Manhattan Project
Manhattan District | |
---|---|
U.S. Army Corps of Engineers | |
Garrison/HQ | Oak Ridge, Tennessee, U.S. |
Anniversaries | 13 August 1942 |
Engagements | |
Commanders | |
Notable commanders | |
Insignia | |
Manhattan District shoulder sleeve insignia |
The Manhattan Project was a program of research and development undertaken during
The project resulted in two types of atomic bombs, developed concurrently during the war: a relatively simple
The project was also charged with gathering intelligence on the
The first nuclear device ever detonated was an implosion-type bomb during the
Origins
The
They had it signed by
In February 1940, the
Briggs proposed spending $167,000 on research into uranium, particularly the uranium-235 isotope, and plutonium, which was discovered in 1940 at the University of California.[8][a] On 28 June 1941, Roosevelt signed Executive Order 8807, which created the Office of Scientific Research and Development (OSRD),[10] with Vannevar Bush as its director. The office was empowered to engage in large engineering projects in addition to research.[8] The NDRC Committee on Uranium became the S-1 Section of the OSRD; the word "uranium" was dropped for security reasons.[11]
In Britain, Frisch and Rudolf Peierls at the University of Birmingham had made a breakthrough investigating the critical mass of uranium-235 in June 1939.[12] Their calculations indicated that it was within an order of magnitude of 10 kilograms (22 lb), which was small enough to be carried by a bomber of the day.[13] Their March 1940 Frisch–Peierls memorandum initiated the British atomic bomb project and its MAUD Committee,[14] which unanimously recommended pursuing the development of an atomic bomb.[13] In July 1940, Britain had offered to give the United States access to its research,[15] and the Tizard Mission's John Cockcroft briefed American scientists on British developments. He discovered that the American project was smaller than the British, and not as advanced.[16]
As part of the scientific exchange, the MAUD Committee's findings were conveyed to the United States. One of its members, the Australian physicist
On 9 October 1941, President Roosevelt approved the atomic program after he convened a meeting with Vannevar Bush and Vice President Henry A. Wallace. He created a Top Policy Group consisting of himself—although he never attended a meeting—Wallace, Bush, Conant, Secretary of War Henry L. Stimson, and the Chief of Staff of the Army, General George C. Marshall. Roosevelt chose the Army to run the project rather than the Navy, because the Army had more experience with management of large-scale construction. He agreed to coordinate the effort with that of the British and on 11 October sent a message to Prime Minister Winston Churchill, suggesting that they correspond on atomic matters.[19]
Feasibility
Proposals
The S-1 Committee meeting on 18 December 1941 was "pervaded by an atmosphere of enthusiasm and urgency"
Meanwhile, there were two lines of investigation into
Bush and Conant then took the recommendation to the Top Policy Group with a budget proposal for $54 million for construction by the United States Army Corps of Engineers, $31 million for research and development by OSRD and $5 million for contingencies in fiscal year 1943. They sent it on 17 June 1942, to the President, who approved it by writing "OK FDR" on the document.[22]
Bomb design concepts
Compton asked theoretical physicist
To review this work and the general theory of fission reactions, Oppenheimer and Fermi convened meetings at the University of Chicago in June and at the University of California in July 1942 with theoretical physicists
The properties of pure uranium-235 were relatively unknown, as were those of plutonium, which had only been discovered in February 1941 by
As the idea of the fission bomb was theoretically settled—at least until more experimental data was available—Edward Teller pushed for discussion of a more powerful bomb: the "super", now usually referred to as a "
Organization
Manhattan District
The
Because most of his task involved construction, Marshall worked in cooperation with the head of the Corps of Engineers Construction Division, Major General Thomas M. Robbins, and his deputy, Colonel Leslie Groves. Reybold, Somervell, and Styer decided to call the project "Development of Substitute Materials", but Groves felt that this 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 13 August. Informally, it was known as the Manhattan Engineer District, or MED. Unlike other districts, it had no geographic boundaries, and Marshall had the authority of a division engineer. Development of Substitute Materials remained as the official codename of the project as a whole but was supplanted over time by "Manhattan".[39][40]
Marshall later conceded that, "I had never heard of atomic fission but I did know that you could not build much of a plant, much less four of them for $90 million."
Marshall and Nichols began assembling the necessary resources. The first step was to obtain a high priority rating for the project. The top ratings were AA-1 through AA-4 in descending order, although there was a special AAA rating reserved for emergencies. Ratings AA-1 and AA-2 were for essential weapons and equipment, so Colonel Lucius D. Clay, the deputy chief of staff at Services and Supply for requirements and resources, felt that the highest rating he could assign was AA-3, although he was willing to provide a AAA rating on request for critical materials if the need arose.[46] Nichols and Marshall were disappointed; AA-3 was the same priority as Nichols' TNT plant in Pennsylvania.[47]
Military Policy Committee
Vannevar Bush became dissatisfied with Colonel Marshall's failure to get the project moving forward expeditiously
Somervell and Styer selected Groves for the post; General Marshall ordered that he be promoted to brigadier general,
On 19 September, Groves went to
One of Groves' early problems was to find a director for Project Y, the group that would design and build the bomb. The obvious choice was one of the three laboratory heads, Urey, Lawrence, or Compton, but they could not be spared. Compton recommended Oppenheimer, who was already intimately familiar with the bomb design concepts. However, Oppenheimer had little administrative experience, and, unlike Urey, Lawrence, and Compton, had not won a Nobel Prize, which many scientists felt that the head of such an important laboratory should have. There were also concerns about Oppenheimer's security status, as many of his associates were communists, including his wife, Kitty; his girlfriend, Jean Tatlock; and his brother, Frank. A long conversation in October 1942 convinced Groves and Nichols that Oppenheimer thoroughly understood the issues involved in setting up a laboratory in a remote area and should be appointed as its director. Groves personally waived the security requirements and issued Oppenheimer's clearance on 20 July 1943.[58][59]
Collaboration with the United Kingdom
The British and Americans exchanged nuclear information but did not initially combine their efforts; during 1940-41 the British project (
By March 1943 Conant decided that
When cooperation resumed after the Quebec Agreement, the Americans' progress and expenditures amazed the British. Chadwick pressed for British involvement in the Manhattan Project to the fullest extent and abandoned hopes of an independent British project during the war.
The Combined Policy Committee created the
Groves appreciated the early British atomic research and the British scientists' contributions to the Manhattan Project but stated that the United States would have succeeded without them, although not in time for the August 1945 bombing of Hiroshima.
