Researchers Work on Mystery Uranium Cubes to Better Understand Nazi Progress on Atomic Bomb

As the Allies pushed into Nazi Germany in April 1945, a special team hunted for the Third Reich’s nuclear weapons program and famed physicist Werner Heisenberg.

In the town of Haigerloch, hidden in a cave beneath a castle, the Allied team uncovered an experimental nuclear reactor and buried in a field nearby, 659 uranium cubes. Heisenberg fled into the night, riding a bicycle with a backpack full of the radioactive blocks.

Most of the so-called “Heisenberg cubes” were lost after the war. Researchers in the US are now, for the first time, carrying out nuclear forensic analysis on three uranium cubes believed to be from Nazi laboratories, in a project that could have historical significance, as well as implications for nuclear security.

Brittany Robertson and Jon Schwantes of the Pacific Northwest National Laboratory in Washington State revealed the project on Tuesday at a meeting of the American Chemical Society.

“It’s somewhat surreal and somewhat intimidating,” Robertson said of working with an item likely handled by the famous Nazi scientist Heisenberg. “We’re dealing with these historical artifacts that are in limited quantity and we’ve got to get as much information as possible off of a very tiny amount of material.”

The artifacts’ Nazi origin “has been claimed by a number of people that have had access to these cubes, but to our knowledge, never actually confirmed experimentally,” she said. Robertson is pioneering new techniques to determine the material’s origin, as part of her doctoral thesis.

Her new forensic methods could “enhance the capabilities of the nuclear forensic community in important ways,” Schwantes said.

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The US and Nazi Germany were both racing to develop nuclear technology during the war. The Germans had a head start, with several teams competing to develop nuclear fission with the end goal of developing a weapon. Heisenberg’s group worked out of Berlin, before moving to Haigerloch in southwest Germany to evade Allied troops, while scientist Kurt Diebner headed a research group in Gottow.

Between the two facilities, the Nazis amassed between 1,000-1,200 uranium cubes. The blocks are about two inches long on each side, are charcoal-gray and weigh about five pounds. The Germans suspended hundreds of them on cables in heavy water as part of a failed attempt to produce plutonium.