Werner Heisenberg and the German Uranium Project 1939 – 1945

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Myths and Facts

Klaus Gottstein
The results of a careful analysis of all the available information on the activities of Heisenberg and of his talks during the years 1939 to 1945 can be summarized in the following way. Like several other German physicists Heisenberg was drafted by German Army Ordnance when war began in Europe in September 1939 to investigate whether the energy from splitting Uranium nuclei by neutrons could be used for technical and military purposes. Heisenberg found that this is possible in principle but that military use would require such enormous industrial expenditures that it would take many years and would be impracticable while the war lasted. The project was therefore dropped by the Nazi government in 1942. Heisenberg even refrained from calculating a precise value for the critical mass of U 235. He was relieved that he was thus spared a moral decision between obeying an order to build the bomb or risking his life by refusing to be involved in the project or sabotaging it. He was happy to be confined to a project of building a small test reactor under civilian administration that the government had approved. In 1941 Heisenberg tried to get the opinion of Niels Bohr in Copenhagen on what the international community of nuclear physicist could possibly do or prevent regarding the long-range technical feasibility of making nuclear weapons. Bohr completely misunderstood the cautious approach of Heisenberg.

Written by physicsgg

September 13, 2016 at 9:18 am

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  1. Initially many scientists could and did hope that some principle would emerge which would prove that atomic bombs were inherently impossible. This hope faded gradually. Smyth Report 1946.

    If I have pure 235 each neutron will immediately beget two children and there must be a chain reaction which goes quickly .One neutron always makes two others in pure 235. In order to make 1024 neutrons I need 80 reactions one after the other. The mean free path is about 6 centimetres. In order to make 80 collisions, I must have a lump of radius of about 54 centimetres and that would be about a ton. Werner Heisenberg, Farm Hall transcripts 1945.

    Further, in the matter of an atomic bomb, it is not considered wise for the following reasons. For it to become a large magnitude explosion, a high temperature has to be attained. In order to do this, it is necessary for a time between 1/20 to 1/30 (micro) second, that it is confined by a substantial tamper. That is to say the tamper, the weight of this thing would be enormous and because of this the opinion is that it is not suitable (as a bomb). Yoshio Nishina, Tonizo transcripts 2nd July 1943.

    Martin Page

    March 29, 2017 at 10:19 am

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