Scientists looking for ways to determine the sources of illicit nuclear materials have applied a method better known to geologists to try to prove that small blocks of uranium are relics of Nazi Germany’s nuclear weapons program.
During World War II, Nazi scientists racing to beat the US to the development of the bomb refined tonnes of ore into 1200 uranium-metal cubes, each about five centimeters wide and weighing 2.2 to 2.5 kilograms.
The Germans then attempted to use them to build reactors from which to generate plutonium, says Jon Schwantes, a nuclear radiochemist at the Pacific Northwest National Laboratory in the US.
Late in the war, Schwantes says, a US/UK special forces team managed to locate and capture at least 600 of the cubes. The fate of the others is unknown. Only a handful of those 600 captured cubes still exist; the rest were probably utilised as a convenient source of uranium.
But even the few cubes that remain might be fakes. Uranium, yes. Nazi uranium? Schwantes says that for years, people thought they were from the Nazis’ nuclear program, but nobody was sure – even about a cube in the Smithsonian Museum in Washington, DC.
To figure out if they were real, Schwantes’ team turned to radiochronometry, the science geologists and geophysicists use to date rock strata.
Read more: The hunt for WWII German uranium
It works by comparing the amount of uranium to its decay products, using these ratios to determine how long it has been since the rock – or, in this case, the uranium cube – was formed. In the case of ancient rocks, this involves the use of very slow radioactive decay chains, but for the Nazi cubes the team turned to different and more rapid radioactive decay chains, such as the decay of uranium-235 to a rare and unstable element known as protactinium.
To date, the tests aren’t definitive.
“We have preliminary results on two of the cubes,” says Schwantes. “That age is consistent with Nazi-era cubes, although the results at this point are still preliminary.”
At the moment, the best his team can do is determine the age of the cubes to within a few years. But he thinks it’s possible to refine the method well enough to pinpoint their ages to within a few months. If so, he says, that will not only be good enough to confirm the pedigree of these cubes to Nazi Germany, but also determine which of two labs they came from, because the labs were producing cubes in different years.
All of which is great fun for historians, but ultimately there is a sobering side, because these cubes were created for a terrifying purpose. “I’m glad the Nazi program wasn’t as advanced as they wanted it to be,” says Schwantes’ colleague Brittany Robertson. “Otherwise, the world would be a very different place.”
The research was presented today at the autumn meeting of the American Chemical Society.