You know how in Captain America: The First Avenger there’s a Nazi-analogous organization trying to harness the power of a mysterious glowing cube in order to create a weapon of mass destruction that will overpower their enemies, only for their efforts to be sabotaged by the Allied forces and their cube to end up in a clandestine US research facility after the defeat of the Axis?

Did you know it happened for real?

Of course, it wasn’t an infinity stone that was powering the Nazis’ research – it was uranium. Neither did the cubes, of which there were over 1,000, end up in a secure SHIELD facility waiting for various Avengers to Assemble. In fact, they ended up … well, nobody’s really sure, actually – but thanks to some exciting new nuclear forensics research, a team at the Pacific Northwest National Laboratory (PNNL) is getting closer to an answer.

“[It’s] not only a really fun science project and scientific set of experiments but also somewhat of a history project,” explained PNNL researcher Brittany Robertson, presenting the results at the fall meeting of the American Chemical Society this week.

“We’re looking for different information and archived information and even … letters written between scientists, to try to figure out what we can measure and how we can actually make some interpretations.”

From the early 1940s, the Nazis and the US were locked in a race to figure out nuclear technology. The US had the Manhattan Project (and we all know how that turned out), and the Nazis had Werner Heisenberg – “like the Heisenberg, like the Heisenberg Uncertainty Principle,” Robertson laughs. “Heisenberg.” – and Kurt Diebner. At the heart of the research were these two-inch-long cubes of near-pure uranium: the hope was to exploit nuclear fission to transform them into plutonium, creating an atomic bomb.

Luckily, the program was disrupted before it could succeed, and the Allies confiscated many of the cubes after the war. But their fate after that is pretty murky: around 600 were shipped to the USA, but only about 12 are known today, with the rest being used in the US nuclear project, sold to private collectors and research institutions, or simply lost to the mists of time.

Even for the cubes we do know of, the provenance tends to be something of a mystery. The origins of the cube at PNNL are unknown, said lead researcher Jon Schwantes, with nobody sure how it even got to the laboratory at all. In fact, he explained, the team’s first job was to confirm that the cube was even part of the Nazi nuclear program at all.

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

Anecdotally, the cube at PNNL is a Heisenberg cube, but “[w]e didn't have any actual measurements to back up that claim,” Robertson explained. To prove the cube’s origin, she turned to radiochronometry, a technique that dates radioactive material by measuring how much it has decayed. For the Nazi cubes, that means measuring the relative levels of uranium, which they were originally made of, versus thorium and protactinium, which they would decay into over time.

Then there’s the cube’s coating, which the Nazis’ scientists used to protect the cubes from oxidation. Curiously for a supposed Heisenberg cube, the PNNL cube is coated in styrene – Diebner’s favored material.

“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.”

Other cubes have similarly mysterious origins: the team at PNNL were working in collaboration with the University of Maryland, which has a cube of their own – one that “found its way” to the department with a note saying “Taken from the reactor that Hitler tried to build. Gift of Ninninger.” But if the knowledge that there are a few hundred lost uranium cubes out there is worrying, remember: it’s better than the alternative.

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