The task of formulating scientific research and national defense policies in wartime in the United States mainly falls on the shoulders of university presidents. On the one hand, this is because no one in the government office in Washington really understands and can guide American scientific research; On the other hand, the military scientific research department lacks outstanding talents.
President Roosevelt saw this weakness. He once spoke at a gathering of scientists, hoping that scientists would become an important force in safeguarding American security. Some university presidents on the east coast of the United States also believe that the National Academy of Sciences should do something for this war. They recommended President Bush of Carnegie University in Washington to discuss national defense research with President Roosevelt.
George H.W. Bush was an electronics expert and proficient in applied mathematics, and served as vice president of MIT. Bush held talks with President Roosevelt in early June. On June 27, Roosevelt ordered the establishment of the National Defense Research Committee, and Bush served as the chairman of this Committee. Its main task is to establish contact between the American Academy of Sciences and the American government, so that American scientific research can serve the American national defense independently and more effectively with the support of the American government. Briggs' uranium advisory committee has evolved into one of its subordinate committees. Bush reorganized the Committee, replaced two military members with five scientists, and strengthened the US nuclear research program. Only the nuclear research of Columbia University received $40,000 in additional support in June 1940 1. 1, and the material supply improved significantly.
After the establishment of the National Defense Research Council, it actually only controlled researchers related to the National Academy of Sciences. At that time, the Army had two other parallel institutions: the Military Service Laboratory and the National Aviation Advisory Committee. In order to unify all scientific research capabilities and serve the war more effectively, on the proposal of Bush, President Roosevelt ordered the establishment of the government scientific research and development office on June 28th, 194 1. Bush was appointed as the director of this office and became the highest coordinator of American wartime military scientific research. The former National Defense Research Council became a subsidiary of the Office of Scientific Research and Development. Conant, president of Harvard University, chemist and Bush's main assistant in nuclear research, took over as chairman of the National Defense Research Council. The Uranium Committee in Briggs was upgraded to a branch of the Office of Scientific Research and Development, also known as S- 1 Committee. In this way, nuclear research has become one of the most important military research projects in the United States during wartime.
While szilard, Fermi and others actively strive for the support of the US government and engage in nuclear research with military application as the ultimate goal, another purely academic research laboratory has inadvertently approached the door of atomic bomb research.
Lawrence, inventor of cyclotron and winner of the Nobel Prize in Physics, is very enthusiastic about the improvement of accelerator technology and the construction of a larger accelerator in the Radiation Laboratory of the University of California, Berkeley. 1940, he got more than 100 dollars from Rockefeller Foundation and built a cyclotron weighing 4900 tons. Some of his physics friends, such as Macmillan and Abelson, used the high-energy particle beam generated by Lawrence cyclotron to do various nuclear experiments.
At the beginning of 1940, Macmillan and Abelson discovered the existence of the 94th element plutonium -239 predicted by Bohr in their experiments. Plutonium -239 is produced by absorbing a neutron from uranium -238 and decaying it twice. Its life span is 24,000 years, and its chemical properties are very different from those of uranium. Their findings were published in the June issue of Physical Review.
1941February, Berkeley chemist Seeburg officially confirmed the production of plutonium -239 by chemical method, and began to systematically determine its properties. According to Bohr's prediction, plutonium -239 is also a fissionable element. After reading the article, chadwick, one of the hosts of British nuclear research, immediately asked the United States to stop leaking more information through diplomatic channels. 1940 12.28 cockcroft, another important British nuclear physicist, sent a letter to Lawrence through Fowler, the British science and technology representative in the United States, reminding him of the potential military application value of plutonium. Because of radar research, Macmillan soon returned to MIT. With his advice and Lawrence's help, Fermi's colleague segre in Rome succeeded Macmillan. They confirmed the fissionability of plutonium -239 in March of 194 1.
194 1 at the beginning of the year, many American physicists put forward their own views on the work of Briggs uranium Committee. Bush asked Compton, an academician of the National Academy of Sciences and director of the physics department of the University of Chicago, to organize some people who are "qualified to judge nuclear research" to conduct a comprehensive textual research on the nuclear program. After discussion with members of Briggs Committee, Compton Committee submitted its first report on May 17. The report discusses the military uses of slow neutrons, including radioactive pollution caused by fission, reactors powered by submarines, and the assembly of atomic bombs with high-purity uranium -235 or other fissionable elements. Although the report puts forward the importance of nuclear power in the future, it is not optimistic about the successful time, especially the separation of isotopes, and fails to make positive suggestions on the role of atomic bombs in the war at that time.
Lawrence is a member of the radar group of the National Defense Research Council. Influenced by his friends in nuclear physics, especially British friends, he became more and more interested in the military application of nuclear research. Lawrence proposed to transform his 37-inch cyclotron into a mass spectrometer for separating uranium isotopes. 194 1 March, he formally asked bush to support Berkeley's nuclear research financially. 1 1 In July, he submitted a report to the Compton Committee, which specifically proposed the structure of the atomic bomb for the first time in the history of American nuclear research. "If there are a lot of 94 elements, fast neutrons can also produce a chain reaction, and the speed at which this reaction releases energy will be explosive, so it can be regarded as a' super bomb'."
