Uranium from World War II reveals how close the Nazis were to an atomic bomb

The Nazis were far from completing a working reactor for their atomic bomb program, despite claims by the project's leader that it was almost ready, a new study finds.

The German physicist Werner Heisenberg wrote in 1947 that the reactor for the "Nazi bomb" project ‪— which culminated in Germany's B8 nuclear reactor ‪— was almost finished at the end of World War II.

Heisenberg, who led the reactor's development, claimed the reactor was "just insufficient" to create a self-sustaining fission reaction and that it lacked only a "relatively small amount of uranium" to work.

If it had worked, the B8 reactor would have confirmed that a fission chain reaction was possible, marking a key step toward the German development of an atomic bomb.

It could have also spurred the development of specialized fission reactors used to create weapons-grade plutonium from uranium.

Instead, the atomic bomb was developed first by the United States and was used to force the surrender of Japan in August 1945. (Germany had already surrendered in May 1945.) The new study, published Sept.

29 in the journal PNAS Nexus , used historical documents and forensic investigations of two of the project's surviving uranium cubes to refute Heisenberg's claim.

The new research indicates that the German B8 reactor had less than half the amount of "heavy water" and about half the amount of uranium it would have needed for a continuous chain reaction.

"My results argue that Heisenberg was off by roughly a factor of two," said first author Patrick Park , a doctoral student at Princeton University who co-wrote the study while at Columbia University.

Park said Heisenberg's mistake was understandable: His calculations were only approximate, and the project was relocated to a rock cellar in the town of Haigerloch, Germany, after Berlin was bombed.

My results argue that Heisenberg was off by roughly a factor of two.

Patrick Park, doctoral student at Princeton University "People were dying or starving and so these reactor calculations were not his first priority," while many details of neutron physics were unknown at that time, Park told Live Science in an email.

"Given these circumstances, I think he did the best he could." Heavy water To answer the question of how far the reactor for the Nazi bomb project got, the scientists began by tracing archival records of hundreds of uranium cubes that had been used by German scientists.

The B8 reactor consisted of five concentric circles of uranium cubes suspended on chains within the heavy water tank.