Разделение изотопов и применение их в ядерном реакторе

Thin Man

Thin Man casings. A Fat Man casing is also visible in the photo background.

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 as cyclotron plutonium.[135] This made reactor plutonium unsuitable for use in a gun-type weapon. The plutonium-240 would start the chain reaction too quickly, causing a predetonation which would release enough energy to disperse the critical mass with a minimal amount of plutonium reacted (a fizzle). A faster gun was suggested but found to be impractical. The possibility of separating the isotopes was considered and rejected, as plutonium-240 is even harder to separate from plutonium-239 than uranium-235 from uranium-238.[136]

Work on an alternative method of bomb design, known as implosion, had begun earlier at the instigation of the physicist Seth Neddermeyer. Implosion would use chemical explosive lenses to inwardly crush a sub-critical sphere of fissile material into a smaller and denser form. When the fissile atoms were packed closer together, the rate of neutron capture would increase, and the mass would become a critical mass. The metal needed to travel only very short distances, so the critical mass would be assembled in much less time than it would take with the gun method.[137] Neddermeyer's 1943 and early 1944 investigations into implosion showed promise, but also made it clear that the problem would be much more difficult from a theoretical and engineering perspective than the gun design. But by July 1944, having concluded plutonium could not be used in a gun design, Oppenheimer opted for implosion. John von Neumann, who had experience with shaped charges used in armor-piercing shot and shell, argued that not only would implosion reduce the danger of predetonation and fizzle, but would make more efficient use of the fissionable material.[138] In August 1944, Oppenheimer implemented a sweeping reorganization of the Los Alamos laboratory to focus on implosion.[139]

Separation process

 

Meanwhile, the chemists considered the problem of 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 for separating uranium and plutonium, which was chosen for the pilot separation plant. A second separation process using bismuth phosphate was developed by Seaborg and Stanly G. Thomson.[140] By May 1943, Greenewalt preferred the second process, but both processes were eventually used in combination.[141] 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%.[125]

Chemical separation plant at Hanford

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.[142] 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-foot (5.4 m) by 13-foot (4.0 m) by 20-foot (6.1 m) cells.[143] 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, all work in the separation plants had to be conducted by remote control using closed-circuit television. 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.[144] On 5 February 1945, Matthias hand-delivered the first shipment of 80 grams (2.8 oz) of 95%-pure plutonium nitrate to a Los Alamos courier in Los Angeles.[134]

Metallurgy

The ultimate task of the metallurgists was to figure out how to cast plutonium into a hollow sphere. The difficulties became apparent when attempts to measure the density of plutonium gave inconsistent results. At first contamination was believed to be the cause, but it was soon determined that there were multiple allotropes (molecular configurations) of plutonium.[145] The brittle α phase that exists at room temperature changes to the plastic β phase at higher temperatures. Attention then shifted to the even more malleable δ phase that normally exists in the 300 °C to 450 °C range. It was found that this was stable at room temperature when alloyed with aluminum, but aluminum emits neutrons when bombarded with alpha particles, which would exacerbate the pre-ignition problem. The metallurgists then hit upon a plutonium-gallium alloy, which stabilized the δ phase and could be hot pressed into the desired spherical shape. As plutonium was found to corrode readily, the sphere was coated with nickel.[146]

The work proved dangerous. By the end of the war, half the experienced chemists and metallurgists had to be removed from work with plutonium when unacceptably high levels of the element appeared in their urine. 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. The hemispheres for the first plutonium pit were produced and delivered on 2 July 1945. Three more hemispheres followed on 23 July and were delivered three days later.

Implosion weapon design

Main article: Fat Man

An implosion-type nuclear bomb

The accelerated effort on an implosion design, codenamed Fat Man, began in August 1944. The explosives group was headed by George Kistiakowsky.[150] The design of lenses that detonated with just the right shape and velocity turned out to be slow, difficult and frustrating.[151] Various explosives were tested before settling on composition B as the fast explosive and baratol as the slow explosive.[152] Getting the shape just right required fast, reliable and safe electrical detonators. It was therefore decided to use exploding-bridgewire detonators. A contract for their manufacture was given to Raytheon.[153] To study the behavior of converging shock waves, Serber devised the RaLa Experiment, which used the short-lived radioisotope lanthanum-140, a potent source of gamma radiation.[154] A polonium-beryllium modulated neutron initiator was developed to start the chain reaction at precisely the right moment.[155] Testing required up to 500 curies per month of polonium, which fortunately the Monsanto Company was able to deliver.[156]

Trinity

Main article: Trinity (nuclear test)

