German Special Weapons
Unlike the United States' Manhattan Project, the WWII German Kernphysik (Nuclear Physics) program was never able to produce a critical nuclear reactor, despite many attempts by physicists Werner Heisenberg and Kurt Diebner. The German attempt to build a reactor was feeble and disorganized -- and their effort to build an atomic weapon nonexistent -- but the Allies didn't know that. At the end of the war, an Allied fact-finding mission captured the subcritical uranium piles and sent them to the United States.
Werner Heisenberg, a German theoretical physicist, proposed in 1925 in his famous Uncertainty Principle that we can know either the position or the momentum of a subatomic particle, but not both. Further, Heisenberg said, the more precisely we know the particle's momentum, the less we can know about its position. At the atomic scale, Newton's laws of classical mechanics give way to mathematical functions, developed by Erwin Schrödinger in 1926, that describe particle behavior in terms of probabilities. The work of Heisenberg and Schrödinger is the foundation of quantum mechanics, the theory that has proved eminently successful in describing and predicting the behavior of subatomic particles. Heisenberg is most famous for the Heisenberg uncertainty principle of quantum mechanics, but also spent much of his career investigating the complex dynamics of turbulence.
Edward Teller received his Ph.D. in physics in 1930 at the University of Leipzig in Germany, where he helped Werner Heisenberg lay the foundation of nuclear physics.
The nuclear arms race began with the race to develop the atomic bomb. Many dates and events could be chosen as the starting point. In 1932 James Chadwick demonstrated the existence of the neutron, or non-charged particle, within the nucleus of an atom. Later that year, J.D.Cockroft and E.T.S.Walton successfully split lithium atoms in a particle accelerator. In 1933, Leo Szilard first envisioned the dual potential of the atom when he surmised that the collision of neutrons within a chain reaction would release energy and speculated on the use of this energy in making bombs. Szilard formalized these thoughts in a patent application on July 4, 1934 that described
how explosions could be induced through chain reactions and introduced the concept of critical mass. It would be 2 years, however, before the British Admiralty accepted Szilard 's offer of his patents.
In contrast to prevailing studies that required a high energy source to accelerate positive-charged proton beams and alpha particles,Enrico Fermi experimentally bombarded 63 elements with neutrons, reasoning that little resistance would be encountered by uncharged particles entering the nucleus.One of the experimental elements was uranium. Over the next several years, the international scientific community focused on neutron bombardment as a more promising technology for splitting atoms and uranium as a key element. Enrico Fermi's team at the University of Rome originally thought that their bombardment of uranium by slow neutrons in the mid-1930s had produced elements heavier than uranium, or transuranic elements. By experiments which were carried out during the years 1936-38, Otto Hahn and Lise Meitner believed they could confirm Fermi's statement that the transuranium elements are formed by irradiating the heaviest elements with neutrons.
It is generally accepted that the atomic age began in Berlin with the discovery in 1938 that uranium can undergo nuclear fission. Earlier workers had achieved fission by bombarding uranium with neutrons, but did not recognize it as such.
When the discovery of nuclear fission was first reported in January 1939, it appeared that the chemists Otto Hahn and Fritz Strassmann had performed the crucial experiments, while the physicists Lise Meitner and Otto Frisch provided the first theoretical explanation of the fission process. Historical accounts have tended to emphasize that divide ever since, as did the award of the Nobel Prize in chemistry to Hahn alone. But history and the published record can be deceptive, and Nobel committees can make mistakes. Meitner was not present when the crucial experiments were made, having been forced to flee Berlin to exile in Sweden in the summer of 1938, when her native Austria was annexed by the Nazis. Meitner and nuclear physics were crucial to the discovery, but that Meitner's role was obscured by her forced emigration, the political conditions in Nazi Germany, and the deliberate "forgetting" of the postwar period.
Late in 1938, Lise Meitner, Otto Hahn and Fritz Strassman discovered the phenomenon of atomic fission. Meitner worked in Germany with physicists Otto Hahn and Fritz Strassmann until fleeing to Sweden to escape Nazi persecution. From her work in Germany, Meitner knew the nucleus of uranium-235 splits (fission) into two lighter nuclei when bombarded by a neutron. Interestingly, the sum of the particles derived from fission are not equal in mass to the original nucleus. During a visit with her nephew, Meitner speculated that release of energy--energy a hundred million times greater than normally released in the chemical reaction between two atoms--accounted for the difference. Still somewhat nervous about their finding, Frisch approached the eminent Danish physicist, Niels Bohr, who grasped the concept immediately with much enthusiasm.
Hahn published the experimental results in Naturwissenschaften on December 21, 1938. Meitner was not credited in the report signed by Hahn and Strassmann. Frisch, however, confirmed her explanation in a separate physics experiment in England. Hahn feared the result would be rejected if it were known to be tainted by "Jewish science" -- female Jewish science at that -- that he might even lose his position, and that all of German science might thereby suffer.
