Using Nuclear Materials To Prevent Nuclear Proliferation.

International efforts to halt proliferation of nuclear weapons are threatened by the vulnerability of weapons-usable material to theft and smuggling especially in Russia1,2,3. Highly-enriched uranium (HEU) is difficult to detect and the origin of stolen HEU or plutonium is often hard to determine after recovery. Here we show that mixing 232U into HEU makes it observable with low-cost radiation monitors. Adding a proportion of 233U which is associated with a specific storage site to HEU enables attribution to be performed on stolen HEU that has been recovered. Incorporating 244Pu into plutonium solves the same attribution problem for this material. Existing and planned US efforts for radioactive surplus disposition could provide a source for the tags4. Current US-Russian programs to dispose of surplus nuclear weapons open opportunities to incorporate tags in large (but not all) amounts of weapons-usable material.5 This method could be applied to civilian reprocessing of spent fuel to prevent proliferation.6 Finally, radiation monitors are routinely used to detect smuggling across borders and the tags enhance those detection capabilities for HEU.