" Fat Man " is the code name for the atomic bomb that was detonated over the Japanese city of Nagasaki by the United States on August 9, 1945. It is the second of only two nuclear weapons ever used in warfare. , the first being the Little Child, and his explosion marked the third man-made nuclear explosion in history. Built by scientists and engineers at Los Alamos Laboratory using plutonium from Hanford Site and down from Boeing B-29 Superfortress Bockscar . For the Fat Man mission, Bockscar was tested by Major Charles W. Sweeney.
The name Fat Man generally refers to the initial design of the bomb, as it has a wide round shape. It is also known as Mark III. Fat Man is an explosive type nuclear weapon with a solid plutonium core. The first of the kind to be detonated is the Gadget, in the Trinity nuclear test, less than a month earlier on July 16th at the Alamogordo Bomb and the Weapon Area in New Mexico.
Two Fat Man bombs were detonated during a Crossroads nuclear test operation in Bikini Atoll in 1946. About 120 Fat Man units were produced between 1947 and 1949, when they were replaced by the Mark 4 nuclear bomb. The Fat Man was retired in 1950.
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Keputusan awal
In 1942, before the Army took over the atomic wartime research, Robert Oppenheimer held a conference in Chicago in June and Berkeley, California, in July, where various engineers and physicists discussed the issue of nuclear bomb design. A gun-type design is chosen, in which two sub-critical masses will be unified by firing "bullets" into the "target". Richard C. Tolman suggested a blast-type nuclear weapon, but the idea drew a bit of consideration.
The feasibility of plutonium bombs was questioned in 1942. James Conant heard on 14 November from Wallace Akers, the director of the British "Tube Alloys" project, that James Chadwick had "concluded that plutonium might not be a practical material for weapons because of dirt." Conant consulted with Ernest Lawrence and Arthur Compton, who admitted that their scientists at Berkeley and Chicago each knew about the problem, but could not offer a ready solution. Conant told the director of the Manhattan Project, Brigadier General Leslie R. Groves Jr., who then formed a special committee consisting of Lawrence, Compton, Oppenheimer, and McMillan to examine the issue. The committee concluded that any problem can be solved by requiring only higher purity.
Oppenheimer, reviewing his options in early 1943, prioritized weapon-type weapons, but as a hedge against pre-blast threats, he created the E-5 Group at Los Alamos Laboratory under Seth Neddermeyer to investigate the explosion. Implosion-type bombs are determined to be significantly more efficient in terms of explosive results per unit mass of fissile material in bombs, as compressed fissile material reacts faster and is therefore more complete. Nevertheless, it was decided that plutonium weapons would receive most of the research effort, since it was the project with the least amount of uncertainty involved. It is assumed that uranium type bombs can be easily adapted from it.
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Naming
The types of pistols and earthquake-type types are codenamed "Thin Man" and "Fat Man". These code names were created by Robert Serber, a former Oppenheimer student working at the Manhattan Project. He chose them based on their design form; Thin Man will be a very long tool, and the name comes from Dashiell Hammett's detective novel The Thin Man and a series of films of the same name; Fat Man will be round and plump and named after the character of Sydney Greenstreet at The Maltese Falcon . Little Boy will come last, as a variation of Thin Man. The use of the term "boy" for a device of the uranium-235 type of weapon is not known to have any connection with the use of George L. Harrison for the same term on the morning of July 18, 1945, in his report to the President. Harry Truman, when he attended the Potsdam Conference, on the success of the Trinity test two days earlier.
Development
Neddermeyer discards the earliest concepts of all-Serber and Tolman as the assembly of a series of pieces supporting one where the hollow ball is detonated by an explosive shell. He is assisted in this work by Hugh Bradner, Charles Critchfield, and John Streib. L. T. E. Thompson was taken as a consultant, and discussed the problem with Neddermeyer in June 1943. Thompson was skeptical that an explosion could be made quite symmetric. Oppenheimer arranged for Neddermeyer and Edwin McMillan to visit the National Defense Research Explosives Research Laboratory near the Bureau of Mining laboratory in Bruceton, Pennsylvania (a suburb of Pittsburgh), where they talked with George Kistiakowsky and his team. But the efforts of Neddermeyer in July and August on tubes that explode to produce cylinders tend to produce objects that resemble rocks. Neddermeyer is the only person who believes that the explosion is practical, and only his enthusiasm keeps the project alive.
