Nuclear forensics methodology identifies legacy plutonium from the Manhattan Project

The X-10 nuclear reactor was built at the Clinton Engineering Works in Oak Ridge, Tennessee, USA, as the world’s first Pu production reactor. Operation commenced in November 1943, producing Pu on the gram-scale for the first time. A 61.1 mg sample of 239Pu has been identified at Los Alamos National Laboratory containing multiple forensic signatures consistent with production from the X-10 reactor in early 1944, when the first samples of reactor-produced Pu were shipped from X-10 to Los Alamos. Our nuclear forensics investigation included Pu isotopic analysis, chronometry, X-10 reactor physics simulations, and trace metal analyses. This historic sample has been determined to be among the oldest reactor-produced Pu reported in the literature and is among the first 1.4 kg of Pu ever produced.