An Atomic History 0-3 8/11/02 7:31 AM Page 18 Chapter Two 19 THE FERMI-SZILARD PILE AND URANIUM RESEARCH The first government funding for nuclear research was allocated to purchase graphite and uranium oxide for the chain reaction experiments being organized by Fermi and World War II and the Manhattan Project Szilard at Columbia University in February 1940.2 This work, which began in New York 2 City, soon spread to Princeton, the University of Chicago, and research institutions in California.3 Even at this stage, the scientists knew that a chain reaction would need three major components in the right combination: fuel, moderator, and coolant. The fuel would contain the fissile material needed to support the fission process. The neutrons generated by the fission process had to be slowed by the moderator so that they could initiate addi- tional fission reactions. The heat that resulted from this process had to be removed by the coolant. Fermi’s initial research explored the possibility of a chain reaction with natural urani- The 1930s were a time of rapid progress in the development of nuclear physics. um. It was quickly determined that high-purity graphite served as the best neutron moder- Research accelerated in the early years of the Second World War, when new developments ator out of the materials then available.4 After extensive tests throughout 1940 and early were conceived and implemented in the midst of increasing wartime urgency. American 1941, Fermi and Szilard set up the first blocks of graphite at Columbia University in government interest in these developments was limited at first, but increased as the war September 1941. The graphite blocks were called a "pile," a name that was soon extended broadened, and as the possibility of a fission bomb became more probable. After Pearl to all other forms of reactors. Fermi and Szilard’s pile consisted of graphite blocks around Harbor and the final decision to pursue the bomb, the American effort was coordinated and a core of natural uranium. Unfortunately, the pile did not work well, largely because the partially militarized under the aegis of the U.S. Army Corps of Engineers. This led to the graphite blocks were not arranged for optimum results.5 Additional work perfected what establishment of the "Manhattan Engineer District," commonly known as the Manhattan came to be called the "lattice" arrangement, where channels of uranium coursed through a Project. matrix of graphite blocks.6 Another achievement of those early days was a better under- Before Pearl Harbor and direct American involvement in the war, the U.S. govern- standing of the chain reaction itself. In order for a chain reaction to be maintained, each ment’s role in nuclear research was basically that of an observer. Funding began only as fissioned nucleus had to send off at least one neutron that caused another nucleus to fis- Chicago Pile No. 1 was set up in the the promise of success increased in 1940 and 1941. The government certainly provided sion, and so on. A chain reaction that continued indefinitely at a constant rate had a multi- squash court underneath the west little direction during that time; it was the physicists themselves, especially the foreign sci- plication factor ("k") of 1, and was identified as "k = 1." When k was greater than 1, there stands of Stagg Field at the University entists, who organized a restriction on the publication of fission research in late 1939 and of Chicago. Courtesy of Argonne was an increase in both the fission rate and the reactor power level. If k was less than 1, 1 National Laboratory Archives, man- early 1940. Only the scientists knew what was at stake. the reaction could not sustain itself.7 aged and operated by The University The government’s involvement increased by degrees in response to Hitler’s military Even though Fermi and Szilard’s early work in chain reactions failed to achieve k = 1, of Chicago for the U.S. Department of Energy under Contract No. W-31-109- achievements. The first U.S. government agency to oversee nuclear developments, the they learned much from the experience. The usefulness of graphite as a neutron modera- ENG-38, negative 1-785. Advisory Committee on Uranium, was created in October 1939 in response to Einstein’s tor was firmly established. The lattice was found to be the best arrangement for the urani- letter to Roosevelt in August of 1939—and Hitler’s invasion of um and the graphite blocks to achieve maximum neutron efficiency.8 Most importantly, it Poland in September. The National Defense Research Council was learned, or at least affirmed, that piles stocked with natural uranium could produce (NDRC) replaced the Advisory Committee in June 1940, after nuclear energy in the form of heat, but would not produce a workable bomb. Fermi and the fall of France. The