An old glass jar inside a beaten up old safe at the bottom of a waste pit may seem an unlikely place to find a pivotal piece of 20th century history. But that's just where the first batch of weapons-grade plutonium ever made has been found - abandoned at the world's oldest nuclear processing site.
     The potentially dangerous find was made at Hanford, Washington State, the site of a nuclear reservation, established in 1943 to support the US's pioneering nuclear weapons program.
     Hanford made the plutonium-239 for Trinity, the first ever nuclear weapon test, on 16 July 1945. Just three weeks later, more Hanford plutonium was used in the nuclear strikes on the Japanese cities of Hiroshima and Nagasaki.
     But sloppy work by the contractors running the site saw all kinds of chemical and radioactive waste indiscriminately buried in pits underground over the 40 years Hanford was operational, earning it the accolade of the dirtiest place on Earth.

Nuclear archaeology
     In 2004, clean-up work uncovered a battered, rusted, and broken old safe containing a glass jug inside which was 400 millilitres of plutonium (voir Note !)
     Recent tests by Jon Schwantes' team at the Pacific Northwest National Laboratory in Richland, Washington, has shown this plutonium was the first ever processed at the site, and the first made on a usable scale anywhere in the world.
     Schwantes and colleagues used the fact that plutonium naturally decays to uranium to date the sample to 1946, give or take 4.5 years, by comparing the amounts of the two metals present inside the jug. Its age allowed the team to establish that the plutonium must have come from one of four reactors - out of 11 in the US at the time - from which fuel was reprocessed into plutonium.
     Three of those reactors were on the Hanford site, with the fourth at Oak Ridge in Tennessee. Comparing the minor plutonium isotopes in the sample to signatures for each of the four reactors showed that the sample came from the X-10 reactor at Oak Ridge.

Historical find
     But only trawling through records at Hanford helped Schwantes and his team realise the historical significance of their find. The Hanford site's reprocessing plant, the first in the world, was completed before the reactors nearby were ready, in late 1944. So the inaugural run of the reprocessor on 9 December 1944 used fuel shipped from Oak Ridge.
     "The very next run [and all subsequent runs] used Hanford plutonium," says Schwantes. "We have the oldest known sample of plutonium-239 - weapons plutonium."
     His team read that a safe matching the description of the one unearthed in 2004 was sealed in 1945 because of radioactive contamination. It was disposed of in 1951, and remained lost for the next 50 years.
     "The contamination was not from the plutonium jug," Schwantes says. "The jug was intact when found."
     Plutonium-239 has a half-life of 24,110 years and emits alpha particles that are too bulky to penetrate even skin or paper. It is most dangerous when inhaled as a dry powder, where its decay in the lungs can cause cancer, he adds.

Bomb mystery
     John Simpson, an expert on nuclear history at Southampton University in the UK, thinks the new find is important.
     "From the historical records, it looks as if they've got it right," he says. "But the puzzling thing is, why didn't this plutonium make it into the bomb?" In 1944, the Americans were working flat out to develop a nuclear capability - it's strange that any first large batch of plutonium-239 should be stored and not used, he says.
     Schwantes thinks that is because of the radioactive contamination to the safe it was being stored in. The first batch would eventually have been folded back into the stockpile if not for that contamination.
     But despite its historic significance, Schwantes doesn't plan to put the sample in a museum. He is working with New Brunswick Labs to create a standard reference sample for plutonium-239 from the material, partly because of it's primacy as the oldest sample. "The other factor is its extreme purity - 99.96% plutonium-239 is as pure a sample of 239 I have seen produced from any reactor," says Schwantes.
 
 
 

Journal reference: Analytical Chemistry (DOI: 10.1021/ac802286a)

See a gallery of images of the find and where it came from

World's oldest weapons-grade plutonium found in a ditch
     Plutonium-239 found inside a broken, rusty safe has been shown to be of historic significance: dating from December 1944 it is the very first weapons-grade plutonium refined at the site, or anywhere in the world.
     The find was made at the Hanford Site, Washington State, which supplied the US nuclear weapon program from its beginnings until the 1980s. The site is dangerously contaminated by radioactive waste indiscriminately buried underground over years.