Science TechnologyTuesday, 6 October 2026·The Hindu - Science
Heisenberg’s B8 reactor and Nazi nuclear programme: PNAS Nexus study revises how close Germany was to an atom bomb
A 2026 study in PNAS Nexus used uranium cubes and heavy-water data to show Werner Heisenberg’s B8 pile was far from criticality.
Key highlights
Direct fact
In 2026, a PNAS Nexus study on Werner Heisenberg’s B8 pile at Haigerloch, Germany, used uranium-cube measurements and heavy-water records to show that Nazi Germany’s reactor effort was not close to criticality.
Key specifics
- The B8 pile had 664 uranium cubes suspended on chains in about 1,400 litres of heavy water.
- Researchers measured one surviving cube at 18.535 g/cm3, below solid uranium’s 19.01 g/cm3, showing it was porous.
- Another cube contained 0.724% uranium-235 by mass, indicating natural uranium rather than enriched uranium.
- The study estimated B8’s neutron multiplication factor at 0.942, while a reactor must reach 1.0 to become critical.
- Simulations suggested B8 would have needed at least 2,994 kg of uranium and 3,411 litres of heavy water to become critical.
Exam lens
Science & technology MCQ focus: B8 pile, 664 uranium cubes, 0.942 multiplication factor, 1.0 criticality threshold, Haigerloch in Germany — a likely TNPSC one-liner on nuclear reactor basics and wartime science.