A plutonium sample recently found at a U.S. waste dump is leftover from a batch used by the Manhattan Project, which produced the world's first nuclear bomb test, a team of chemists has announced.
A nuclear waste cleanup team unearthed the 0.01 ounces (400 milligrams) sample in a waste pit at the Hanford Nuclear Reservation in Washington, where it was sealed in a glass jar and enclosed in a safe.
The discovery highlights new techniques in the emerging field of nuclear archaeology that could become key factors in nuclear deterrence.
Although the mysterious material was unearthed in 2004, its origins were unknown until the researchers used state-of-the art methods to identify its age and history.
The clues led the team to the X-10 reactor at Oak Ridge, Tennessee, which was once part of the Manhattan Project. The spent sample was sent to Hansford for reprocessing—or removing bomb-grade plutonium from nuclear waste products.
"This kind of nuclear archaeology is unclassified, so it gives the public a rare glimpse at what can be done to potentially identify the origin of these types of materials," said nuclear chemist and team member Jon Schwantes, of the Pacific Northwest National Laboratory in Richland, Washington.
(Related: "Archaeologists Explore Cold War Nuclear Test Site".)
Finding "Fingerprints"
The work, described in the journal Analytical Chemistry, highlights experts' growing ability to pinpoint the origins of dangerous nuclear materials.
Because plutonium is rare in nature, weapons-grade reactors must process uranium into the right version, or isotope, of plutonium. To find a plutonium sample's age, scientists chart the element's rate of decay back into uranium.
The levels of different plutonium isotopes then provide a unique fingerprint that can reveal the reactor of origin.
"Each reactor that's producing this material has a slightly different makeup to it," Schwantes explained. "It may be burning a different type of fuel or [running at] higher or lower burnup levels," resulting in different isotope ratios in the finished product.
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