Bengaluru: Scientists at the Pacific Northwest National Laboratory (PNNL) in Washington, USA, have developed new forensic tracking techniques that could locate lost uranium from the Nazi Germany atomic weapons program. Over 600 cubes of Uranium, that were parts of plans for a nuclear reactor and an atomic bomb, went missing from a secret underground laboratory at the end of World War 2 and were taken to the US. Until today, only a handful have been located while the others were likely trafficked.
The new technique was developed when researchers received access to three of the purported uranium cubes. Their findings were presented at a meeting of the American Chemical Society last week.
The tracking method
The technique used to test the cube’s origins is radiochronometry, or dating samples using natural radioactive isotopes (chemical elements with the same number of protons but different number of neutrons). Radiochronometry is regularly used by geologists to date ancient rocks and minerals, and the researchers hope that using the technique will reveal the age of the uranium. This in turn would potentially reveal where the original uranium was mined, giving more information about the origins of a cube.
The researchers also used other simpler techniques to track a cube’s journey and origins.
These cubes were called Heisenberg cubes after the German physicist Werner Heisenberg, one of the creators of the cubes. Heisenberg headed the Berlin group of German nuclear scientists, and as Allied forces made progress in 1944, moved his entire team and equipment to a secret underground cave below a castle in a small town in Germany.
Heisenberg’s group built a nuclear reactor here, composed of 664 uranium cubes that were submerged in a tank of heavy water and covered with graphite to protect from radiation exposure.
The experiment was not successful as the amount of uranium within these cubes was not enough to trigger a nuclear reaction. Heisenberg set out to increase the size of the cubes, working in collaboration with the two other groups of the German nuclear program — one at Leipzig and another at Gottow, the latter of which was headed by physicist Kurt Diebner.
In 1945, a mission associated with the Manhattan Project (the American mission to build an atomic weapon during WW2) tracked down the cave, leading Heisenberg to dismantle the reactor and bury the uranium, which was confiscated by the Americans. The cubes were never recorded to have entered the US, and went unaccounted.
German physicists during the Nazi regime are thought to have built over 1,200 cubes of uranium. Over 400 cubes from a different research site were smuggled into the Soviet Union’s black market and disappeared.
Some of the cubes that entered America have been identified and have been preserved as artefacts, including the one at PNNL. The PNNL cube has been identified as a Heisenberg cube, but the researchers note that it has a styrene-coating which was originally found in cubes from Diebner’s lab. The researchers think that the cube was one of the few that Diebner sent to Heisenberg when he was trying to increase his uranium cube sizes.
Because each of the labs used different chemical coatings on their cubes to reduce oxidation, the team thinks the technique of analysing the coating for the source lab could also help potentially track down illegal uranium.
(Edited by Manasa Mohan)