Hitler's Terror Weapons, Brooks, Geoffrey [cat reading book .txt] 📗

obviously require the provision of the most comprehensive biological shielding against radiation. This applies especially at the ‘switching-on’ of the machine, i.e. at criticality. At the moment when the temperature reaches the stationary value of 100°C, 108 calories are used to produce heat leaving an excess of 5 to 1019 neutrons and gamma rays liberated.”

The very low temperature uranium pile would produce nothing but radioisotopes and the intensely radioactive decay products of nuclear fission. Radioisotopes do have modern applications in medicine, biochemistry, biology and industry, but Professor Harteck saw another use for them.

After the war Harteck admitted43 that his idea in proposing to build a sub-zero uranium pile was to obtain nuclear waste for use against the populations of enemy cities. This seems to have been the first time that radiological material was being seriously suggested for military purposes. Such weapons are not outlawed by international treaties, since they are not classified as chemical. The evidence suggests that Hitler was prepared to entertain radiological warfare to stave off defeat but might not have resorted to it early on in the war unless he thought it would guarantee him victory.

Professor Harteck set about building an experimental sub-critical pile immediately. His idea was simple. Dry ice sublimates slowly at a temperature of – 78°C and is as pure as one part in a million. Its oxygen atoms do not absorb neutrons in significant quantities at very low temperatures. Concluding that carbon dioxide ice was an ideal moderator for his proposed experiment, Harteck asked permission of the Heereswaffenamt to proceed and went ahead with it at once.

He had useful contacts with the firm of I G Farben, and on 8 April 1940 he induced the firm’s research director, Dr Herold, to make him a gift of a 15-tonne block of dry ice to be delivered at the end of May. The War Office agreed to supply a railway wagon to expedite the consignment from Merseburg to Hamburg, and Harteck wrote to Diebner asking for 300 kilos of uranium. This figure was on the low side, but Harteck thought that it was all that was available.

It must have been obvious that Harteck was expecting to perform his experiment within a week of receiving his 15-tonne block of dry ice. Diebner had only 150 kilos of uranium oxide at Berlin-Dahlem, but Heisenberg was waiting for a large delivery from the War Ministry and probably had a large hoard besides. Diebner promised Heisenberg that the large amount would arrive in June and requested him to settle privately with Harteck.

Heisenberg suggested to Harteck in a letter that he was exaggerating the urgency of his experiment, since there were a number of preparations to be made first:

“… of course if there is for any reason any urgency in your experiments, you can go first by all means. But I should like to suggest that for the time being you content yourself with just 100 kilograms.”

Heisenberg concluded in a very reasonable vein that he was quite prepared to let Diebner make the final decision. Harteck replied by return, emphasizing the obvious urgency, and begged Heisenberg to loan him from 20 May, for three weeks at the most, as much of his Leipzig stock as he possibly could allow. In the expectation that Heisenberg would relent, Harteck asked Dr Herold to delay shipping the ice until the last possible moment and spoke to Diebner twice to emphasize his need for a minimum supply of 600 kilos of uranium oxide.

At the end of May Diebner loaned him 50 kilos and Dr Riehl of the Auer Company brought him 135 kilos more. Heisenberg sent nothing. When the block of ice arrived at the beginning of June the experiment was doomed and the only useful information it yielded was criteria for the distribution of neutron density in certain arrangements of uranium oxide and dry ice44.

Heisenberg’s non-cooperation prevented Harteck from obtaining a figure for neutron multiplication. This would have enabled Harteck to calculate the quantity of materials he needed for a working pile. Both Harteck44 and Wirtz45 made this point subsequently.

A Windfall of Uranium Oxide: Harteck Tries Again

There was no shortage of uranium oxide in German-occupied Europe. In May 1940 German forces arriving at Oolen in Belgium had discovered at the warehouses of the Union Minière Company over 1200 tons of uranium oxide and 1000 tons of other refined uranium metals. The British Government had known about this stock since early 1939 but had dropped a plan to purchase it outright and so remove it from proximity to Germany. The President of Union Minière, Edgar Sengier, appears to have made a purely business decision to leave the material for the Germans when they invaded so that his company would find favour with Hitler should he emerge victorious in the coming war in western Europe. Sengier then ordered the uranium mines at Katanga in the Belgian Congo flooded and had the mined ores shipped from Lobito to the United States. In October 1939 he transferred his offices to New York46.

The Germans controlled the Joachimstal mines in Czechoslovakia and thus held virtually all the uranium in Europe. There was in fact so much uranium in their hands that Professor Harteck set about planning his ambitious second experiment, a heterogeneous design consisting of 20 tonnes of uranium oxide in a lattice of shafts embedded throughout a 30-tonne block of dry ice. As soon as he announced his intention, he ran up against the determined opposition of Heisenberg, who argued that the experiment was so big that all Harteck would learn from it was a great deal about 20 tonnes of dirty uranium oxide and 30 tonnes of dry ice. Why Harteck thought that was something worth knowing he could not imagine. He expected that it would not work, however, or at least not unless Harteck sent the uranium oxide to a factory for purification first.

Harteck then came under growing pressure from other quarters, probably orchestrated by Heisenberg, and these argued that it was too extravagant