Project sites
Oak Ridge
The day after he took over the project, Groves went to Tennessee with Colonel Marshall to inspect the proposed site there, and Groves was impressed.[78][79] On 29 September 1942, United States Under Secretary of War Robert P. Patterson authorized the Corps of Engineers to acquire 56,000 acres (23,000 ha) of land by eminent domain at a cost of $3.5 million. An additional 3,000 acres (1,200 ha) was subsequently acquired. About 1,000 families were affected by the order, which came into effect on 7 October.[80] Protests, legal appeals, and a 1943 Congressional inquiry were to no avail.[81] By mid-November U.S. Marshals were posting notices to vacate on farmhouse doors, and construction contractors were moving in.[82] Some families were given two weeks' notice to vacate farms that had been their homes for generations.[83] The ultimate cost of the land acquisition, which was not completed until March 1945, was only about $2.6 million—around $47 an acre.[84] When presented with a proclamation declaring Oak Ridge a total exclusion area that no one could enter without military permission, the Governor of Tennessee, Prentice Cooper, angrily tore it up.[85]
Initially known as the Kingston Demolition Range, the site was officially renamed the
Los Alamos
The idea of locating Project Y at Oak Ridge was considered, but it was decided that it should be in a remote location. On Oppenheimer's recommendation, the search for a suitable site was narrowed to the vicinity of Albuquerque, New Mexico, where Oppenheimer owned a ranch.[91] On 16 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, which, it was hoped, would inspire those working on the project.[92][93] The engineers were concerned about the poor access road, and whether the water supply would be adequate, but otherwise felt that it was ideal.[94]
Patterson approved the acquisition of the site on 25 November 1942, authorizing $440,000 for the purchase of 54,000 acres (22,000 ha), all but 8,900 acres (3,600 ha) of which were already owned by the Federal Government.
During the war, Los Alamos was referred to as "Site Y" or "the Hill".
Chicago
An Army-OSRD council on 25 June 1942 decided to build a
Delays in establishing the plant at Argonne led Compton to authorize the Metallurgical Laboratory to construct the first nuclear reactor beneath the bleachers of Stagg Field at the University of Chicago. The reactor required an enormous amount of highly purified graphite blocks and uranium in both metallic and powdered oxide forms. At the time, there was a limited source of pure uranium metal; Frank Spedding of Iowa State University was able to produce only two short tons. Three short tons was supplied by Westinghouse Lamp Plant, produced in a rush with makeshift process. A large square balloon was constructed by Goodyear Tire to encase the reactor.[103][104]
On 2 December 1942, a team led by Enrico Fermi initiated the first artificial[d] self-sustaining nuclear chain reaction in an experimental reactor known as Chicago Pile-1.[106] The point at which a reaction becomes self-sustaining became known as "going critical". Compton reported the success to Conant in Washington, D.C., by a coded phone call, saying, "The Italian navigator [Fermi] has just landed in the new world."[107][e]
In January 1943, Grafton's successor, Major Arthur V. Peterson, ordered Chicago Pile-1 dismantled and reassembled at the Argonne Forest site, as he regarded the operation of a reactor as too hazardous for a densely populated area.[108] The new site, still operated by the Metallurgical Laboratory, became known as 'Site A'. Chicago Pile-3, the first heavy water reactor, also went critical at this site, on 15 May 1944.[109][110] After the war, operations at Site A were moved about 6 miles (9.7 km) to DuPage County, the current location of the Argonne National Laboratory.[102]
Hanford
By December 1942 there were concerns that even Oak Ridge was too close to a major population center (Knoxville) in the unlikely event of a major nuclear accident. Groves recruited DuPont in November 1942 to be the prime contractor for the construction of the plutonium production complex. The President of the company, Walter S. Carpenter Jr., wanted no profit of any kind; for legal reasons a nominal fee of one dollar was agreed upon.[111]
DuPont recommended that the site be located far from the existing uranium production facility at Oak Ridge.[112] In December 1942, Groves dispatched Colonel Franklin Matthias and DuPont engineers to scout potential sites. Matthias reported that Hanford Site near Richland, Washington, was "ideal in virtually all respects". It was isolated and near the Columbia River, which could supply sufficient water to cool the reactors. Groves visited the site in January and established the Hanford Engineer Works (HEW), codenamed "Site W".[113]
Under Secretary Patterson gave his approval on 9 February, allocating $5 million for the acquisition of 430,000 acres (170,000 ha). The federal government relocated some 1,500 residents of nearby settlements, as well as the Wanapum and other tribes using the area. A dispute arose with farmers over compensation for crops, which had already been planted. Where schedules allowed, the Army allowed the crops to be harvested, but this was not always possible.[113] The land acquisition process dragged on and was not completed before the end of the Manhattan Project in December 1946.[114]
The dispute did not delay work. Although progress on the reactor design at Metallurgical Laboratory and DuPont was not sufficiently advanced to accurately predict the scope of the project, a start was made in April 1943 on facilities for an estimated 25,000 workers, half of whom were expected to live on-site. By July 1944, some 1,200 buildings had been erected and nearly 51,000 people were living in the construction camp. As area engineer, Matthias exercised overall control of the site.[115] At its peak, the construction camp was the third most populous town in Washington state.[116] Hanford operated a fleet of over 900 buses, more than the city of Chicago.[117] Like Los Alamos and Oak Ridge, Richland was a gated community with restricted access, but it looked more like a typical wartime American boomtown: the military profile was lower, and physical security elements like high fences and guard dogs were less evident.[118]
Canadian sites
British Columbia
Ontario
The
Northwest Territories
The Eldorado Mine at Port Radium was a source of uranium ore.[121]
Heavy water sites
Although DuPont's preferred designs for the nuclear reactors were helium cooled and used graphite as a moderator, DuPont still expressed an interest in using heavy water as a backup. The
Uranium
Ore
The key raw material for the project was uranium, which was used as fuel for the reactors, as feed that was transformed into plutonium, and, in its enriched form, in the atomic bomb itself. There were four known major deposits of uranium in 1940: in Colorado, in northern Canada, in
Of these ores, those from the Belgian Congo contained the most uranium per mass of rock by far.
