Historians have long debated how close Nazi Germany came to achieving a self-sustaining nuclear reaction in its final reactor effort, known as the B8 pile. Werner Heisenberg, who led the work, said the team was close and needed only a little more uranium. But a new paper in PNAS Nexus argues that the project lacked enough uranium and heavy water to make the reactor design work.
The research grew out of physicist Timothy Koeth’s effort to trace the origins of a uranium cube he received in 2013. Koeth, a University of Maryland physicist and co-author of the paper, recognized it as one of the cubes used by German scientists in their attempt to build a reactor. Only 14 are known to exist today.
Koeth and then-graduate student Miriam “Mimi” Hiebert began tracking down the cubes, locating ten in the United States by 2019. Among them were examples held by the Smithsonian and Harvard, where one was reportedly shown to students in introductory physics classes.
The new study’s assessment indicates that the shortfall was not simply a matter of adding a small amount of uranium: the materials available were insufficient for the B8 design to reach criticality.
Sources: Ars Technica.