Manhattan Project
In 1932, James Chadwick discovered the neutron. This particle could penetrate an atomic nucleus without being electrically repelled. Leo Szilard conceived the possibility of using neutrons to release energy in a nuclear chain reaction. He patented the process on the assumption that one could be produced in beryllium. This was not possible, but the discovery of nuclear fission by Otto Hahn and Fritz Strassmann in 1938 made an atomic bomb theoretically possible. There were fears that a German atomic bomb project would develop one first. In August 1939, Szilard and Eugene Wigner drafted the Einstein, Szilard letter. It warned of the potential development of extremely powerful bombs of a new type. They had it signed by Albert Einstein and delivered to President Franklin D. Roosevelt. The letter urged the United States to acquire stockpiles of uranium ore and accelerate research into nuclear chain reactions. Roosevelt called on Lyman Briggs of the National Bureau of Standards to head an Advisory Committee on Uranium. The committee reported back to Roosevelt in November that uranium would provide a possible source of bombs with destructiveness vastly greater than anything now known. In February 1940, the U.S. Navy awarded Columbia University $6,000 for graphite. A team including Enrico Fermi created the first nuclear fission reaction in the Americas. They verified the work of Hahn and Strassmann. The same team subsequently built prototype nuclear reactors in Pupin Hall at Columbia. They were not yet able to achieve a chain reaction.
The Chief of Engineers selected Colonel James C. Marshall to head the Army's part of the project in June 1942. Marshall created a liaison office in Washington, D.C., but established his temporary headquarters at 270 Broadway in New York. He could draw on administrative support from the Corps of Engineers' North Atlantic Division. It was close to the Manhattan office of Stone & Webster, the principal project contractor. He had permission to draw on his former command, the Syracuse District, for staff. Lieutenant Colonel Kenneth Nichols became his deputy. Because most of his task involved construction, Marshall worked in cooperation with Major General Thomas M. Robins. Groves felt that the name Development of Substitute Materials would draw attention. Since engineer districts normally carried the name of the city where they were located, Marshall and Groves agreed to name the Army's component the Manhattan District. Reybold officially created this district on the 13th of August. Unlike other districts, it had no geographic boundaries. Vannevar Bush became dissatisfied with Colonel Marshall's failure to get the project moving forward expeditively. He spoke to Harvey Bundy and Generals Marshall, Somervell, and Styer about his concerns. They advocated that the project be placed under a senior policy committee. Somervell and Styer selected Leslie Groves for the post. General Marshall ordered that he be promoted to brigadier general. Groves assumed command of the Manhattan Project on the 23rd of September 1942. Later that day, he attended a meeting which established a Military Policy Committee. The committee consisted of Bush, Styer, and Rear Admiral William R. Purnell. Tolman and Conant were later appointed as Groves' scientific advisers.
On the 29th of September 1942, United States Under Secretary of War Robert P. Patterson authorized the Corps of Engineers to acquire land by eminent domain at a cost of $3.5 million. About 1,000 families were affected by the order. Protests, legal appeals, and a 1943 Congressional inquiry were to no avail. By mid-November U.S. Marshals were posting notices to vacate on farmhouse doors. Some families were given two weeks' notice to vacate farms that had been their homes for generations. The ultimate cost of the land acquisition was only about $2.6 million. Initially known as the Kingston Demolition Range, the site was officially renamed the Clinton Engineer Works in early 1943. While Stone & Webster concentrated on production facilities, Skidmore, Owings & Merrill developed a residential community for 13,000. The population of Oak Ridge soon expanded well beyond initial plans. It peaked at 75,000 in May 1945. By that time, 82,000 people were employed at the Clinton Engineer Works. On the 16th of November 1942, Oppenheimer, Groves, Dudley and others toured the vicinity of the Los Alamos Ranch School. Oppenheimer expressed a strong preference for the site, citing its natural beauty. Patterson approved the acquisition of the site on the 25th of November 1942. Wartime land purchases eventually came to , but only $414,971 was spent. Work commenced in December 1942. During the war, Los Alamos was referred to as Site Y or the Hill. In December 1942, Groves dispatched Colonel Franklin Matthias and DuPont engineers to scout potential sites for plutonium production. Matthias reported that Hanford Site near Richland, Washington, was ideal in virtually all respects. It was isolated and near the Columbia River. Under Secretary Patterson gave his approval on the 9th of February, allocating $5 million for the acquisition of land. The federal government relocated some 1,500 residents of nearby settlements.