The raw ore was dissolved in
Isotope separation
Natural uranium consists of 99.3% uranium-238 and 0.7% uranium-235, but as only the latter is
Centrifuges
The centrifuge process was regarded as the only promising separation method in April 1942.[139] Jesse Beams had developed such a process in the 1930s, but had encountered technical difficulties. In 1941 he began working with uranium hexafluoride, the only known gaseous compound of uranium, and was able to separate uranium-235. At Columbia, Karl P. Cohen produced a body of mathematical theory making it possible to design a centrifugal separation unit, which Westinghouse undertook to construct.[140]
Scaling this up to a production plant presented a formidable technical challenge. Urey and Cohen estimated that producing a kilogram (2.2 lb) of uranium-235 per day would require up to 50,000 centrifuges with 1-meter (3 ft 3 in) rotors, or 10,000 centrifuges with 4-meter (13 ft) rotors, assuming that 4-meter rotors could be built. The prospect of keeping so many rotors operating continuously at high speed appeared daunting,[141] and when Beams ran his experimental apparatus, he obtained only 60% of the predicted yield, indicating that more centrifuges were required. Beams, Urey and Cohen then began work on a series of improvements which promised to increase efficiency. However, frequent failures of motors, shafts and bearings at high speeds delayed work on the pilot plant.[142]
In November 1942 the centrifuge process was abandoned by the Military Policy Committee.[143] Successful gas centrifuges of the Zippe-type design were instead developed in the Soviet Union after the war. It eventually became the preferred method of uranium isotope separation, being far more economical.[144]
Electromagnetic separation
Electromagnetic isotope separation was developed at the University of California Radiation Laboratory. This method employed devices known as calutrons. The name was derived from the words California, university and cyclotron.[145] In the electromagnetic process, a magnetic field deflected charged particles according to mass.[146] The process was neither scientifically elegant nor industrially efficient.[147] Compared with a gaseous diffusion plant or a nuclear reactor, an electromagnetic separation plant would consume more scarce materials, require more manpower to operate, and cost more to build. Nonetheless, the process was approved because it was based on proven technology and therefore represented less risk. Moreover, it could be built in stages, and rapidly reach industrial capacity.[145]
Marshall and Nichols discovered that the electromagnetic isotope separation process would require 5,000 short tons (4,500 tonnes) of copper, which was in desperately short supply. However, silver could be substituted, in an 11:10 copper to silver ratio. On 3 August 1942, Nichols met with
Responsibility for the design and construction of the electromagnetic separation plant, which came to be called
The calutrons initially enriched the uranium-235 content to between 13% and 15%, and shipped the first few hundred grams of this to Los Alamos in March 1944. Only 1 part in 5,825 of the uranium feed emerged as product. Much of the rest was splattered over equipment in the process. Strenuous recovery efforts helped raise production to 10% of the uranium-235 feed by January 1945. In February the Alpha racetracks began receiving slightly enriched (1.4%) feed from the new S-50 thermal diffusion plant, and the next month they received enhanced (5%) feed from the K-25 gaseous diffusion plant. By August, K-25 was producing uranium sufficiently enriched to feed directly into the Beta tracks.[156]
Gaseous diffusion
The most promising but also the most challenging method of isotope separation was gaseous diffusion. Graham's law states that the rate of effusion of a gas is inversely proportional to the square root of its molecular mass, so in a box containing a semi-permeable membrane and a mixture of two gases, the lighter molecules will pass out of the container more rapidly than the heavier molecules. The idea was that such boxes could be formed into a cascade of pumps and membranes, with each successive stage containing a slightly more enriched mixture. Research into the process was carried out at Columbia University by a group that included Harold Urey, Karl P. Cohen, and John R. Dunning.[157]
In November 1942 the Military Policy Committee approved the construction of a 600-stage gaseous diffusion plant.
Kellex's design for K-25 called for a four-story 0.5-mile (0.80 km) long U-shaped structure containing 54 contiguous buildings. These were divided into nine sections containing cells of six stages. A survey party began construction by marking out the 500-acre (2.0 km2) site in May 1943. Work on the main building began in October 1943, and the six-stage pilot plant was ready for operation on 17 April 1944. In 1945 Groves canceled the upper stages, directing Kellex to instead design and build a 540-stage side feed unit, which became known as K-27. Kellex transferred the last unit to the operating contractor, Union Carbide and Carbon, on 11 September 1945. The total cost, including the K-27 plant completed after the war, came to $480 million.[162]
The production plant commenced operation in February 1945, and as cascade after cascade came online, the quality of the product increased. By April 1945, K-25 had attained a 1.1% enrichment, and the output of the S-50 thermal diffusion plant began being used as feed. Some product produced the next month reached nearly 7% enrichment. In August, the last of the 2,892 stages commenced operation. K-25 and K-27 achieved their full potential in the early postwar period, when they eclipsed the other production plants and became the prototypes for a new generation of plants.[163]
Thermal diffusion
The thermal diffusion process was based on
Groves contracted with the H. K. Ferguson Company of Cleveland, Ohio, to build the thermal diffusion plant, which was designated S-50.[167] Plans called for the installation of 2,142 48-foot-tall (15 m) diffusion columns arranged in 21 racks. Inside each column were three concentric tubes. Steam, obtained from the nearby K-25 powerhouse at a pressure of 100 pounds per square inch (690 kPa) and temperature of 545 °F (285 °C), flowed downward through the innermost 1.25-inch (32 mm) nickel pipe, while water at 155 °F (68 °C) flowed upward through the outermost iron pipe. The uranium hexafluoride flowed in the middle copper pipe, and isotope separation of the uranium occurred between the nickel and copper pipes.[168] Work commenced on 9 July 1944, and S-50 began partial operation in September. Leaks limited production and forced shutdowns over the next few months, but in June 1945 the S-50 plant produced 12,730 pounds (5,770 kg) of slightly enriched product.[169]
By March 1945, all 21 production racks were operating. Initially the output of S-50 was fed into Y-12, but starting in March 1945 all three enrichment processes were run in series. S-50 became the first stage, enriching the uranium from 0.71% to 0.89% uranium-235. This was then fed into the gaseous diffusion process in the K-25 plant, which produced a product enriched to about 23%. In turn, this was fed into Y-12,[170] which boosted it to about 89%, sufficient for use in nuclear weapons. About 50 kilograms (110 lb) of uranium enriched to 89% was delivered to Los Alamos by July 1945. The entire 50 kg, along with some 50%-enriched, averaging out to about 85% enriched, were used in the first Little Boy bomb.[171]
Plutonium
The second line of development pursued by the Manhattan Project used plutonium. Although small amounts of plutonium exist in nature, the best way to obtain large quantities is via a reactor. Natural uranium is bombarded by neutrons and
X-10 Graphite Reactor
In March 1943, DuPont began construction of a plutonium plant on a 112-acre (0.5 km2) site at Oak Ridge. Intended as a pilot plant for the larger production facilities at Hanford, it included the air-cooled X-10 Graphite Reactor, a chemical separation plant, and support facilities. Because of the subsequent decision to construct water-cooled reactors at Hanford, only the chemical separation plant operated as a true pilot.[173] The X-10 Graphite Reactor consisted of a huge block of graphite, 24 feet (7.3 m) per side, weighing around 1,500 short tons (1,400 t), surrounded by 7 feet (2.1 m) of high-density concrete as a radiation shield.[173]
The greatest difficulty was encountered with the uranium slugs produced by Mallinckrodt and Metal Hydrides. These had to be coated in aluminum to avoid corrosion and the escape of fission products into the cooling system. The Grasselli Chemical Company attempted to develop a hot dipping process without success. Alcoa tried canning, developing a new process for flux-less welding; 97% of the cans passed a standard vacuum test, but high temperature tests indicated a failure rate of more than 50%. Nonetheless, production began in June 1943. The Metallurgical Laboratory eventually developed an improved welding technique with the help of General Electric, which was incorporated into the production process in October 1943.[174]
The X-10 Graphite Reactor went critical on 4 November 1943 with about 30 short tons (27 t) of uranium. A week later the load was increased to 36 short tons (33 t), raising its power generation to 500 kW, and by the end of the month the first 500 mg of plutonium was created.[175] Gradual modifications raised the power to 4,000 kW in July 1944. X-10 operated as a production plant until January 1945, when it was turned over to research.[176]
Hanford reactors
Although an air-cooled design was chosen for the reactor at Oak Ridge to facilitate rapid construction, this was impractical for the much larger production reactors. Initial designs by the Metallurgical Laboratory and DuPont used helium for cooling, before they determined that a water-cooled reactor was simpler, cheaper and quicker to build.[177] The design did not become available until 4 October 1943; in the meantime, Matthias concentrated on improving the Hanford Site by erecting accommodations, improving the roads, building a railway switch line, and upgrading the electricity, water and telephone lines.[178]
As at Oak Ridge, the most difficulty was encountered while canning the uranium slugs, which commenced at Hanford in March 1944. They were
Work began on Reactor B, the first of six planned 250 MW reactors, on 10 October 1943.[180] The reactor complexes were given letter designations A through F, with B, D and F sites developed first, as this maximized the distance between the reactors. They were the only ones constructed during the Manhattan Project.[181] Some 390 short tons (350 t) of steel, 17,400 cubic yards (13,300 m3) of concrete, 50,000 concrete blocks and 71,000 concrete bricks were used to construct the 120-foot (37 m) high building.