Neither Briggs' Uranium Committee nor Compton's two reports made any positive suggestions on the atomic bomb. Contrary to the United States, Britain put forward positive and optimistic suggestions on the future of the atomic bomb. It confuses Bush, conant and some other American physicists and thinks it is necessary to re-examine the whole nuclear research. Bush reorganized the uranium commission again and added an important nuclear physicist. He asked conant to talk to Lawrence and Compton, hoping that Lawrence would do more for nuclear research, and once again asked Compton to organize physicists from the National Academy of Sciences to conduct a comprehensive inspection of nuclear research.
1941165438+16 October, Compton formally submitted the third report of his Committee, which wrote: "It is very important for the security of the country and the free world to go all out to develop the atomic bomb ... It must be seriously considered, and within a few years, it will be used as described in the report. The report estimates that the critical mass of the atomic bomb is 2 ~ 100 kg. Because the nuclear reaction cannot be completely carried out when the atomic bomb explodes, 1 kg uranium -235 can generate an explosive force equivalent to 300 tons of TNT explosive. If we go all out, the atomic bomb will take 3-4 years to succeed.
After receiving Compton's report, Bush immediately reported to President Roosevelt. Roosevelt's answer is that if the atomic bomb is feasible, we must build it first!
The central task of S- 1 Committee is to study whether the United States can build an atomic bomb before the end of the war. The nuclear research group of Carnegie University has proved that when fast neutrons cause nuclear fission in uranium, more than 80% of the fission comes from uranium -235. According to the latest experimental data, Oppenheimer of the University of California, Berkeley estimated that the critical mass of the atomic bomb was 2.5 ~ 5 kg.
Another key issue of the atomic bomb is whether enough fissile material can be obtained in a short time. Isotopes with different masses cannot be separated by chemical methods, and uranium isotopes have large mass and small mass difference, so it is very difficult to separate. At that time, American scientists were already studying four different uranium isotope separation methods:
(1) diffusion method. It uses Clausius heat balance principle to separate isotopes of different masses, and the US Naval Laboratory is very keen on this method. The disadvantage of this method is that it is too inefficient.
(2) centrifugation. It uses different centrifugal forces when gases with different masses rotate to separate isotopes. In principle, it can be efficient. Yuri of Columbia University and Pims of University of Virginia have done a lot of work in this field, mainly involving materials and centrifugal pumps.
(3) Gas diffusion method. It uses gases with different mass to separate isotopes through different permeability coefficients of some porous membranes. Deng Ning of Columbia University estimates that if the fluoride gas of natural uranium passes through 5000 layers of membranes, the content of uranium -235 in uranium fluoride can meet the requirements of atomic bomb materials.
(4) Electromagnetic separation method. It uses different deflections of charged particles with different masses in the magnetic field to separate uranium isotopes. In the summer of 194 1, Lawrence broke through this obstacle in experiments and opened the way for large-scale electromagnetic separation of uranium isotopes.
The production of plutonium 239, another fissile material, depends on the successful construction of self-sustaining chain reactor and the chemical separation of plutonium 239 from uranium. The neutron multiplication coefficient of Fermi experimental reactor buffered by graphite in Columbia University has reached above 0.9, and physicists believe that this coefficient can be improved with the improvement of material purity. Another kind of reactor with heavy water as buffer is also under study, and the supply of raw materials needed for nuclear power plants has not encountered great difficulties.
194 1 At the beginning of the year, about 2,000 tons of uranium oxide were stored in North America, and uranium mines in the United States and Canada can provide hundreds of tons of uranium products every month. S- 1 Committee estimates that the smallest atomic bomb only needs less than 10 kg of uranium -235, and the uranium oxide required for refining each kg of uranium -235 will be less than 1 ton. A reactor only needs a few hundred tons of uranium oxide. Therefore, the supply of uranium oxide is not a problem. At the same time, S- 1 Committee also plans to purchase a large amount of graphite and heavy water for the development of the reactor.
19411On February 6th, Bush called Compton and others to Washington, officially conveying President Roosevelt's order to "go all out to develop an atomic bomb". At the meeting of S- 1 Committee, conant announced that he would be Bush's personal representative in S- 1 Committee to coordinate the progress of the nuclear program. He agreed to study four uranium isotope separation methods at the same time to ensure the provision of nuclear materials for the development of atomic bombs. At the meeting, the person in charge of each specific project plan was determined: Murfrey, director of the research department of Standard Oil Company, was appointed to be responsible for all the project planning issues related to research; Yuri is responsible for the study of uranium isotope gas separation; Lawrence is responsible for the electromagnetic separation of uranium; Compton is responsible for the development of reactors, the separation and production of plutonium, and the theoretical research of fast neutrons and atomic bombs themselves.
As early as 1940, Compton began to organize his own nuclear research group in the Physics Department of the University of Chicago. Gradually make Chicago an information exchange center for American nuclear research. After receiving the instruction from S- 1 Committee, he immediately reorganized the nuclear research team in Chicago and upgraded it to a large-scale research plan code-named "Metal Project", giving it the right to mobilize the nuclear research power in the United States. Compton also established a laboratory specializing in nuclear research in the Department of Physics, codenamed "Metal Laboratory", and a large number of outstanding physicists were invited to work in the laboratory.
That's when America's nuclear research program was formed. As a result, the greatest weapon in human history-political marriage will be realized in the next few years, and the era of atomic diplomacy will quietly come to the world. Human beings, including presidents, presidents, prime ministers and kings, all have the shadow of "atom" in their minds, which makes everyone fidgety, especially during the long "Cold War" period.