Identifying Uranium Cubes From Nazi Germany’s Nuclear Program

Researchers are working to determine the origins and whereabouts of hundreds of these cubes.

Hundreds of uranium cubes from Nazi Germany’s disrupted nuclear program were lost after World War II, and researchers are developing methods to identify them when they turn up.

American researchers are reporting that new detection methods can confirm the origin of cubes of uranium that Nazi physicists and chemists devised in their race to make Germany a nuclear power. The United States was also relying on German scientists, many of whom fled Nazism’s genocide of the Jewish people, to successfully produce the atomic bombs that were dropped on Japan.

These detection methods can aide law enforcement, military and border officials to detect smuggled fissionable materials, according to a press release from the American Chemical Society (ACS).

At the ACS fall 2021 meeting, scientists will present their findings virtually and in-person. The meeting features more than 7,000 presentations on a wide range of scientific topics.

Nazi scientists produced hundreds of uranium cubes, each measuring about 2 inches on each side, for ultimately unsuccessful experiments. At the end of the war, American and British troops seized the cubes. And the mystery starts there.

While most of the cubes are believed to be in the U.S. or Europe, the fate of many of the uranium cubes is unknown. The Pacific Northwest National Laboratory (PNNL) in Washington State has one, but no one knows how it arrived there.

“We don’t know for a fact that the cubes are from the German program, so first we want to establish that,” said the project’s principal investigator, Jon Schwantes. “Then we want to compare the different cubes to see if we can classify them according to the particular research group that created them.”

PNNL uses the so-called Heisenberg cube, which based on anecdotal evidence came from the Nazi lab directed by physicist Werner Heisenberg in Berlin.

German theoretical physicist Werner Karl Heisenberg (1901–1976) won the 1933 Nobel Prize for physics. (Keystone/Getty Images)

“We didn’t have any actual measurements to back up that claim,” said PNNL researcher Brittany Roberson.

Robertson, a doctoral student, modified certain analytical techniques and combined them with Schwantes’ forensic methods to determine the cube’s origins. She used radiochronometry, a technique used by nuclear physicists that resembles the geological technique that determines the age of rocks based on radioactive isotope content.

In the early 1940s, Nazi scientists sought to use nuclear fission to produce plutonium from uranium for the war effort. Heisenberg’s group started in Berlin and later moved to Haigerloch to avoid Allied troops. Under Kurt Diebner, another team was located at Gottow.

Both groups produced the cubes to fuel nuclear reactors. These were hung ocables submerged in “heavy” water, in which deuterium replaces lighter hydrogen. This was in the hope that the radioactive decay of the uranium would unleash a self-sustaining nuclear chain reaction.

In the first case, the cubes consisted of fairly pure uranium metal, but over time, radioactive decay transformed some of it into thorium and protactinium. Robertson is adapting the radiochronometry procedure to better separate and quantify these elements in PNNL’s cube. This should reveal when the cube was made.

She is also refining this method to analyze rare-earth element impurities in the cube, thus possibly revealing where the original uranium was mined. This could show whether it was from the Heisenberg or Diebner group.

Robertson and Schwantes are working with Carlos Fraga of PNNL to test the coatings the Germans applied to limit oxidation of the cubes. They recently discovered that a cube held at the University of Maryland is unexpectedly coated with styrene. The team thus learned that Diebner’s lab shared cubes with Heisenberg, who needed more fuel for his reactor.

“We’re curious if this particular cube was one of the ones associated with both research programs,” Schwantes said. “Also, this is an opportunity for us to test our science before we apply it in an actual nuclear forensic investigation.”

Before Germany could succeed in producing an atomic weapon, Allied forces swept into Germany and confiscated some cubes of uranium intended as fuel. Some Heisenberg cubes at Haigerloch were seized in 1945, and more than 600 were shipped to the U.S.

“I’m glad the Nazi program wasn’t as advanced as they wanted it to be by the end of the war, because otherwise, the world would be a very different place,” Robertson said.

Some of the cubes may have been used in the U.S. nuclear weapons effort, resulting in the atomic mushroom clouds over Hiroshima and Nagasaki, Japan later that year.

While some cubes are located at PNNL and other sites, and in the hands of collectors, no one knows the whereabouts of hundreds of others, including hundreds of so-called Diebner cubes.

Edited by Judith Isacoff and Kristen Butler