In search of lost uranium cubes from Germany

In 2013, Timothy Koeth, an associate professor of research at the University of Maryland, received a rather extraordinary birthday gift: a small cloth lunch bag containing a small object wrapped in brown paper towels. As Koeth removed the diapers, his eyes widened in astonishment. He immediately asked, "Where did you get that?"

Inside, he found a heavy metal cube and a crumpled message, a provocative note wrapped around a stone that was crumbling through the window of history. It read: "From Germany, from the nuclear reactor that Hitler tried to build, Don of Ninninger."

Koeth's friend smiled, picked up the 5-pound block of uranium metal and handed it to him. Although small in size, the cube was heavy, dense and steeped in lost history. Koeth accepted the cube and its note as an invitation to the adventure of a lifetime.

In the May 2019 issue of Physics today, Koeth and Miriam Hiebert, a PhD student working with him on this project at the A. James Clark School of Engineering at UMD, describe what they discovered while exploring the German quest and the failure of the construction of a nuclear reactor during World War II.

Uranium is weakly radioactive and this cube measures approximately 2 inches on each side. "It's surprisingly heavy, given its size, and it's always fun to watch people's reaction when they detect it for the first time," Hiebert said.

A chandelier of nuclear elements

This cube represents one of the 664 components of uranium metal that have been assembled in a shape reminiscent of a chandelier and constituting the core of the nuclear reactor experiment that a team of German scientists has attempted to build. towards the end of the Second World War, including Werner Heisenberg. – a theoretical physicist and one of the leading visionaries of quantum mechanics. The chandelier was immersed in heavy water to regulate the fission rate.

The experimental laboratory of the Germans was small and underground in the city of Haigerloch. It is now the Atomkeller museum, which the public can visit. "This experiment was their last and closest attempt to create an autonomous nuclear reactor, but there was not enough uranium present in the heart to achieve that goal," Koeth said. .

One of the most surprising things that Koeth and Hiebert have discovered up to here is that, if the 664 cubes of uranium at Haigerloch were not enough to build a standalone reactor, 400 cubes more were in Germany at the time.

"If the Germans had pooled their resources rather than keeping them divided between separate and rival experiences, they might have built a functioning nuclear reactor," Hiebert said. "This may highlight the biggest difference between the German and American nuclear research programs.The German program was divided and competitive, while under the leadership of General Leslie Groves, the US Manhattan project was centralized and collaborative. "

How close were the Germans?

How far did the Germans get close to a running nuclear reactor? It is difficult to answer this question, but "it was calculated that the Haigerloch reactor experiment would have required about 50% more uranium to run," Koeth said. "Even if the 400 additional cubes had been brought to Haigerloch for use in this reactor experiment, German scientists would still need more heavy water to run the reactor." Although the reactor is the cradle of the Nuclear physics and At the beginning of the American efforts, there was no imminent threat of a nuclear Germany at the end of the war ".

Another important aspect of Koeth and Hiebert's work is an effort to trace the recovered cubes of Haigerloch that were eventually shipped to the United States. "The cubes were distributed to various people across the country," said Hiebert. "We do not know how much has been distributed or what has happened to others, but there are probably more hidden cubes in basements and offices across the country, and we would like to find them!"

Among the many questions that remain unanswered, the main ones are: how many of these cubes still exist and what happened to them?

"We hope to talk to as many people as possible who have been in contact with these cubes," said Hiebert. "We have learned a lot about our cube and others, but we still do not know exactly how it ended up in Maryland, 70 years after it was captured by Allied forces in the south. l & # 39; Germany. "

Koeth and Hiebert also try to find out more about the 400 other cubes that found themselves on the black market in Europe after the war.

Among the many questions that remain unanswered, the main ones are: how many of these cubes still exist and what happened to them? Physics today helped to track down some; For more information, see https://physicstoday.scitation.org/do/10.1063/PT.6.4.20190501a/full/.

The article titled "Tracking the Journey of a Uranium Cube" by Timothy Koeth and Miriam Hiebert appears in the May 2019 issue of Physics today.