Because of the complexity of an implosion-style weapon, it was decided that, despite the waste of fissile material, an initial test would be required. Groves approved the test, subject to the active material being recovered. Consideration was therefore given to a controlled fizzle but Oppenheimer soon opted instead for a full-scale explosion inside a containment vessel. This would enable the active material to be recovered in the event of a failure, as Groves did not relish the prospect of explaining the loss of a billion dollars worth of plutonium to a senate committee.[157] Oppenheimer gave the nuclear test the codename "Trinity".[158]

 

The explosives of the Gadget were raised up to the top of the tower for the final assembly

In March 1944, planning for the test was assigned to Kenneth Bainbridge, a professor of physics at Harvard, working under Kistiakowsky. Bainbridge selected the Alamogordo Bombing Range near Alamogordo Army Airfield as the site for the test.[159] Bainbridge worked with Captain Samuel P. Davalos on the construction of the Trinity Base Camp and its facilities, which included barracks, warehouses, workshops, an explosive magazine and a commissary.[160]

The cylindrical containment vessel, codenamed "Jumbo", measuring 25 feet (7.6 m) long and 12 feet (3.7 m) wide, was fabricated at great expense from 214 tons of iron and steel by Babcock & Wilcox in Barberton, Ohio. It was brought in a special railroad car to a siding in Pope, New Mexico, and was transported the last 25 miles (40 km) from there to the test site on a trailer pulled by two tractors. By the time it arrived, confidence in the implosion method was high enough and the availability of plutonium was sufficient enough that Oppenheimer decided not to use it. Instead, it was hoisted up in a steel tower 800 yards (730 m) from the gadget as a rough measure of how powerful the explosion would be. In the end, "Jumbo" survived, though its tower did not, adding credence to the widespread belief that Jumbo would have successfully contained a fizzled explosion.[161][162]

A pre-test explosion was conducted on 7 May 1945 to calibrate the instruments. A wooden test platform was erected 800 yards (730 m) from Ground Zero and piled with 100 tons of TNT spiked with nuclear fission products in the form of a molten irradiated uranium slug from Hanford. This explosion was observed by Oppenheimer and Groves' new deputy commander, Brigadier General Thomas Farrell. The pre-test produced data which proved vital for the Trinity test.

 

For the actual test, the device, nicknamed the gadget, was hoisted to the top of a 100-foot-high steel tower (30 m) for detonation, since this 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. Observers included Bush, Chadwick, Conant, Farrell, Fermi, Groves, Lawrence, Oppenheimer and Tolman. At 05:30 on 16 July 1945 the gadget exploded with an energy equivalent of around 20 kilotons of TNT, leaving a crater of radioactive glass in the desert 250 feet (76 m) wide and 6 feet (1.8 m) deep. 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.

Foreign Intelligence

Main article: Operation Alsos

The Manhattan Project was charged with gathering intelligence on the German nuclear energy project. It was believed that the Japanese atomic program was not far advanced because Japan had little access to uranium ore, but it was initially feared that Germany was very close to developing its own weapons. At the instigation of the Manhattan Project, a bombing and sabotage campaign was carried out against heavy water plants in German-occupied Norway.[167] A small mission was created, jointly staffed by the Office of Naval Intelligence, OSRD, the Manhattan Project and Army Intelligence (G-2), to investigate enemy scientific developments. It was not restricted to those involving nuclear weapons.[168] The Chief of Army Intelligence, Major General George V. Strong, appointed Lieutenant Colonel Boris T. Pash to command the unit,[169] which was codename "Alsos", a Greek word meaning "grove".[170] As head of the Counter Intelligence Branch of the Western Defense Command, Pash had investigated suspected Soviet espionage at the Radiation Laboratory in Berkeley.

The German experimental nuclear reactor at Haigerloch

The Alsos Mission to Italy questioned staff of the physics laboratory at the University of Rome following the capture of the city in June 1944.[172] Meanwhile Pash formed a second Alsos Mission in London under the command of Captain Horace K. Calvert to participate in Operation Overlord. This was to be a combined British and American mission.[173] Groves considered the risk that the Germans might attempt to disrupt the Normandy landings with radioactive poisons was sufficient to warn General Dwight D. Eisenhower and send an officer to brief his chief of staff, Lieutenant General Walter Bedell Smith.[174] Under the codename Operation Peppermint, special equipment was prepared and Chemical Warfare Service teams were trained in its use.[

Following in the wake of the advancing Allied armies, Pash and Calvert interviewed Frédéric Joliot-Curie about the activities of German scientists. They spoke to officials at Union Minière du Haut Katanga about uranium shipments to Germany. They tracked down 68 tons of ore in Belgium and 30 tons in France. The interrogation of German prisoners indicated that uranium and thorium were being processed in Oranienburg, so Groves arranged for it to be bombed on 15 March 1945.[176] An Alsos team went to Stassfurt in the Soviet Occupation Zone and retrieved 11 tons of ore from WIFO.[177] In April 1945, Pash, in command of a composite force known as T-Force, conducted Operation Harborage, a sweep behind enemy lines of the cities of Hechingen, Bisingen and Haigerloch that were the heart of the German nuclear effort. T-Force captured the nuclear laboratories, documents, equipment and supplies, including heavy water and 1.5 tons of metallic uranium.