Oppenheimer took John von Neumann to Los Alamos in September 1943 to take a new view of the explosion. After reviewing the Neddermeyer study, and discussing this issue with Edward Teller, von Neumann suggested the use of high explosive charge in the form of a charge to blow the ball, which he showed not only can produce faster fissile assembly than is possible with the pistol method, but which can greatly reducing the amount of material needed, due to the higher density generated. The idea that, under such pressure, the plutonium metal itself would be compressed derived from Teller, whose knowledge of how solid metals behave under heavy pressure is influenced by his pre-war theoretical study of the Earth's core with George Gamow. The prospect of more efficient nuclear weapons impressed Oppenheimer, Teller, and Hans Bethe, but they decided that an explosives expert would be needed. The name Kistiakowsky was immediately suggested, and Kistiakowsky was taken to the project as a consultant in October 1943.
The implosion project remained reserves until April 1944, when experiments by Emilio G. SegrÃÆ'¨ and P-5 Group at Los Alamos on plutonium produced new reactors from the X-10 Graphite Reactor at Oak Ridge and Reactor B on Hanford Site showed that it contained impurities in the form of plutonium-240 isotopes. It has a much higher level of spontaneous fission and radioactivity than plutonium-239. The isotope produced by the cyclotron, in which the original measurements have been made, has a lower plutonium-240 trace. Its inclusion in the reactor generated plutonium appears unavoidable. This means that the spontaneous fission rate of the reactor plutonium is so high that it would be very likely that it would have predetonated and explode itself during the initial formation of the critical mass. The distance required to accelerate plutonium to a speed at which predetonation would tend to require a barrel of a rifle is too long for any existing or planned bombers. The only way to use plutonium in a workable bomb is because of the explosion.
The impracticability of gun-type bombs using plutonium was agreed at a meeting at Los Alamos on July 17, 1944. All types of rifles employed at the Manhattan Project were directed at Little Boy, the design of uranium-enriched weapons, and the Los Alamos Laboratory was reorganized, with almost all research focused on issues explosion for the Fat Man bomb. The idea of ​​using a charge shaped as a three-dimensional explosive lens comes from James L. Tuck, and developed by von Neumann. To overcome the difficulty of aligning some detonations, Luis Alvarez and Lawrence Johnston invented a bursting bridgewire detonator to replace an imprecise primocord detonation system. Robert Christy is credited with performing calculations showing how the dense subcritical plutonium sphere can be compressed into a critical state, greatly simplifying the task, since previous attempts have tried the more difficult compression of hollow spherical shells. After Christy's report, the solid-plutonium core weapon is referred to as "Christy Gadget".
The task of the metallurgists is to determine how to dispose of plutonium into the sphere. The difficulty becomes clear when attempts to measure plutonium density give inconsistent results. At first contamination is believed to be the cause, but it is soon determined that there are several allotropes of plutonium. Fragile? the existing phase at room temperature change to plastic? phase at higher temperatures. Attention then shifted to an even lighter? a phase usually present in the range 300-450 ° C (570-840 ° F). It was found that it is stable at room temperature when mixed with aluminum, but aluminum emits neutrons when bombarded with alpha particles, which will exacerbate pre-ignition problems. Metallurgists then hit a plutonium-gallium alloy, which stabilizes? phase and can be pressed hot to the desired ball shape. When plutonium is found to cause corrosion, the ball is coated with nickel.
The size of the bomb was limited by the available aircraft. The only Allied plane capable of carrying Fat Man is British Avro Lancaster and American Boeing B-29 Superfortress. For logistical and nationalistic reasons, B-29 is preferred, but it is bomb-limited to a maximum length of 11 feet (3.4 m), 5 feet (1.5 m) wide and weighs 20,000 pounds (9,100 kg).. Removing the bomb rails allows a maximum width of 5.5 feet (1.7 m). The fall test began in March 1944, and resulted in modifications to the Silverplate plane due to heavy bombs. High speed photographs reveal that the tail fins are folded under pressure, producing an erratic offspring. Various combinations of stabilizer boxes and fins were tested on the Fat Man form to remove the persistent shake until the setting was dubbed "California Parachute", the outer surface of the open cube box with eight radial fins in it, four tilted at 45 and four perpendicular to the line holding the box square-fin outside to the rear end of the bomb, was approved. In a decline test in the early weeks, Fat Man lost its target with an average of 1,857 feet (566 m), but this was halved in June as bombers became more adept at it.
The initial Y-1222 model of Fat Man is assembled with about 1,500 bolts. This was replaced by the Y-1291 design in December 1944. The redesign work is quite large, and only the Y-1222 tail design is maintained. The next version includes Y-1560, which has 72 detonators; Y-1561, which has 32; and Y-1562, which has 132. There are also Y-1563 and Y-1564, which is a practice bomb without a detonator at all. The last wartime design of Y-1561 was assembled with only 90 bolts.