Construction of the reactor itself commenced in February 1944.[182] Watched by Compton, Matthias, DuPont's Crawford Greenewalt, Leona Woods and Fermi, who inserted the first slug, the reactor was powered up beginning on 13 September 1944. Over the next few days, 838 tubes were loaded and the reactor went critical. Shortly after midnight on 27 September, the operators began to withdraw the control rods to initiate production. At first all appeared well but around 03:00 the power level started to drop and by 06:30 the reactor had shut down completely. The cooling water was investigated to see if there was a leak or contamination. The next day the reactor started up again, only to shut down once more.[183][184]
Fermi contacted Chien-Shiung Wu, who identified the cause of the problem as neutron poisoning from xenon-135, which has a half-life of 9.2 hours.[185] Fermi, Woods, Donald J. Hughes and John Archibald Wheeler then calculated the nuclear cross section of xenon-135, which turned out to be 30,000 times that of uranium.[186] DuPont engineer George Graves had deviated from the Metallurgical Laboratory's original design in which the reactor had 1,500 tubes arranged in a circle, and had added an additional 504 tubes to fill in the corners. The scientists had originally considered this overengineering a waste of time and money, but Fermi realized that by loading all 2,004 tubes, the reactor could reach the required power level and efficiently produce plutonium.[187] Reactor D was started on 17 December 1944 and Reactor F on 25 February 1945.[188]
Separation process
Meanwhile, the chemists considered how plutonium could be separated from uranium when its chemical properties were not known. Working with the minute quantities of plutonium available at the Metallurgical Laboratory in 1942, a team under Charles M. Cooper developed a lanthanum fluoride process which was chosen for the pilot separation plant. A second separation process, the bismuth phosphate process, was subsequently developed by Seaborg and Stanly G. Thomson.[189] Greenewalt favored the bismuth phosphate process due to the corrosive nature of lanthanum fluoride, and it was selected for the Hanford separation plants.[190] Once X-10 began producing plutonium, the pilot separation plant was put to the test. The first batch was processed at 40% efficiency but over the next few months this was raised to 90%.[176]
At Hanford, top priority was initially given to the installations in the 300 area: buildings for testing materials, preparing uranium, and assembling and calibrating instrumentation. One of the buildings housed the canning equipment for the uranium slugs, while another contained a small test reactor. Notwithstanding its priority, work on the 300 area fell behind schedule due to the unique and complex nature of the facilities, and wartime shortages of labor and materials.[191]
Early plans called for the construction of two separation plants in each of the areas known as 200-West and 200-East. This was subsequently reduced to two, the T and U plants, in 200-West and one, the B plant, at 200-East.[192] Each separation plant consisted of four buildings: a process cell building or "canyon" (known as 221), a concentration building (224), a purification building (231) and a magazine store (213). The canyons were each 800 feet (240 m) long and 65 feet (20 m) wide. Each consisted of forty 17.7-by-13-by-20-foot (5.4 by 4.0 by 6.1 m) cells.[193]
Work began on 221-T and 221-U in January 1944, with the former completed in September and the latter in December. The 221-B building followed in March 1945. Because of the high levels of radioactivity involved, work in the separation plants had to be conducted by remote control using closed-circuit television, something unheard of in 1943. Maintenance was carried out with the aid of an overhead crane and specially designed tools. The 224 buildings were smaller because they had less material to process, and it was less radioactive. The 224-T and 224-U buildings were completed on 8 October 1944, and 224-B followed on 10 February 1945. The purification methods that were eventually used in 231-W were still unknown when construction commenced on 8 April 1944, but the plant was complete and the methods were selected by the end of the year.[194] On 5 February 1945, Matthias hand-delivered the first shipment of 80 g of 95%-pure plutonium nitrate to a Los Alamos courier in Los Angeles.[188]
Weapon design
In 1943, development efforts were directed to a gun-type fission weapon with plutonium called Thin Man. Initial research on the properties of plutonium was done using cyclotron-generated plutonium-239, which was extremely pure but could only be created in very small amounts. Los Alamos received the first sample of plutonium from the Clinton X-10 reactor in April 1944 and within days Emilio Segrè discovered a problem: the reactor-bred plutonium had a higher concentration of plutonium-240, resulting in up to five times the spontaneous fission rate of cyclotron plutonium.[195]
This rendered it unsuitable for use in a gun-type weapon, for the plutonium-240 would start the chain reaction too soon, causing a
Work on an alternative method of bomb design, known as implosion, had begun earlier under the direction of the physicist 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. When the fissile atoms are packed closer together, the rate of neutron capture increases,[197] so it also makes more efficient use of fissionable material.[198] Neddermeyer's 1943 and early 1944 investigations showed promise, but also made it clear that an implosion weapon was more complex than the gun-type design from both a theoretical and an engineering perspective.[199] In September 1943, John von Neumann, who had experience with shaped charges, proposed using a spherical configuration instead of the cylindrical one that Neddermeyer was working on.[200]
An accelerated effort on the implosion design, codenamed Fat Man, began in August 1944 when Oppenheimer implemented a sweeping reorganization of the Los Alamos laboratory to focus on implosion.[201] Two new groups were created at Los Alamos to develop the implosion weapon, X (for explosives) Division headed by explosives expert George Kistiakowsky and G (for gadget) Division under Robert Bacher.[202][203] The new design featured explosive lenses that focused the implosion into a spherical shape.[204] The design of lenses turned out to be slow, difficult and frustrating.[204] Various explosives were tested before settling on composition B and baratol.[205] The final design resembled a soccer ball, with 20 hexagonal and 12 pentagonal lenses, each weighing about 80 pounds (36 kg). Getting the detonation just right required fast, reliable and safe electrical detonators, of which there were two for each lens for reliability.[206] They used exploding-bridgewire detonators, a new invention developed at Los Alamos by a group led by Luis Alvarez.[207]
To study the behavior of converging
Within the explosives was an aluminum pusher, which provided a smooth transition from the relatively low-density explosive to the next layer, the
