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

reactor. The author was Professor Fritz Houtermans, a Jewish scientist who was perhaps the most brilliant physicist in the field of chain reaction theory in the Third Reich. He was employed at the Post Office Research Institute under Baron Manfred von Ardenne at the Lichterfelde-Ost laboratory in Berlin. The Post Office research was funded independently. The Postmaster-General, Dr Wilhelm Ohnesorge, was known as a pro-Bomb Cabinet Minister close to Hitler.

The primary purpose of the report was to show the quickest and most effective means of having a working nuclear pile. It was the obvious first stepping stone into the atomic age. Houtermans also explained how a new explosive U239 (plutonium) could be bred in his reactor. He argued that if heat and energy were not required, then the use of heavy water or graphite as a moderator was not necessary. If the reactor was required only for the production of radioisotopes, then a carbon-based substance in a very low temperature was all that was needed.

What he had observed in the course of his experiments with moderators was that hydrogen molecules in carbon compounds absorbed far fewer neutrons in extreme sub-zero temperatures. It was almost certainly attributable to the nuclear Doppler Effect: he thought it probable that the Doppler Effect alone would enable a liquid carbon substance to be used as moderator. He considered the most favourable to be liquid methane, CH4, a colourless, odourless, flammable gas which is liquid in the temperature range – 164°C to – 186°C.

In common with all other Reich physicists, Houtermans was unaware of the stabilizing influence of the delayed neutrons of fission, but he had no concerns regarding the safety and stability of his design. Since the machine only operated at a very low temperature, the chain reaction would automatically collapse once the temperature began to rise substantially towards freezing point. While in theory he planned to use regulating rods to control neutron multiplication, in practice Houtermans would have found his reactor unexpectedly stable due to the unsuspected effect of the delayed neutrons.

Summarizing the paper in a section headed The Significance of a Chain Reaction in a Low Temperature Environment as a Neutron Source and as an Apparatus for Transforming Isotopes, Houtermans confirmed that because U239 (i.e. Pu239 plutonium) is a different element from uranium and, therefore, chemically distinct, concentrations of Pu239 should be obtainable relatively easily by chemical separation from the spent reactor fuel, and this would be an explosive, since it was also fissionable.

Houtermans’ paper was the first properly argued scientific thesis to enter circulation in Hitler’s Germany proposing a simple, lowtemperature atomic pile for the production of large quantities of radioisotopes and the bomb material plutonium. It was perfectly clear to Heisenberg that Houtermans’ methane pile would run. Once Ohnesorge, the Postmaster-General, saw the report he would have brought it to the attention of Hitler.

Within a tamper of U238, plutonium has a critical mass of about 11 kilos, but substantially less is required depending on the force of the implosion designed to detonate the bomb. Where the compression factor is three, for example, then only a few kilos of pure plutonium are needed. Five kilos of plutonium isotopes were produced during the fission cycle of a single reactor for every 20 tonnes of U238.

In a biography Heisenberg was quoted as saying that a faction comprising von Weizsäcker, Karl Wirtz, Peter Jensen and Houtermans met on several occasions to discuss the implications of the report, for:

“We were not absolutely sure, but we now saw that it was almost certain. Von Weizsäcker in particular and I were deeply disturbed. It now looked like it was definitely possible to make a reactor. We agreed that if we could make them, then the Americans could too. If they could make reactors, then plutonium was probably possible too, and so on. It was from September 1941 that we saw before us an open road leading to the atom bomb.”56

In another work, Heisenberg explained how he saw things at the time:

“The situation for physicists in the United States, especially for emigrés from Germany, was totally different from our own. In America they would be convinced that they are fighting for a just cause and against an evil one. The emigrés, precisely because they had been welcomed so hospitably by the Government of the United States, would have felt obliged to contribute to the best of their ability to the American cause. But is an atom bomb, which can kill 100,000 civilians at a stroke, a weapon like all the others? Can one justify the atom bomb with the dictum ‘A just end, but not an evil end, justifies the means’? Is it ethical therefore to build atom bombs for a just cause but not for an evil one? And if one accepts the principle, and it is a principle which has been imposed repeatedly throughout history, who decides what is a just cause and what an evil one? It is easy enough to establish that Hitler and National Socialism is evil. But is the American cause good? Is the principle not also valid that a society is to be condemned as evil by its choice of means? I replied, ‘Why don’t you speak with Niels Bohr in Copenhagen about this? If he is of the opinion that we are wrong to do this work on uranium and we should abandon it, I would find that a persuasive argument.’”57

The Meeting in Copenhagen with Bohr

Niels Bohr (1885–1962) had been appointed Professor of Physics at the University of Copenhagen in 1916 and was awarded the Nobel Prize in Physics in 1922. Heisenberg had been his pupil during the period 1924 to 1926. He was Jewish and emigrated from Denmark in 1943 in advance of the pogrom of Danish Jews. Bohr was understandably suspicious of Heisenberg, but, as the latter was unaware of this, it was arranged for the two of them to meet during a lecture at Bohr’s Copenhagen Institute in 1941. Heisenberg’s ostensible purpose seems to have been