Due to its intricate firing mechanism and the need for previously untested synchronization of explosives and precision design, it is thought that full testing of the concept is necessary before scientists and military representatives can be confident of doing right in combat conditions. On July 16, 1945, the Y-1561 model, Fat Man, known as Gadgets for security reasons, was detonated in a test explosion at a remote location in New Mexico, known as the "Trinity" test. This gives a yield of about 20 kilotons (84 TJ). Some minor changes were made to the design as a result of the Trinity test. Philip Morrison recalls that "There are some important changes... The underlying stuff, of course, is very similar."
Interior bomb
The bomb has a length of 128 inches (3,300 mm) and a diameter of 60 inches (1,500 mm). It weighs 10,300 pounds (4,700 kg).
Assembly
To allow insertion of a 3.62-inch (92 mm) diameter plutonium hole, containing a 0.8 inches (20 mm) Urlein-modulated neutron initiator, as slowly as possible in a device assembly, 8.75 inches (222 mm) balls. ) the depleted uranium tamper diameter surrounded by 0.125 inches (3.2 mm) thick plastic boron impregnated leather has a 130 cm diameter cylinder hole passing through it, like a hole in a rolled apple. The missing tamper cylinder, which contains a hole, can be tucked through a hole around the navel diameter of 18.5 inches (470 mm). The hole was warm to the touch, emitting 2.4 W/kg-Pu, about 15 W for 6.19 kilograms (13.6 lb) core.
This explosion symmetrically squeezes plutonium into twice the normal density before "Urchin" adds free neutrons to begin a fission chain reaction.
The result is a fission of about 1 kilogram (2.2 pounds) of 6.19 kilograms (13.6 Â £) plutonium in the hole, which is about 16% of the fissile material present. 1 gram (0.035 ° oz) of the bomb material is converted into heat activated energy and radiation, releasing energy equivalent to a 21 kiloton TNT or 88 terajoule detonation.
Nagasaki bombing
The first plutonium core, together with the Urchin-beryllium polonium-beryllium initiator, is transported in Alberta Project courier custody, Raemer Schreiber, in a magnesium-designed field for purposes by Philip Morrison. Magnesium is chosen because it does not act as a tamper. The nucleus departs from Kirtland Army Air Field on a C-54 transport plane from the 320th Composite Group Composite Squadron Carrier Squadron on July 26, and arrives at the North Field at Tinian on July 28. Three pre-blast pre-explosions of Big Fat, designated F31, F32, and F33, were picked up at Kirtland on July 28 by three B-29s; two, Luke the Spook and Laggin 'Dragon, from the 393d Composite Group Bomber Squadron plus one from the AAF Base Unit 216, and transported to North Field, arriving on 2 August. Upon arrival, F31 is partially dismantled to check all its components. F33 was issued near Tinian during the last practice on 8 August, and F31 was the bomb dropped at Nagasaki. F32 may be used for a third attack or training.
In August 1945, Fat Man gathered in Tinian by Project Alberta personnel. When the physics package is fully assembled and connected, it is housed in an aerodynamic udipsoidal and wheeled bomb, where it is signed by nearly 60 people, including Rear Admiral William R. Purnell, Brigadier General Thomas F. Farrell and Captain William S. Parsons. It was then pushed into the bomb bay of the B-29 Superfortress named Bockscar after the assigned pilot, Captain Frederick C. Bock, who flew The Great Artiste with his crew on a mission. Bockscar was flown by Major Charles W. Sweeney and his crew, with Commander Frederick L. Ashworth of Project Alberta as the fighter responsible for the bomb.
Bockscar lifted at 03:47 on the morning of 9th August 1945, with Kokura as the main target and Nagasaki as a secondary target. The weapon is already armed, but with green electrical security plugs still in use. Ashworth turns them into red after ten minutes so Sweeney can climb to 17,000 feet (5,200 m) to get a storm cloud over. During a pre-flight inspection of Bockscar, the flight engineer informed Sweeney that a malfunctioning fuel transfer pump made it impossible to use 640 gallon US (2,400 liters) of fuel carried in a reservoir. This fuel still has to be brought to Japan and back, consuming more fuel. Replacing the pump will take hours; moving Fat Man to another plane may take a long time and also dangerous, because the bomb is alive. The 509 Group Composite Commander Colonel Paul Tibbets and Sweeney therefore chose to have Bockscar continue the mission.
The original target for the bomb was Kokura city, but was found obscured by clouds and the smoke drift from a fire started by a massive bomb attack by 224 B-29 near Yahata the previous day. It covers 70% of the area above Kokura, obscures the purpose. Three bombings were carried out over the next 50 minutes, burning fuel and repeatedly exposing the aircraft to heavy Yawata defenses, but the bomber could not visually drop. At the time of the third bombing, Japan's anti-aircraft shots got closer, and Lieutenant Two Jacob Beser, who monitored Japanese communications, reported activity on Japanese combat-oriented radio bands.