Natural uranium consists of 99.3% uranium-238 and 0.7% uranium-235. Only the latter is fissile, so it must be physically separated from the more plentiful isotope. Various methods were considered for uranium enrichment. Most of this work was carried out at Oak Ridge. Centrifuges failed, but electromagnetic separation, gaseous diffusion, and thermal diffusion technologies were successful. Electromagnetic isotope separation was developed at the University of California Radiation Laboratory. This method employed devices known as calutrons. The name derived from California, university, and cyclotron. Marshall and Nichols discovered that the process would require copper, which was in desperately short supply. Silver could be substituted in an 11:10 copper to silver ratio. On the 3rd of August 1942, Nichols met with Under Secretary of the Treasury Daniel W. Bell. He asked for the transfer of 6,000 tons of silver bullion from the West Point Bullion Depository. Ultimately, tons were used. Responsibility for the design and construction of the Y-12 plant was assigned to Stone & Webster in June 1942. The calutrons initially enriched the uranium-235 content to between 13% and 15%. They shipped the first few hundred grams to Los Alamos in March 1944. Only 1 part in 5,825 of the uranium feed emerged as product. Strenuous recovery efforts helped raise production to 10% by January 1945. Gaseous diffusion faced formidable technical difficulties. The highly corrosive gas uranium hexafluoride had to be used. A six-stage pilot plant was built at Columbia to test the process. In November 1942, the Military Policy Committee approved the construction of a 600-stage gaseous diffusion plant. M. W. Kellogg accepted an offer to construct the plant, which was codenamed K-25. Work on the main building began in October 1943. The production plant commenced operation in February 1945. By August, the last of the 2,892 stages commenced operation.
The second line of development pursued by the Manhattan Project used plutonium. Natural uranium is bombarded by neutrons and transmuted into uranium-239. This rapidly decays into neptunium-239 and then into plutonium-239. As only a small amount will be transformed, the plutonium must be chemically separated from remaining uranium. In March 1943, DuPont began construction of a plutonium plant on a site at Oak Ridge. It included the air-cooled X-10 Graphite Reactor. The reactor went critical on the 4th of November 1943 with about of uranium. A week later the load was increased to , raising its power generation to 500 kW. By the end of the month, the first 500 mg of plutonium was created. Gradual modifications raised the power to 4,000 kW in July 1944. X-10 operated as a production plant until January 1945. Work began on Reactor B, the first of six planned 250 MW reactors, on the 10th of October 1943. Watched by Compton, Matthias, DuPont's Crawford Greenewalt, Leona Woods and Fermi, the reactor was powered up beginning on the 13th of September 1944. Over the next few days, 838 tubes were loaded and the reactor went critical. Shortly after midnight on the 27th of September, operators began to withdraw control rods. Around 03:00 the power level started to drop. By 06:30 the reactor had shut down completely. Fermi contacted Chien-Shiung Wu, who identified the cause as neutron poisoning from xenon-135. Fermi, Woods, Donald J. Hughes and John Archibald Wheeler calculated the nuclear cross section of xenon-135. It turned out to be 30,000 times that of uranium. On the 5th of February 1945, Matthias hand-delivered the first shipment of 80 g of 95%-pure plutonium nitrate to a Los Alamos courier in Los Angeles.
The British and Americans exchanged nuclear information but did not initially combine their efforts. In 1940, 41, the British project Tube Alloys was larger and more advanced. British leadership initially opposed an offer by Bush and Conant in August 1941 to pool the nations' atomic efforts. The British did not have resources to carry it into development while devoting a large portion of their economy to the war. Tube Alloys soon fell behind its American counterpart. In January 1943, Conant notified the British that they would no longer receive atomic information except in certain areas. By March 1943, Conant decided that James Chadwick and one or two other British scientists were important enough for the bomb design team at Los Alamos. In August 1943, Churchill and Roosevelt negotiated the Quebec Agreement. This established the Combined Policy Committee to coordinate US and UK efforts. Canada was not a signatory, but the Agreement provided for a Canadian representative. An agreement known as the Hyde Park Aide-Mémoire, signed in late September 1944, extended the Quebec Agreement to the postwar period. It suggested that when a bomb is finally available, it might perhaps be used against the Japanese. The British Mission arrived in the United States in December 1943. It included Niels Bohr, Otto Frisch, Klaus Fuchs, Rudolf Peierls, and Ernest Titterton. More scientists arrived in early 1944. While those assigned to gaseous diffusion left by fall 1944, thirty-five working under Oliphant with Lawrence at Berkeley stayed until the end of the war. The nineteen sent to Los Alamos joined existing groups related to implosion and bomb assembly. Groves later said that the British scientists' direct contributions were helpful but not vital. He also stated there probably would have been no atomic bomb to drop on Hiroshima without Britain's impetus. Despite the Manhattan Project's own emphasis on security, Soviet atomic spies penetrated the program.
