One of the tiny gray cubes would not raise eyebrows on a desk. They look almost like paperweights to the untrained eye.
Marie Curie's grand-daughter has one. Miriam Hiebert, an historian and materials scientist, said that she uses it as a doorstop.
Although the objects are only 2 inches (5 cm), their weight is approximately 5 pounds (2kg). They're made from the most heavy element on Earth, uranium.
These cubes were part of the experimental nuclear reactors that Nazis built during World War II. Researchers have found that only 14 of the more than 1000 cubes used in Nazi Germany's nuclear weapon experiments are still in existence.
In the 40s, over 600 cubes were captured and returned to the USA. However, it is not clear what happened to the majority of the cubes after this.
Timothy Koeth and Hiebert, both professors of material science at the University of Maryland are currently writing a book on the cubes. They told Insider that they believe they have the right answer after years of research.
Miriam Hiebert, Timothy Koeth (John T. Consoli/UMD).
Cubes of small size with a long history
Koeth refers to the cubes "the only living remnant" of Nazi Germany’s nuclear effort.
He said, "They are the motivation of the whole Manhattan project."
Germany was the world's leader in physics and nuclear energy science in the years leading up to war. Otto Hahn, a German chemist, revealed in 1938 that he had created fission using neutrons aimed at a uranium-core.
Enrico Fermi and Albert Einstein, two of the scientists who fled Europe, warned the USA that Germany might develop an atomic bomb. The arms race began.
Uranium in its natural state is not radioactive. The cubes are not very dangerous. Apply a neutron to the uranium, specifically U-235, and it will crack open "like a piata," Koeth said.
He said, "You smash it open using a neutron, new elements and also more neutrons"
An explosion can only be created when there is a chain reaction. The neutron is captured by another uranium-atom which then splits open creating more neutrons. The neutrons must be slowed by a substance called moderator to make this possible.
This was possible because graphite was used by the US. In December 1942, scientists with the Manhattan Project developed a self-sustaining nuclear chain react in which they could sustain themselves. Kurt Diebner and Werner Heisenberg, the nuclear program leaders in Nazi Germany, chose heavy water to be their moderator. Heavy water is water in which hydrogen atoms have been replaced by deuterium. The water would then be dipped in uranium cubes.
Two prototype reactors were built by the Nazis. The larger one had 664 uranium spheres suspended from a plate and suspended above a pit of heavy liquid. The smaller reactor had 400 cubes.
The "Alsos” mission
The Allied forces did not know how far the Nazi nuclear program was. They were also nervous.
In 1943, the Allies launched an undercover mission codenamed "Alsos" in order to find out. An estimated dozen soldiers, scientists, interpreters and scientists traveled across Europe in search of evidence of Nazi nuclear experiments. As the war was nearing its end, the mission's goal changed to ensure that no nuclear material or scientists made it into the hands the Soviets.
About 1.6 tonnes of uranium cubes were captured by the Allies in south Germany in April 1945. Heisenberg and his team as well as the larger of Germany's reactors, neither of which had ever worked, were hiding there. Nearly all of the cubes were returned to the USA. The smaller reactor was not found by the Alsos mission.
After locating German Uranium Cubes in Haigerloch, Germany, Alsos intelligence officers. (Samuel Goudsmit/AIP Emilio Segr Visual Archives)
The pile was emptied of the cubes.
Hiebert stated that the trail of the cubes became cold after they arrived in the US. Because the US kept its nuclear program secret, there aren’t many public records on Nazi uranium.
She said that 14 of the nearly 1,000 known exist, so most of them are not yet accounted for.
These 14 clues offer some insight into what might have happened to the others.
Koeth has two of the 14. He has been a keen collector of nuclear items since his teens. They were both given to Koeth by colleagues. The first gift was given to him by colleagues around ten years ago. However, the anonymous giver requested that he remain anonymous so Koeth will not reveal how they obtained the cube.
The handwritten note included the following: "Taken form Germany from the nuclear reactor Hitler tried building. Gift of Ninninger
Koeth's cube was accompanied by a note. (Timothy Koeth).
Robert D. Nininger (his name only has one n) was, as it turns out, a geologist working for the US Atomic Energy Commission during the 1950s. Koeth found documents that prove he was involved in the Manhattan Project. The difficult task of finding uranium was a challenge for the geologists involved in the project.
Hiebert stated that "just figuring out where it was from was a huge challenge."
Koeth received the other cube from Dick Duffey, a former University of Maryland faculty member. Koeth stated that Duffey was a chemical engineer who had worked in a Beverly plant that processed scrapuranium during World War II.
These findings, and others, lead Hiebert to believe that most of the Nazi-cubes that made their way to America were reused and used in America’s nuclear program. Some, however, were "picked from the pile" and kept for souvenirs.
Hiebert, Koeth and others found documents that suggested the 400 cubes were sold to the USSR on the black market.
From a nuclear reactor to counter-proliferation efforts
Although the Pacific Northwest National Laboratory has another Nazi cube, it doesn't have any records about its history.
Brittany Robertson and Jon Schwantes, two of the scientists involved, have recently developed a method to date the cube, and other uranium products, more accurately than ever before. They measured two atoms, protactinium, and thorium that accumulate as uranium degrades over time.
Robertson and Schwantes presented their findings at the American Chemical Society's annual meeting last month. The results showed that the cube was in the age range expected. This is the same time period as Nazi Germany was creating nuclear weapons.
Insider reports that the cube's primary function is now training.
Security personnel learn how to spot radioactive and nuclear material at a glance in the national laboratory. The cube is a great example of a training tool.
Schwantes stated, "I find that that really interesting storyline for the cube that it was originally produced for somebody’s nuclear program and now it’s being used to nuclear nonproliferation."
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