Sweeney then proceeded to an alternate target, Nagasaki. It was also obscured by the cloud, and Ashworth ordered Sweeney to make a radar approach. At the last minute, the bomber, Captain Kermit K. Beahan, found a hole in the cloud. The Fat Man was dropped and, after a free fall for 43 seconds, it exploded at 11:02 local time, at an altitude of about 1,650 feet (500 m). Due to poor visibility due to cloud cover, the bomb lost its detonation point by nearly two miles, and the damage was somewhat less extensive than in Hiroshima.
An estimated 35,000-40,000 people died instantly due to the bombing in Nagasaki. A total of 60,000-80,000 deaths were generated, including from long-term health effects, the strongest being leukemia, with an attribute risk of 46% for bomb victims. The others died later due to related explosions and burns, and hundreds more from radiation sickness due to exposure to early bomb radiation. Most of the direct deaths and injuries he suffered from the bombing were ammunition or industrial workers. Mitsubishi industrial production in the city was also cut off by the attack; the shipyard will produce 80 percent of its full capacity in three to four months, steelwork will take a year to return to substantial production, the electrical work will restart some production within two months and has returned on capacity in six months, and factory recovery weapons up to 60 to 70 percent of the original capacity will take 15 months. The Mitsubishi-Urakami Ordnance Works, the factory that produced the type 91 torpedo that was released in an attack on Pearl Harbor, was destroyed in the explosion.
Postwar development
After the war, two Fat Man Y-1561 bombs were used in a nuclear test "Crossroads" operation in the Pacific Bikini Atoll. The first, known as Gilda after the character Rita Hayworth in the 1946 movie of the same name, was dropped by B-29 Dave's Dream . The bomb lost its destination point with 710 yards (650 m). The second bomb, dubbed Helen of Bikini , was placed, without the assembly of its tail fin, in a steel caisson made of submarine convoy towers, and detonated 90 feet (27 m) below the landing craft of an NGO -60 . Two weapons produce about 23 kilotons (96 TJ) each.
The Los Alamos Laboratory and the Army Air Force have begun work on improving the design. B-45 Tornado, Convair XB-46, Martin XB-48, and Boeing B-47 Stratojet North American bomber, then on the drawing board, have bay-sized bombs to carry the Grand Slam, which is longer but not as wide as a Fat Man. The only American bomber who can carry Fat Man is B-29 and Convair B-36. In November 1945, the Army Air Force requested Los Alamos for 200 Fat Man bombs. At that time there were only two sets of plutonium nuclei and highly explosive assemblies. Air Force Air Force wants improvements on design to make it easier to create, assemble, handle, transport, and store inventory. The W-47 wartime project was resumed, and the fall test continued in January 1946.
The Mark III Mod 0 Fat Man was ordered to be put into production in mid-1946. The high explosives were produced by the Salt Wells Pilot Plant, established by the Manhattan Project as part of Project Camel. A new plant was established at the Iowa Army Ordnance Plant. Mechanical components made or purchased by Rock Island Arsenal. Electrical and mechanical components for about 50 bombs were stockpiled at Kirtland Army Air Field in August 1946, but only nine plutonium cores were available. Production Mod 0 ended in December 1948, when there were still only 53 cores available. Replaced by an upgraded version, known as Mods 1 and 2, which contain a number of small changes, the most important thing is that they do not charge the X-Unit burner system capacitors until they are released from the aircraft. Mod 0 was withdrawn from service between March and July 1949, and in October they have all been rebuilt as Mod 1 and 2. About 120 units of Mark Fat Man III added to the stockpile between 1947 and 1949, when it was replaced by Mark 4 nuclear bomb. Mark III Fat Man has retired in 1950.
Due to the limitations of Mark III Fat Man, the nuclear strike would be a formidable effort in the 1940s after the war. The lead-acid battery that drives the fuzing system remains charged for only 36 hours, after which they need to be refilled. To do this means bomb disassembly, and charging takes 72 hours. Batteries must be removed in any case after nine days or they are rusted. The core of plutonium can not be left for longer, because the heat is damaging the high explosive. Changing the core also requires a bomb to be completely dismantled and reassembled. It takes around 40 to 50 people and takes between 56 and 72 hours, depending on the skills of the bomb assembly team, and in June 1948, the Armed Forces Special Arms Project only had three teams. The only plane capable of carrying the bomb was Silverplate B-29, and the only group equipped with them was the 509th Bomb Group at the Walker Air Force Base in Roswell, New Mexico. First they had to fly to Sandia Base to collect the bombs, and then to the base abroad from which a strike could be installed.
Source of the article : Wikipedia
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