NDRC in turn was folded into the Office Szilard’s early work with piles demonstrated that a much higher concentration of uranium- of Scientific Research and Development (OSRD) after the inva- 235 would be needed for that task.9 sion of the Soviet Union in June 1941. In each of these steps, there was a growing coordination between the physicists and their government. More will be said about the agencies that pre- THE SEARCH FOR URANIUM-235 ceded the Manhattan Project, but it would be better to first exam- ine the developments that increased government interest in the Alfred Nier, at the University of Minnesota, first separated uranium-235 from natural two years before Pearl Harbor. Beginning with research into fis- uranium the same month Fermi and Szilard received government support for their chain sion chain reactions and the separation of uranium-235 from nat- reaction work. In March, Nier conclusively demonstrated that uranium-235 was the urani- ural uranium, these developments culminated in the discovery of um isotope responsible for fission.10 Almost immediately, this discovery threw a major the remarkable fissile properties of Element 94, soon to be roadblock in the path of the development of the atomic bomb. As Fermi’s chain reaction known as plutonium. research increasingly demonstrated, a uranium atomic bomb would be possible only with An Atomic History 0-3 8/11/02 7:31 AM Page 18 Chapter Two 19 THE FERMI-SZILARD PILE AND URANIUM RESEARCH The first government funding for nuclear research was allocated to purchase graphite and uranium oxide for the chain reaction experiments being organized by Fermi and World War II and the Manhattan Project Szilard at Columbia University in February 1940.2 This work, which began in New York 2 City, soon spread to Princeton, the University of Chicago, and research institutions in California.3 Even at this stage, the scientists knew that a chain reaction would need three major components in the right combination: fuel, moderator, and coolant. The fuel would contain the fissile material needed to support the fission process. The neutrons generated by the fission process had to be slowed by the moderator so that they could initiate addi- tional fission reactions. The heat that resulted from this process had to be removed by the coolant. Fermi’s initial research explored the possibility of a chain reaction with natural urani- The 1930s were a time of rapid progress in the development of nuclear physics. um. It was quickly determined that high-purity graphite served as the best neutron moder- Research accelerated in the early years of the Second World War, when new developments ator out of the materials then available.4 After extensive tests throughout 1940 and early were conceived and implemented in the midst of increasing wartime urgency. American 1941, Fermi and Szilard set up the first blocks of graphite at Columbia University in government interest in these developments was limited at first, but increased as the war September 1941. The graphite blocks were called a "pile," a name that was soon extended broadened, and as the possibility of a fission bomb became more probable. After Pearl to all other forms of reactors. Fermi and Szilard’s pile consisted of graphite blocks around Harbor and the final decision to pursue the bomb, the American effort was coordinated and a core of natural uranium. Unfortunately, the pile did not work well, largely because the partially militarized under the aegis of the U.S. Army Corps of Engineers. This led to the graphite blocks were not arranged for optimum results.5 Additional work perfected what establishment of the "Manhattan Engineer District," commonly known as the Manhattan came to be called the "lattice" arrangement, where channels of uranium coursed through a Project. matrix of graphite blocks.6 Another achievement of those early days was a better under- Before Pearl Harbor and direct American involvement in the war, the U.S. govern- standing of the chain reaction itself. In order for a chain reaction to be maintained, each ment’s role in nuclear research was basically that of an observer. Funding began only as fissioned nucleus had to send off at least one neutron that caused another nucleus to fis- Chicago Pile No. 1 was set up in the the promise of success increased in 1940 and 1941. The government certainly provided sion, and so on. A chain reaction that continued indefinitely at a constant rate had a multi- squash court underneath the west little direction during that time; it was the physicists themselves, especially the foreign sci- plication factor ("k") of 1, and was identified as "k = 1." When k was greater than 1, there stands of Stagg Field at the University entists, who organized a restriction on the publication of fission research in late 1939 and of Chicago.