The ultimate task of the metallurgists was to determine how to cast plutonium into a sphere. The difficulties became apparent when attempts to measure the density of plutonium gave inconsistent results. At first contamination was suspected, but it was soon determined that there were multiple
The work proved dangerous. By the end of the war, half the chemists and metallurgists had to be removed from work with plutonium when unacceptably high levels of the element was detected in their urine.[216] A minor fire at Los Alamos in January 1945 led to a fear that a fire in the plutonium laboratory might contaminate the whole town, and Groves authorized the construction of a new facility for plutonium chemistry and metallurgy, which became known as the DP-site.[217] The hemispheres for the first plutonium pit (or core) were produced and delivered on 2 July 1945. Three more hemispheres followed on 23 July and were delivered three days later.[218]
In contrast to the plutonium Fat Man, the uranium gun-type Little Boy weapon was straightforward if not trivial to design. Overall responsibility for it was assigned to Parsons's Ordnance (O) Division, with the design, development, and technical work at Los Alamos consolidated under
Research into the Super was also pursued, although it was considered secondary to the development of a fission bomb. The effort was directed by Teller, who was its most enthusiastic proponent.[221] The F-1 (Super) Group calculated that burning 1 cubic meter (35 cu ft) of liquid deuterium would release the energy of 10 megatonnes of TNT (42 PJ), enough to devastate 1,000 square miles (2,600 km2).[222] In a final report on the Super in June 1946, Teller remained upbeat about the prospect of it being successfully developed, although that opinion was not universal.[223]
Trinity
Because of the complexity of an implosion-style weapon, it was decided that, despite the waste of fissile material, a full-scale
Groves did not relish the prospect of explaining to a Senate committee the loss of a billion dollars worth of plutonium, so a cylindrical containment vessel codenamed "Jumbo" was constructed to recover the active material in the event of a failure. It was fabricated at great expense from 214 short tons (194 t) of iron and steel.[229] By the time it arrived, however, confidence in the implosion method was high enough, and the availability of plutonium was sufficient, that Oppenheimer decided not to use it. Instead, it was placed atop a steel tower 800 yards (730 m) from the weapon as a rough measure of the explosion's power. Jumbo survived, although its tower did not, adding credence to the belief that Jumbo would have successfully contained a fizzled explosion.[230][227]
For the actual test, the weapon, nicknamed "the gadget", was hoisted to the top of a 100-foot (30 m) steel tower, as detonation at that height would give a better indication of how the weapon would behave when dropped from a bomber. Detonation in the air maximized the energy applied directly to the target and generated less nuclear fallout. The gadget was assembled under the supervision of Norris Bradbury at the nearby McDonald Ranch House on 13 July, and precariously winched up the tower the following day.[231]
At 05:30 on 16 July 1945 the gadget exploded with an energy equivalent of around 20 kilotons of TNT, leaving a crater of Trinitite (radioactive glass) in the desert 250 feet (76 m) wide. The shock wave was felt over 100 miles (160 km) away, and the mushroom cloud reached 7.5 miles (12.1 km) in height. It was heard as far away as El Paso, Texas, so Groves issued a cover story about an ammunition magazine explosion at Alamogordo Field involving gas shells.[232][233]
Oppenheimer later claimed that, while witnessing the explosion, he thought of a verse from the
कालोऽस्मि लोकक्षयकृत्प्रवृद्धो लोकान्समाहर्तुमिह प्रवृत्तः। ऋतेऽपि त्वां न भविष्यन्ति सर्वे येऽवस्थिताः प्रत्यनीकेषु योधाः॥११- ३२॥ |
together with verse (XI,32), which he translated as "Now I am become Death, destroyer of worlds".[236][237][h]
The test was significantly more successful than had been anticipated; this was immediately cabled to Stimson, who was then at the Potsdam Conference, and Groves hastily prepared a lengthier report sent via courier. Truman was powerfully and positively affected by the news. Stimson noted in his diary that when he shared it with Churchill, Churchill remarked: "Now I know what happened to Truman yesterday. I couldn't understand it. When he got to the meeting after having read this report, he was a changed man. He told the Russians just where they got on and off and generally bossed the whole meeting."[239]
Personnel
At its peak in June 1944, the Manhattan Project employed about 129,000 workers, of whom 84,500 were construction workers, 40,500 were plant operators and 1,800 were military personnel. As construction activity declined, the workforce fell to 100,000 a year later, but the number of military personnel increased to 5,600. Procuring the required numbers of workers, especially highly skilled workers, in competition with other vital wartime programs proved very difficult.[240] Due to high turnover, over 500,000 people worked on the project.[241] Most African Americans were employed in low-level jobs, but there were a few African-American scientists and technicians.[242]
In 1943, Groves obtained a special temporary priority for labor from the War Manpower Commission. In March 1944, both the War Production Board and the War Manpower Commission gave the project their highest priority.[243] The Kansas commission director stated that from April to July 1944 every qualified applicant in the state who visited a United States Employment Service office was urged to work at the Hanford Site. No other job was offered until the applicant definitively rejected the offer.[244] Tolman and Conant, in their role as the project's scientific advisers, drew up a list of candidate scientists and had them rated by scientists already working on the project. Groves then sent a personal letter to the head of their university or company asking for them to be released for essential war work.[245]
One source of skilled personnel was the Army itself, particularly the Army Specialized Training Program. In 1943, the MED created the Special Engineer Detachment (SED), with an authorized strength of 675. Technicians and skilled workers drafted into the Army were assigned to the SED. Another source was the Women's Army Corps (WAC). Initially intended for clerical tasks handling classified material, the WACs were soon tapped for technical and scientific tasks as well.[246] On 1 February 1945, all military personnel assigned to the MED, including all SED detachments, were assigned to the 9812th Technical Service Unit, except at Los Alamos, where military personnel other than SED, including the WACs and Military Police, were assigned to the 4817th Service Command Unit.[247]
An associate professor of
Secrecy
The Manhattan Project operated under a mandate of "absolute secrecy" from Roosevelt, meaning that the very existence of the project itself was to be kept secret. This proved a daunting task given the amount of knowledge and speculation about nuclear fission that existed prior to the Manhattan Project, the huge numbers of people involved, and the scale of the facilities.