Alsos teams rounded up German scientists including Kurt Diebner, Otto Hahn, Walther Gerlach, Werner Heisenberg and Carl Friedrich von Weizsäcker, who were taken to England where they were interned at Farm Hall, a bugged house in Godmanchester. Within days after the bombs were detonated in Japan, Heisenberg figured out what the Allies had done, explaining it to several other imprisoned nuclear project physicists (and the hidden microphones).[179]

Bombing of Hiroshima and Nagasaki

Main article: Atomic bombings of Hiroshima and Nagasaki

Preparations

Starting in November 1943, the Army Air Forces Materiel Command at Wright Field, Ohio, began Silverplate, the codename modification of B-29s to carry the bombs. Test drops were carried out at Muroc Army Air Field, California.[180] Groves met with the Chief of United States Army Air Forces (USAAF), General Henry H. Arnold, in March 1944 to discuss the delivery of the finished bombs to their targets.[181] 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 Avro Lancaster, but using a British aircraft would have caused difficulties with maintenance. Groves hoped that the American Boeing B-29 Superfortress could be modified to carry Thin Man by joining its two bomb bays together.[182] Arnold promised that no effort would be spared to modify B-29s to do the job, and designated Major General Oliver P. Echols as the USAAF liaison to the Manhattan Project.[181] President Roosevelt instructed Groves that if the atomic bombs were ready before the war with Germany ended, he should be ready to drop them on Germany.[183]

Silverplate B-29 Straight Flush. Note lack of gun turrets. The tail code of the 444th Bombardment Group is painted on for security reasons.

The 509th Composite Group was activated on 17 December 1944 at Wendover Army Air Field, Utah, under the command of Colonel Paul W. Tibbets. This base, close to the border with Nevada, was codenamed "Kingman" or "W-47". Training was conducted at Wendover and at Batista Army Airfield, Cuba, where the 393d Bombardment Squadron practiced long-distance flights over water. A special unit known as Alberta was formed at Los Alamos under Captain William S. Parsons as part of the Manhattan Project to assist in preparing and delivering the bombs.[184] Commander Frederick L. Ashworth from Alberta met with Fleet Admiral Chester W. Nimitz on Guam in February 1945 to inform him of the project. While he was there, Ashworth selected North Field on Tinian as a base for the 509th Composite Group, and reserved space for the group and its buildings. The group deployed there in July 1945.[185] Farrell arrived at Tinian on 30 July as the Manhattan Project representative.[186]

Most of the components for Little Boy left San Francisco on the cruiser USS Indianapolis on 16 July and arrived on Tinian on 26 July. Four days later the ship was sunk by a Japanese submarine. The remaining components, which included some uranium-235, were delivered by three C-54 Skymasters of the Air Transport Command.[187] Two Fat Man assemblies travelled to Tinian in specially modified 509th Composite Group B-29s. The first plutonium core went in a special C-54.[188] A joint targeting committee of the Manhattan District and USAAF was established to determine which cities in Japan should be targets, and recommended Kokura, Hiroshima, Niigata and Kyoto. At this point, Secretary of War Henry L. 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. Groves therefore asked Arnold to remove Kyoto not just from the list of nuclear targets, but from targets for conventional bombing as well.[189] One of Kyoto's substitutes was Nagasaki.[190]

The use of the bombs

 

In May 1945, an Interim Committee was created to advise and report on wartime and postwar policies regarding the use of nuclear energy. The committee was chaired by Stimson, with James F. Byrnes, a former US Senator soon to be Secretary of State, as President Truman's personal representative; Ralph A. Bard, the Under Secretary of the Navy; William L. Clayton, the Assistant Secretary of State; Vannevar Bush; Karl T. Compton, the Chief of the Office of Field Service in the Office of Scientific Research and Development and president of Massachusetts Institute of Technology; James B. Conant; and George L. Harrison, an assistant to Stimson and president of New York Life Insurance Company. The Interim Committee in turn established a scientific panel consisting of Arthur Compton, Fermi, Lawrence and Oppenheimer to advise it on scientific issues. In its presentation to the Interim Committee, the scientific panel offered its opinion not just on the likely physical effects of an atomic bomb, but on its likely military and political impact.[191]

