Chasing Bitterfeld Calcium

During my searches for information on certain chemical reactions, techniques etc I occasionally come across some bizarre information. It happened most recently when I stumbled on the story of the CIA's, assisted by MI6, quest for information regarding Soviet progress towards the making of the atom bomb, in those heady days following the descent of the Iron Curtain over Europe. The US's Manhattan project was by then rolling plutonium-based nuclear weapons off the assembly line like they were hot cross-buns. By the end of WW II, the American nuclear bomb making effort employed an estimated 400,000 people, more than the automotive sector at the time. In contrast, the Soviet program was still in its embryonic phase.

The broad principles on how to produce a Pu²³⁹-based fission weapon were of course quite well understood by most nuclear scientists of that era but it had taken the US and its team of internationally renowned scientists five long years of full steam ahead research and development to turn these principles into deliverable weapons. The question now was how long it would take the USSR to bridge that valuable gap.

As early as 1946 allied intelligence services started to note shipments of high quality calcium metal from a major chemical complex in Bitterfeld, East Germany (back then firmly behind the Iron Curtain), to various destinations in the Soviet Union.

For the production of weapons grade Plutonium-239, Uranium is needed, lots of it and of high purity ('atomic grade uranium') too and atomic grade metallic Uranium is produced industrially by reducing its oxide (UO₂) or fluoride (UF₄ - so called Green Salt) with very pure calcium (or magnesium).

The shipments of high purity calcium were thus a clear indication that the Soviets were getting serious and monitoring the amounts allowed the allied intelligence agencies to estimate the quantities of metallic Uranium the Soviet bomb program was producing over time. From this metric it was possible to make a crude estimate of the ETA of the Soviet fission bomb.

The narrative of the monitoring of Soviet progress by means of calcium shipments reads like a real life spy story, including defectors, German scientists deported to Russia, clandestine monitoring, infiltration, export embargos on sensitive materials and components and even a last ditch attempt at nuclear sabotage involving Boron-10, ultimately abandoned when the Soviets successfully exploded their first fission bomb in August 1949.

Well worth the read if you're interested in a bit of Cold War, nuclear and chemical archaeology...

Chasing Bitterfeld Calcium