Compartmentalization of knowledge, to me, was the very heart of security. My rule was simple and not capable of misinterpretation—each man should know everything he needed to know to do his job and nothing else. Adherence to this rule not only provided an adequate measure of security, but it greatly improved over-all efficiency by making our people stick to their knitting. And it made quite clear to all concerned that the project existed to produce a specific end product—not to enable individuals to satisfy their curiosity and to increase their scientific knowledge.[252]
This clashed with the norms of many of the scientists involved, who claimed that science could not operate successfully under such requirements. The Manhattan Project officials also had difficulty with journalists, Congressmen, federal officials who were not "in the know", residents near local sites, judges adjudicating land claims, and other sources of speculation, prying, and leaks, along with concerns about
Because of its relative success at keeping the story out of newspapers, Byron Price, head of the Office of Censorship, ultimately designated the Manhattan Project "the best-kept secret of the war".[253] In 1945 Life estimated that before the Hiroshima and Nagasaki bombings "probably no more than a few dozen men in the entire country knew the full meaning of the Manhattan Project, and perhaps only a thousand others even were aware that work on atoms was involved." The magazine wrote that the more than 100,000 others employed with the project "worked like moles in the dark". Warned that disclosing the project's secrets was punishable by 10 years in prison or a fine of US$10,000 (equivalent to $169,000 in 2023), they monitored "dials and switches while behind thick concrete walls mysterious reactions took place" without knowing the purpose of their jobs.[254][255][256]
In December 1945 the US Army published a secret report assessing the security apparatus surrounding the Manhattan Project. The report states that the project was "more drastically guarded than any other highly secret war development." The surrounding security infrastructure was so vast and thorough that in the early days of the project in 1943, investigators vetted 400,000 potential employees and 600 companies for potential security risks.[257]
Censorship
Voluntary censorship of atomic information began before the Manhattan Project. After the start of the European war in 1939 American scientists began avoiding publishing military-related research, and in 1940 scientific journals began asking the National Academy of Sciences to clear articles. William L. Laurence of The New York Times, who wrote an article on atomic fission in The Saturday Evening Post of 7 September 1940, later learned that government officials asked librarians nationwide in 1943 to withdraw the issue.[258] The Soviets noticed the silence, however. In April 1942 nuclear physicist Georgy Flyorov wrote to Joseph Stalin on the absence of articles on nuclear fission in American journals; this resulted in the Soviet Union establishing its own atomic bomb project.[259]
The Manhattan Project operated under tight security lest its discovery induce Axis powers, especially Germany, to accelerate their own nuclear projects or undertake covert operations against the project.[260] The Office of Censorship relied on the press to comply with a voluntary code of conduct it published, and the project at first avoided notifying the office. By early 1943 newspapers began publishing reports of large construction in Tennessee and Washington, and the office began discussing with the project how to maintain secrecy. In June it asked newspapers and broadcasters to avoid discussing "atom smashing, atomic energy, atomic fission, atomic splitting, or any of their equivalents. The use for military purposes of radium or radioactive materials, heavy water, high voltage discharge equipment, cyclotrons."[261][253]
Soviet spies
The prospect of sabotage was always present, and sometimes suspected when there were equipment failures. While there were some problems believed to be the result of careless or disgruntled employees, there were no confirmed instances of Axis-instigated sabotage.
The most successful Soviet spy was Klaus Fuchs, a physicist and member of the British Mission who was intimately involved in work at Los Alamos on the design of the implosion bomb.[266] His espionage activities were not identified until 1950, as a result of Venona project. The revelation of his espionage activities damaged the United States' nuclear cooperation with Britain and Canada,[267] and other instances of espionage were subsequently uncovered, leading to the arrest of Harry Gold, David Greenglass, and Julius and Ethel Rosenberg.[268] Other spies like George Koval and Theodore Hall remained unknown for decades.[269] The value of the espionage is difficult to quantify, as the principal constraint on the Soviet atomic bomb project was their short supply of uranium ore. It may have saved the Soviets at least one or two years in the development of their own bomb,[270] although some historians have argued the Soviets spent as much time vetting and reduplicating the information as they would have saved had they trusted it.[271]
Foreign intelligence
In addition to developing the atomic bomb, the Manhattan Project was charged with gathering intelligence on the
The Alsos Mission to Italy questioned physics laboratory staff at the
Following in the wake of the advancing Allied armies, Pash and Calvert interviewed
Alsos teams rounded up German scientists including
Atomic bombings of Hiroshima and Nagasaki
Preparations
The only Allied aircraft capable of carrying the 17-foot (5.2 m) long Thin Man or the 59-inch (150 cm) wide Fat Man was the British
The
At the end of December 1944, worried by the heavy losses occurring in the Battle of the Bulge, Roosevelt instructed Groves and Stimson that if the atomic bombs were ready before the war with Germany ended, they should be ready to drop them on Germany, but Japan was regarded as more likely.[291] In late April 1945, a targeting committee was established to determine which cities should be targets, and it recommended Kokura, Hiroshima, Niigata, and Kyoto. Stimson intervened, announcing that he would be making the targeting decision, and that he would not authorize the bombing of Kyoto on the grounds of its historical and religious significance.[292] Nagasaki was ultimately substituted.[293] In May 1945, the Interim Committee was created to advise on wartime and postwar use of nuclear energy. The Interim Committee in turn established a scientific panel consisting of Arthur Compton, Fermi, Lawrence, and Oppenheimer; the scientific panel offered its opinion not just on the likely physical effects of an atomic bomb, but on its probable military and political impact. In a meeting on 1 June, the Interim Committee resolved that "the bomb should be used against Japan as soon as possible; that it be used on a war plant surrounded by workers' homes; and that it be used without prior warning".[294][295]
At the Potsdam Conference in Germany, President Harry S. Truman told Stalin, the leader of the Soviet Union, that the US had "a new weapon of unusual destructive force", without giving any details. As he showed "no special interest," Truman erroneously assumed that Stalin did not understand. In reality, Soviet spies had kept Stalin informed of the work and the planned test.[296][297][298]
A strike order from General Thomas T. Handy to General Carl Spaatz was approved by Marshall and Stimson on 25 July. It ordered that the "first special bomb" be used "after about 3 August 1945." It indicated that "additional bombs will be delivered on the above targets as soon as made ready by the project staff".[299]
Bombings
On 6 August 1945, the
On the morning of 9 August 1945, the
Groves expected to have another atomic bomb ready for use on 19 August, with three more in September and a further three in October.[309] Two more Fat Man assemblies were readied, and scheduled to leave Kirtland Field for Tinian on 11 and 14 August.[308] At Los Alamos, technicians worked 24 hours straight to cast another plutonium core.[310] Although cast, it still needed to be pressed and coated, which would take until 16 August.[311] It could therefore have been ready for use on 19 August.