At the Potsdam Conference in Germany, President Harry S. Truman was told that the Trinity test had been successful. He told Joseph Stalin, the leader of the Soviet Union, that the US had a new superweapon, without giving any details. This was the first communication from the US to the Soviet Union about the bomb, but Stalin already knew about it from Russian espionage agents.[192] The authorization to use the bomb against Japan had been given, and no alternatives were considered after the Japanese rejection of the Potsdam Declaration.[193]

On 6 August 1945, the 393d Bombardment Squadron B-29 Enola Gay, piloted and commanded by Tibbets, lifted off from North Field at 02:45 Tinian time, with Parsons on board as weaponeer, and with the Little Boy weapon in its bomb bay. Hiroshima, an important army depot and port of embarkation, was the primary target of the mission, with Kokura and Nagasaki as alternative targets. With Farrell's permission, Parsons completed the bomb assembly in the air to minimize the risks during takeoff. At 08:09 Tibbets started his bomb run and handed control over to his bombardier, Major Thomas Ferebee. The bomb was released from 31,600 feet (9,600 m) shortly after 09:15 and the aircraft made a 150° bank to maximize the distance between itself and the blast.[194] The bomb detonated at an altitude of 1,750 feet (530 m). The blast was later estimated to be the equivalent of 13 kilotons of TNT (54 TJ).[195] An area approximately 4.7 square miles (12 km2) was destroyed. Japanese officials determined that 69% of Hiroshima's buildings were destroyed and another 6–7% damaged. About 70,000 to 80,000 people, or some 30% of the population of Hiroshima, were killed immediately, and another 70,000 injured.[196]

Fat Man explodes over Nagasaki, Japan, August 9, 1945.

On the morning of 9 August 1945, the B-29 Bockscar, piloted by the 393d Bombardment Squadron's commander, Major Charles W. Sweeney, lifted off with a Fat Man on board. This time, Ashworth served as weaponeer and Kokura was the primary target. Sweeney took off with his weapon already armed but with the electrical safety plugs still engaged. When they reached Kokura, they found cloud cover had obscured the city, prohibiting the visual attack required by orders. After three runs over the city, and with fuel running low because a transfer pump on a reserve tank had failed before take-off, they headed for the secondary target, Nagasaki. Fuel consumption calculations made en route indicated that Bockscar would be forced to divert to Okinawa. Ashworth decided that a radar approach would be used if the target was obscured. A last-minute break in the clouds over Nagasaki allowed Bockscar's bombardier, Captain Kermit Beahan, to visually sight the target as ordered. The Fat Man was dropped from 29,000 feet (8,800 m) over the city's industrial valley midway between the Mitsubishi Steel and Arms Works in the south and the Mitsubishi-Urakami Ordnance Works in the north. The blast was confined to the Urakami Valley and a major portion of the city was protected by the intervening hills. The resulting explosion had a blast yield equivalent to 21 kilotons of TNT (88 TJ), roughly the same as the Trinity blast. About 44% of the city was destroyed; 35,000 people were killed and 60,000 injured.

Groves expected to have another atomic bomb ready for use on 19 August, with three more in September and a further three in October.[199] Two more Fat Man assemblies were readied. When the Japanese initiated surrender negotiations, Groves ordered the shipments suspended. The third core was scheduled to leave Kirtland Field for Tinian on 12 August.[198] Robert Bacher was packaging it at the Ice House at Los Alamos when he received word.[200] On 11 August, Groves phoned Colonel Stafford L. Warren, the head of the Manhattan Project's health and safety program, with orders to organize a survey team to report on the damage and radioactivity at Hiroshima and Nagasaki. 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.[201]

After the war

Presentation of the Army–Navy "E" Award at Los Alamos on 16 October 1945. Standing, left to right: J. Robert Oppenheimer, unidentified, unidentified, Kenneth Nichols, Leslie Groves, Robert Gordon Sproul, William Sterling Parsons

In anticipation of the bombings, Groves had Henry DeWolf Smyth prepare a history for public consumption. Atomic Energy for Military Purposes (better known as the "Smyth Report") was released to the public on 12 August 1945.[202] Groves and Nichols presented Army–Navy "E" Awards to key contractors, whose involvement had hitherto been secret. Over twenty awards of the Presidential Medal for Merit were made to key contractors and scientists, including Bush and Oppenheimer. Military personnel received the Legion of Merit, including the commander of the Women's Army Corps detachment, Captain Arlene G. Scheidenhelm.[203]

Nichols recommended that S-50 and the Alpha tracks at Y-12 be closed down. This was done in September.[204] Although performing better than ever,[205] 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, thereby cutting the Tennessee Eastman payroll from 8,600 to 1,500 and saving $2 million a month.[206]