Uranium and plutonium are the main ingredients in an atomic bomb. In 1938, German scientists discovered that they could fissure the nuclei of these unstable atoms, releasing a great deal of energy in the process. The following year, Nazi Germany’s nuclear program was born. Scientists in the country began to produce uranium cubes – which would be used in a nuclear reactor to produce plutonium – but the project was never completed.
If the photo above looks familiar, it’s because the object is the face of the Tesseract – the fictional cube that holds the jewel of infinity in Marvel’s Cinematographic Universe. But their official name is “Heisenberg’s Cube,” after the physicist who helped create them. Werner Heisenberg worked in a laboratory located under a church in the German city of Haigerloch.
In 1945, American and British troops found 664 cubes in this laboratory and shipped them to the United States. There’s only one problem: scientists currently only know the whereabouts of twelve of them. Many were likely used in American nuclear weapons, while others ended up in the hands of collectors. We don’t know how many of these cubes might be out there.
One of the known copies is in the Pacific Northwest National Laboratory (PNNL), laboratory linked to the US Department of Energy. Researchers don’t know how or when the cube got there – in fact, they’re not even sure the cube actually came from the German program. To find out, the team developed techniques to define when and where uranium was mined.
The origin of cubes
The first step is to check whether the date of extraction of the ore coincides with the period of World War II. The researchers use radiochronology, a technique that analyzes the material’s radioactive isotopes. Uranium is radioactive, which means that it decays at a fixed rate of time, turning into other chemical elements. What was once a cube of virtually pure uranium now has traces of thorium and protactinium. The team at PNNL, led by physicist Brittany Robertson, adapted radiochronology procedures to quantify these elements in the cube. Their concentration indicates how long ago the cube was produced.
The team is also refining this method to analyze cube impurities. This indicates where the uranium was mined – as different mines have different levels of impurity.
You can even find out in which laboratory the cube was produced. There were two main laboratories in Germany: Werner Heisenberg’s in Haigerloch (that’s what the Americans found) and Kurt Diebner’s in Gottow. Each used an outer layer of different chemicals to prevent the cube from oxidizing. Heisenberg used cyanide, while Diebner opted for styrene. To find out who made the cube, just find out the chemical composition of the layer. This analysis is being conducted by a second PNNL research group, led by physicist Carlos Fraga.
The team has not yet analyzed the lab cube, but it has already figured out where another cube came from, which is at the University of Maryland. It was found in Heisenberg’s laboratory by American troops – but, interestingly, its outer layer is styrene. After analyzing letters exchanged between physicists, the researchers found that Diebner sent some cubes to Heisenberg’s laboratory. The cube in Maryland, therefore, could be one of those.
The researchers intend to use these techniques to confirm the origin of known cubes. In addition to the Maryland and PNNL cubes, there is one at Harvard University and another at the Smithsonian Institution. To get an idea, this last one was discovered inside a drawer in New Jersey.
The technique can also be used in investigations of illegal trafficking in nuclear material – including Heisenberg cubes. Some may even be transiting the underground market – while others may simply be being used as a paperweight.