type that current and former U.S. officials say was done in the early 1990’s at Mayak. “This sample really looks like the one in the Bulgarian case,” the French researchers added. – R. Jeffrey Smith and Douglas Birch