On 10 August, Truman was informed that another bomb was being prepared. He ordered that no additional atomic bombs could be used without his express authority.
On 11 August, Groves phoned Warren with orders to organize a survey team to report on the damage and radioactivity at Hiroshima and Nagasaki as soon as the war ended. A party equipped with portable Geiger counters arrived in Hiroshima on 8 September headed by Farrell and Warren, with Japanese Rear Admiral Masao Tsuzuki, who acted as a translator. They remained in Hiroshima until 14 September and then surveyed Nagasaki from 19 September to 8 October.[314] This and other scientific missions to Japan provided valuable data on the effects of the atomic bomb, and led to the creation of the Atomic Bomb Casualty Commission.[315]
In anticipation of the bombings, Groves had commissioned physicist Henry DeWolf Smyth to prepare a sanitized technical history of the project for public consumption. The idea of releasing such information freely was controversial, and the ultimate decision to do so was made by Truman personally. The "Smyth Report" was released to the public on 12 August 1945.[316]
After the war
The Manhattan Project became instantly famous after the bombing of Hiroshima and the partial lifting of its secrecy. It was widely credited with ending the war, and Groves worked to credit its contractors, whose work had hitherto been secret. Groves and Nichols presented them with
The Manhattan Project persisted until 31 December 1946, and the Manhattan District to 15 August 1947.[322] During this time, it suffered from numerous difficulties caused by technical problems, the effects of rapid demobilization, and a lack of clarity on its long-term mission.
At Hanford, plutonium production declined as Reactors B, D and F wore out, poisoned by fission products and swelling of the graphite moderator known as the Wigner effect. The swelling damaged the charging tubes where the uranium was irradiated to produce plutonium, rendering them unusable. Production was curtailed and the oldest unit, B pile, was closed down so at least one reactor would remain available. Research continued, with DuPont and the Metallurgical Laboratory developing a redox solvent extraction process as an alternative plutonium extraction technique to the bismuth phosphate process, which left unspent uranium in a state from which it could not easily be recovered.[323]
Bomb engineering was carried out by the Z Division,[324] initially located at Wendover Field but moved to Oxnard Field, New Mexico, in September 1945 to be closer to Los Alamos. This marked the beginning of the Sandia Base. Nearby Kirtland Field was used as a B-29 base for aircraft compatibility and drop tests.[325] As reservist officers were demobilized, they were replaced by about fifty hand-picked regular officers.[326]
Nichols recommended that S-50 and the Alpha tracks at Y-12 be closed down. This was done in September.[327] Although performing better than ever,[328] the Alpha tracks could not compete with K-25 and the new K-27, which had commenced operation in January 1946. In December, the Y-12 plant was closed, cutting the Tennessee Eastman payroll from 8,600 to 1,500 and saving $2 million a month.[329]
Nowhere was demobilization more of a problem than at Los Alamos, where there was an exodus of talent. Much remained to be done. The bombs used on Hiroshima and Nagasaki needed work to make them simpler, safer and more reliable. Implosion methods needed to be developed for uranium in place of the wasteful gun method, and composite uranium-plutonium cores were needed now that plutonium was in short supply. However, uncertainty about the future of the laboratory made it hard to induce people to stay. Oppenheimer returned to his job at the University of California and Groves appointed Norris Bradbury as an interim replacement; Bradbury remained in the post for the next 25 years.[330] Groves attempted to combat the dissatisfaction caused by the lack of amenities with a construction program that included an improved water supply, three hundred houses, and recreation facilities.[323]
Two Fat Man-type detonations were conducted at Bikini Atoll in July 1946 as part of Operation Crossroads to investigate the effect of nuclear weapons on warships.[331] Able was detonated on 1 July 1946. The more spectacular Baker was detonated underwater on 25 July 1946.[332] Following a domestic debate over the permanent management of the nuclear program, the Atomic Energy Act of 1946 created the United States Atomic Energy Commission to take over the functions and assets of the project. It established civilian control over atomic development, and separated the development, production and control of atomic weapons from the military. Military aspects were taken over by the Armed Forces Special Weapons Project (AFSWP).[333]
After the bombings at Hiroshima and Nagasaki, a number of Manhattan Project physicists founded the
Cost
Site | Cost (1945 USD, millions) | Cost (2023 USD, millions) | % of total |
---|---|---|---|
Oak Ridge | $1,188 | $15,949 | 62.9% |
Hanford | $390 | $5,236 | 20.6% |
Special operating materials | $103 | $1,387 | 5.5% |
Los Alamos | $74 | $994 | 3.9% |
Research and development | $70 | $935 | 3.7% |
Government overhead | $37 | $500 | 2.0% |
Heavy water plants | $27 | $359 | 1.4% |
Total | $1,890 | $25,361 |
The project expenditure through 1 October 1945 was $1.845 billion, equivalent to less than nine days of wartime spending, and was $2.191 billion when the AEC assumed control on 1 January 1947. The total allocation was $2.4 billion. 84% of the costs through the end of 1945 were spent on the plants at Oak Ridge and Hanford, producing the enriched uranium and plutonium needed to fuel the bombs. At both sites, the majority of the costs were for construction (74% at Oak Ridge, 87% at Hanford), with the rest being for operations.[337][338][339]
Initial funding for the project was through the general budget of the Office of Scientific Research and Development. As plans were made to turn the work over to the Army Corps of Engineers, Bush wrote to Roosevelt in late 1942 that "it would be ruinous to the essential secrecy to have to defend before an appropriations committee any request for funds for this project." Instead, initial funding was done through discretionary funds to which Roosevelt had access.[340]
As it grew in size and cost, Congress was deliberately kept ignorant of the project, because of concerns that Congressmen were prone to leaking information, and because it was feared that the project would appear to be a boondoggle. Appropriations requests were quietly slipped into other bills, but the project's mounting costs and large facilities (which appeared to many to produce nothing) attracted scrutiny from several Congressional auditors. The Truman Committee that investigated wartime waste and fraud attempted to audit the project several times, but each time their inquiries were rejected.[341]
These Congressional inquiries, along with the need for smooth budgetary approval, led to Bush, Groves, and Stimson agreeing in the spring of 1944 that a few high-ranking Congressmen should be told of the project's purpose. By March 1945, exactly seven Congressmen were officially informed.[341] The funds were hidden into appropriation requests with the inconspicuous headings, frequently "Engineer Service Army" and "Expediting Production." In late May 1945, to further expedite budget issues and assure the cooperation of Albert J. Engel, who had threatened to reveal the existence of the project if he was not told more about it, five additional Congressmen were permitted to visit the Oak Ridge site to assure themselves of "the reasonableness of the various living accommodations which had been provided, [and] that they actually observe the size and scope of the installations and that some of the complexities of the project be demonstrated to them."[i]
During the war, the Manhattan Project ultimately produced the three bombs used (the Trinity gadget, Little Boy, and Fat Man), as well as an additional unused Fat Man bomb, making the average wartime cost per bomb around $500 million in 1945 dollars. By comparison, the project's total cost by the end of 1945 was about 90% of the total spent on the production of US small arms (not including ammunition) and 34% of the total spent on US tanks during the same period.[336] It was the second most expensive weapons project undertaken by the United States during the war, behind only the Boeing B-29 Superfortress.[343]
Legacy
The political and cultural impacts of the development of nuclear weapons were profound.