On January 13, 1939, Otto Frisch substantiated these results and, together with Lise Meitner,
calculated the unprecedented amount of energy released. Frisch applied the term "fission," from biological cell division, to name this process. Bohr sailed for the U.S. shortly thereafter, and upon his arrival announced the discovery on January 26, 1939, at the Princeton Monday Evening Journal Club, a weekly gathering of Princeton physicists. Almost immediately, related work emerged nearly everywhere.
On August 31, Bohr and John A.Wheeler, working at Princeton University, published their theory that the isotope uranium-235,present in trace quantities within uranium-238, was more fissile than uranium-238 and should become the focus of uranium research. In this publication, they also postulated that a then unnamed,unobserved transuranic element (referred to simply as 94 239 or, more descriptively,as "high octane ") produced during fissioning of uranium-238 would be highly fissionable.
Enrico Fermi and exiled Hungarian physicist Leo Szilard, realized the first split or fission could cause a second, and so on in a series of chain reactions expanding in geometric progression. They agreed not to publish their findings, lest Germany use them to produce a super weapon. Instead, Szilard and émigré Eugene Wigner persuaded Albert Einstein to write President Franklin D. Roosevelt and request atomic research receive high priority.
Physicists everywhere soon realized that if chain reactions could be tamed, fission could lead to a promising new source of power. What was needed was a substance that could "moderate" the energy of neutrons emitted in radioactive decay, so that they could be captured by other fissionable nuclei. Heavy water was a prime candidate for the job.
After the discovery of fission, Heisenberg was recruited to work on a chain-reacting pile in September 1939 by Nazi physicist Kurt Diebner. While the Americans under Enrico Fermi chose graphite to slow down, or "moderate," the neutrons produced in the fission of uranium 235 so that they could cause further fissions in a chain reaction, Heisenberg chose heavy water.
Heisenberg calculated the critical mass for a bomb in a December 6, 1939 report for the German Army Weapons Department. His formula, with the nuclear parameter values assumed at that time, yielded a critical mass in the hundreds of tons of "nearly pure" uranium 235 (U235) required for an exploding reactor, Heisenberg's model for a bomb at that point. This was vastly beyond what Germany could hope to produce. With uranium out of the question, the Germans decided to go for plutonium, which meant building an atomic pile [a nuclear reactor] to convert natural uranium into plutonium.
In March 1940, Otto Frisch met up with Rudolf Peierls in the United Kingdom, and they argued that if uranium 235 (0.7% naturally occurring) could be extracted from naturally occurring uranium 238, the amount needed for an atomic bomb could be measured in kilograms, rather than the early estimates of tons. They also suggested that, if the fissile component of the weapon was made in two parts each less than the critical mass, the bomb could be set off simply by bringing the two parts rapidly together.
In 1941, one of the leading German scientists at the University of Heidelberg, Walther Böthe, a highly regarded German physicist, greatly underestimated the diffusion path length of slow neutrons in graphite, apparently because graphite of inadequate purity was used in the German studies. Consequently, the German scientists selected heavy water as the moderator, rather than graphite, which was used in the U.S. program. These results were based upon mistaken calculations and gave Fermi an advantage. Heavy water was also chosen because Heisenberg's early experiments with paraffin as a moderator failed to produce any chain reaction.
German interest in heavy water was a major factor in the race to build the A-bomb. When, in late 1939, the Germans began ordering heavy water in very large quantities, Norsk Hydro management suspected "some kind of deviltry." Frédéric Joliot knew perfectly well what kind of deviltry, and with the cooperation of Norsk Hydro, the French managed to spirit the company's entire stock of heavy water, some 185 kilograms, out of the country.
Heisenberg's first experiments with heavy water at the Kaiser-Wilhelm Institute in Berlin-Dahlem and in Leipzig, Germany, were encouraging enough for him to promote nuclear energy to the German government.
The very scanty contact with the German physicists during the occupation contributed - as already mentioned - to strenghten the impression that the German authorities attributed great military importance to atomic energy. Werner Heisenberg and his mentor Niels Bohr had a pivotal meeting in September 1941 in Copenhagen. Bohr, a Jew, was living in occupied Denmark but had contact with physicists on the Allied side. Heisenberg's covert trip at great risk to see Bohr and his wife, Margrethe, in Copenhagen results in disaster. Something in this meeting destroyed their longstanding friendship. According to Bohr, Heisenberg travelled to Copenhagen to brag about his German colleagues' progress in building the bomb. Bohrwas shocked at his former student's nationalistic zeal. At the time Bohr had no knowledge of what the Allies were doing. Werner Heisenberg and C.F. von Weizsäcker were in Copenhagen on other business, but in a private conversation with Heisenberg they brought up the question of the military applications of atomic energy. Heisenberg expressed his scepticism because of the great technical difficulties that had to be overcome, but Heisenberg thought that the new possibilities could decide the outcome of the war if the war dragged on.
Heisenberg warned the German government in the fall of 1941 that the Americans were pursuing a nuclear explosive (plutonium) that could be made in a chain-reacting pile. The warning resulted in receiving the highest priority for his work from Albert Speer, Hitler's minister of munitions.