In 1943, development efforts were directed to a gun-type fission weapon with plutonium called Thin Man. Initial research on properties of plutonium was done using cyclotron-generated plutonium-239. Los Alamos received the first sample from the Clinton X-10 reactor in April 1944. Within days Emilio Segrè discovered a problem. Reactor-bred plutonium had a higher concentration of plutonium-240. This resulted in up to five times the spontaneous fission rate of cyclotron plutonium. It rendered it unsuitable for use in a gun-type weapon. A higher-velocity gun was suggested but found impractical. Work on an alternative method known as implosion had begun earlier under Seth Neddermeyer. Implosion used explosives to crush a subcritical sphere of fissile material into a smaller and denser form. The critical mass is assembled in much less time than with the gun method. The Fat Man design was initially a low priority fallback option. It was complex and required explosive lenses. In 1944, it was confirmed that plutonium from Hanford was not suitable for a gun-type bomb because of high proportion of plutonium-240. The first nuclear device ever detonated was an implosion-type bomb during the Trinity test. It was conducted at White Sands Proving Ground in New Mexico on the 16th of July 1945. The project was responsible for developing specific means of delivering weapons onto military targets. They used Little Boy and Fat Man bombs in atomic bombings of Hiroshima and Nagasaki in August 1945.
In the immediate postwar years, the Manhattan Project conducted weapons testing at Bikini Atoll as part of Operation Crossroads. It developed new weapons and promoted development of the network of national laboratories. The project supported medical research into radiology and laid foundations for the nuclear navy. It maintained control over American atomic weapons research and production until formation of United States Atomic Energy Commission in January 1947. Between 1944 and his resignation from the Trust in 1947, Groves deposited a total of $37.5 million. The Combined Development Trust purchased uranium oxide ore from companies operating mines in Belgian Congo. To avoid dependence on British and Canadians for ore, Groves arranged purchase of US Vanadium Corporation's stockpile in Uravan, Colorado. The raw ore was dissolved in nitric acid to produce uranyl nitrate. This was processed into uranium trioxide and reduced to highly pure uranium dioxide. By July 1942, Mallinckrodt was producing a ton of highly pure oxide a day. Turning this into uranium metal initially proved more difficult. Production was too slow and quality unacceptably low. A branch of Metallurgical Laboratory established at Iowa State College under Frank Spedding investigated alternatives. This became known as Ames Project. Its process became available in 1943.
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Common questions
When did the Manhattan Project officially begin under Leslie Groves?
Leslie Groves assumed command of the Manhattan Project on the 23rd of September 1942. He attended a meeting that same day which established a Military Policy Committee consisting of Vannevar Bush, Thomas Somervell, and Rear Admiral William R. Purnell.
Where was the Manhattan Project located in Oak Ridge Tennessee?
The site initially known as the Kingston Demolition Range was officially renamed the Clinton Engineer Works in early 1943. The population of Oak Ridge peaked at 75,000 in May 1945 with 82,000 people employed at the facility.
How much silver did the Manhattan Project use for calutrons?
Lieutenant Colonel Kenneth Nichols requested the transfer of 6,000 tons of silver bullion from the West Point Bullion Depository on the 3rd of August 1942 to substitute for copper in electromagnetic separation devices. Ultimately tons were used to construct the Y-12 plant at Oak Ridge.
What date did the first nuclear device detonated by the Manhattan Project occur?
The first nuclear device ever detonated was an implosion-type bomb during the Trinity test conducted at White Sands Proving Ground in New Mexico on the 16th of July 1945. This event marked the culmination of development efforts directed toward a gun-type fission weapon and alternative methods like implosion.
When did the United States Atomic Energy Commission replace the Manhattan Project?
The Manhattan Project maintained control over American atomic weapons research and production until the formation of the United States Atomic Energy Commission in January 1947. Between 1944 and his resignation from the Trust in 1947 Leslie Groves deposited a total of $37.5 million into the Combined Development Trust.