The Manhattan Project left a legacy of a network of
The Naval Research Laboratory had long been interested in the prospect of using nuclear power for warship propulsion, and sought to create its own nuclear project. In May 1946, Nimitz, now
The ability of the new reactors to create radioactive isotopes in previously unheard-of quantities sparked a revolution in nuclear medicine. Starting in mid-1946, Oak Ridge began distributing radioisotopes to hospitals and universities, primarily iodine-131 and phosphorus-32 for cancer diagnosis and treatment. Isotopes were also used in biological, industrial and agricultural research.[356]
Its production sites, operating with new technologies, exotic substances, and under conditions of secrecy and haste, also left a vast legacy of waste and environmental damage. At Hanford, for example, corrosive and radioactive wastes were stored in "hastily fabricated, single-shell, steel-lined, underground storage tanks" that were intended to be temporary, awaiting a more permanent solution.[357] Instead, they were neglected and eventually leaked. Issues of this kind resulted in Hanford becoming "one of the most contaminated nuclear waste sites in North America", and the subject of significant cleanup efforts after it was deactivated in the late Cold War.[358]
On handing over control to the Atomic Energy Commission, Groves bid farewell to the people who had worked on the Manhattan Project:
Five years ago, the idea of Atomic Power was only a dream. You have made that dream a reality. You have seized upon the most nebulous of ideas and translated them into actualities. You have built cities where none were known before. You have constructed industrial plants of a magnitude and to a precision heretofore deemed impossible. You built the weapon which ended the War and thereby saved countless American lives. With regard to peacetime applications, you have raised the curtain on vistas of a new world.[359]
The Manhattan Project National Historical Park was established on 10 November 2015.[360]
See also
- The Bomb (film) – 2015 American documentary film
- Oppenheimer (film)
- Timeline of nuclear weapons development
Notes
- ^ Specifically at its Berkeley campus; however, as of 1940, the University of California had not yet established a formal distinction between the university as a whole and its flagship campus at Berkeley. The process of transforming the University into a multi-campus university system began in March 1951 and was not complete until 1960.[9]
- ^ The reaction Teller was most concerned with was: 14
7N
+ 14
7N
→ 24
12Mg
+ 4
2He
(alpha particle) + 17.7 MeV.[34] - Trinity test.[37]
- ^ Natural self-sustaining nuclear reactions have occurred in the very distant past.[105]
- ^ The allusion here is to the Italian navigator Christopher Columbus, who reached the Caribbean in 1492.
- ^ The original project goal in 1942 was to acquire approximately 1,700 short tons (1,500 t) of uranium ore. By the time of the dissolution of the Manhattan District, it had acquired about 10,000 short tons (9,100 t) tons of uranium oxides, 72% of which came from the Congolese ores, 14% from the Colorado plateau, and 9% from Canadian ores.[126]
- ^ Much of the mined ore from the Shinkolobwe mine had a uranium oxide content as high as 65% to 75%, which was many times higher than any other global sources.[129] By comparison, the Canadian ores could be as high as 30%, and American sources, many of them byproducts of the mining of other minerals (especially vanadium), contained less than 1% uranium.[130]
- Arthur Ryder, who translated the line as: "Death am I, and my present task / Destruction." A more common translation has the identification not as "Death," but as "Time." In the passage, the Hindu god Krishna is revealing himself and his true form to Prince Arjuna, imploring Arjuna to fulfill his duty and take part in a war, and assuring him that the fate of those killed is really up to Krishna, not mortal men.[238]
- ^ The seven Congressmen officially informed were: Alben W. Barkley (Senate Majority Leader), Styles Bridges (Ranking minority member of the Sub-Committee on Military Appropriations), Joseph W. Martin Jr. (House Minority Leader), John W. McCormack (House Majority Leader), Sam Rayburn (Speaker of the House), Elmer Thomas (Chair of the Sub-Committee on Military Appropriations), and Wallace H. White (Senate Minority Leader). The five allowed to tour Oak Ridge were: Clarence Cannon, Albert J. Engel, George H. Mahon, J. Buell Snyder, and John Taber.[342]
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- ^ Manhattan District History, Book 7, Volume 1 (Feed Materials and Special Procurement). Vol. Book 7, Volume 1. 1947. pp. 2.14, 5.1, Appendix D.3.. An additional 5% came from "miscellaneous sources", which included some ores recovered by the Alsos Mission from Europe.
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Participant accounts
External links
- "The Atomic Bomb and the End of World War II, A Collection of Primary Sources". George Washington University. Retrieved 27 July 2011.
- "Atomic Heritage Foundation". Atomic Heritage Foundation. Retrieved 27 July 2011.
- "Voices of the Manhattan Project". Atomic Heritage Foundation. Retrieved 10 February 2015. Features hundreds of audio/visual interviews with Manhattan Project veterans.
- "History Center: Los Alamos National Laboratory". Los Alamos National Laboratory. Retrieved 27 July 2011.
- "ORNL: The first 50 Years: History of ORNL". ORNL Review. 25 (3). Archived from the originalon 2 June 2016. Retrieved 13 October 2015.
- Manhattan Project and Allied Scientists Collections at the University of Chicago Special Collections Research Center
- Chadwick, Mark B. (3 December 2021). "Nuclear Science for the Manhattan Project and Comparison to Today's ENDF Data". Nuclear Technology. 207 (sup1): S24–S61. .