Weizsäcker had stated how fortunate it would be for the position of science in Germany after the victory to help so significantly towards this end with atomic weapons. But there was no possibility of carrying out such a large undertaking in Germany before the end of the war.
The German scientists had produced nuclear fission in the laboratory. They had also been looking at nuclear fusion and U-235 separations and were approaching criticality in a nuclear pile in a cave at Haigerloch. Their nuclear program was inhibited somewhat by a lack of enthusiasm on the part of Adolph Hitler, who believed the time frame was too long, and even more so by a serious miscalculation in its early stages.
After the War, Heisenberg recounted "It was a new situation for us scientists in Germany. Now for the first time we could get money from our government to do something interesting and we intended to use this situation. The official slogan of the government was: We must make use of physics for warfare.... We felt already in the beginning that if it were possible at all to actually make explosives it would take such a long time and require such an enormous effort that there was a very good chance the War would be over before that could be accomplished.... We definitely did not want to get into this bomb business. I wouldn't like to idealize this; we did this also for our personal safety. We thought that the probability that this would lead to atomic bombs during the War was nearly zero. If we had done otherwise, and if many thousand people had been put to work on it and then if nothing had been developed, this could have had extremely disagreeable consequences for us."
On 26 February 1942, Heisenberg spoke at a Berlin conference organized to garner support for the fission project. Heisenberg reported that a reactor could be used to power submarines, and to generate "...a new substance (element 94) ...which in all probability is an explosive with the same unimaginable effectiveness as pure uranium-235."
Until 1942 Heisenberg headed a small reactor research group in Leipzig and advised a second, larger group in Berlin. Heisenberg built an early experimental pile in Leipzig, alternating layers of uranium and paraffin, to test the properties of a chain reaction. The Leipzig pile burned in a fire caused by a pyrophoric reaction of its powdered uranium with air.
Allied bombing of Berlin forced Heisenberg to move his materials to Haigerloch in Wurttemberg, Germany. In 1944 it was rented by the Kaiser-Wilhelm-lnstitut für Physik (Kaiser Wilhelm Institute for Physics) in Berlin. The Atomkeller is a long, rectangular room, the walls are the rough, undisguised rock face. The whole tunnel reminds its original origin: an (uncompleted) railroad tunnel. The reactor prototype was once located at the end of this tunnel. The famous "B8"-experiment was carried out at the end of March and the beginning of April 1945. The reactor didn't become critical. Further calculations showed that a functioning nuclear reactor would have had to be about 1.5 times the size of this reactor. However, expanding the reactor was no longer possible in April 1945 due to the lack of both heavy water and additional quantities of uranium blocks.
The US Army Air Corps bombed the German nuclear production works near Berlin. Thus ended the German nuclear threat. Although General Groves was aware of this fact, he did not pass the information on to the scientists in the Manhattan Project.
In 1944, as Germany was falling, the Alsos Mission under Lieutenant Colonel Boris Pash and Samuel Goudsmit, its civilian scientist, gathered information on all aspects of Germany's advanced technology, particularly the development of atomic energy. The American intelligence force quickly nabbed all the German nuclear documentation and scientists they could find to keep them out of the hands of the Soviets. (Alsos was a thinly disguised code name; in Greek it means "grove.") The mission found that the Germans working on an atomic bomb under Werner Heisenberg were far behind the United States.
Hahn, who was involved with the desultory German effort to harness atomic power, was awarded the 1944 Nobel Prize (delayed in presentation until 1946) by an uninformed prize committee. Possibly anxious to defend the status of German science in the postwar years, he never bothered to correct the record.
A persistent historical debate still rages about the motivations of Hahn, Werner Heisenberg, and the other members of the German "Uranium Club." The 1993 book by the journalist Thomas Powers, "Heisenberg's War," argued that Heisenberg destroyed the German project from within. But Heisenberg, who was not a Nazi, compromised his principles by acquiescing in Nazi rule because he believed that it would return Germany to "its rightful place" as an economic and military leader in the world. Did he delay the German bomb project in order to prevent the Nazis from acquiring the bomb--as he claimed--or were they were not able to develop a bomb because they were unabile?
After the war Heisenberg maintained that he understood the principles of an atomic bomb, but that he had deliberately misled the German program into concentrating on reactors. In fact, under Heisenberg, everything was being done in Germany to develop atomic weapons.
After the war, Heisenberg and nine of his colleagues were interned at Farm Hall, a British country house. Hidden microphones recorded their reaction to the bombing of Hiroshima. Heisenberg did not understand bomb physics, and had vastly overestimated how much U-235 was needed. At Farm Hall Heisenberg had calculated that the amount of fissionable material necessary for a bomb was somewhere in the range of several metric tons.
The Germans were forced to forswear the production of atomic, biological, and chemical weapons as part of the Paris Treaties of 1955 (embodying the socalled Adenauer "nonnuclear pledge"), which cleared the way politically for West Germany to join the North Atlantic Treaty Organization (NATO).
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