Free Hitler's Terror Weapons by Geoffrey Brooks Page A

he knew the terrible danger it presented. In his initial report he had observed:
    â€œAn extraordinarily intensive neutron and gamma radiation goes hand in hand with energy producion. Even in achieving only 10kW power, 10 15 neutrons and gamma rays are created every second. The radiation is, therefore, 100,000 times greater than that produced in a large cyclotron. Even if a substantial amount of this radiation is absorbed in the core of the pile, nevertheless the working reactor would 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, 10 8 calories are used to produce heat leaving an excess of 5 to 10 19 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 admitted 43 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:
    â€œâ€¦ 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