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Fat Man - Wikipedia
It was the second of the only two nuclear weapons ever used in warfare, the first being Little Boyand its detonation marked the third nuclear explosion in history. It was built by scientists and engineers at Los Alamos Laboratory using plutonium from the Hanford Essay on atomic bomband it was dropped from the Boeing B Superfortress Bockscar piloted by Major Charles Sweeney. The name Fat Man refers to the early design of the bomb because it had a wide, round shape.
Fat Man was an implosion-type nuclear weapon with a solid plutonium core. The first of that type to be detonated was the Gadget in the Trinity nuclear test less than a month earlier on 16 July at the Alamogordo Bombing and Gunnery Range in New Mexico. Two more were detonated during the Operation Crossroads nuclear tests at Bikini Atoll inand some were produced between andwhen it was superseded by the Mark 4 nuclear bomb.
The Fat Man was retired in Robert Oppenheimer held conferences in Chicago in Juneprior to the Army taking over wartime atomic research, and in Berkeley, Californiain July, at which various engineers and physicists discussed nuclear bomb design issues.
They chose a gun-type design in which two sub-critical masses would be brought together by firing a "bullet" into a "target". Tolman suggested an implosion-type nuclear weaponbut the proposal attracted little interest, essay on atomic bomb. The feasibility of a plutonium bomb was questioned in Wallace Akersthe director of the British " Tube Alloys " project, told James Bryant Conant on 14 November that James Chadwick had "concluded that plutonium might not be a practical fissionable material for weapons because of impurities.
Conant informed Manhattan Project director Brigadier General Leslie R. Groves Jr. The committee concluded that any problems could be overcome simply by requiring higher purity.
Oppenheimer reviewed essay on atomic bomb options in early and gave priority to the gun-type weapon, essay on atomic bomb, [2] but he created the E-5 Group at the Los Alamos Laboratory under Seth Neddermeyer to investigate implosion as a hedge against the threat of pre-detonation.
Implosion-type bombs were determined to be significantly more efficient in terms of explosive yield per unit mass of fissile material in the bomb, because compressed fissile materials react more rapidly and therefore more completely.
Nonetheless, it was decided that the plutonium gun would receive the bulk of the research effort, since it was the project with the least uncertainty involved. It was assumed that the uranium gun-type bomb could be easily adapted from it. The gun-type and implosion-type designs were codenamed " Thin Man " and "Fat Man" respectively, essay on atomic bomb.
These code names were created by Robert Serbera former student of Oppenheimer's who worked on the Manhattan Project. He chose them based on their design shapes; the Thin Man was a very long device, and the name came from the Dashiell Hammett detective novel The Thin Man and series of movies. The Fat Man was round and fat and was named after Sydney Greenstreet 's character in Hammett's The Maltese Falcon.
Little Boy came last as a variation of Thin Essay on atomic bomb. Neddermeyer discarded Serber and Tolman's initial concept of implosion as assembling a series of pieces in favor of one in which a hollow sphere was imploded by an explosive shell.
He was assisted in this work by Essay on atomic bomb BradnerCharles Critchfieldand John Streib. Thompson was brought in as a consultant, and discussed the problem with Neddermeyer in June Thompson was skeptical that an implosion could be made sufficiently symmetric. Oppenheimer arranged for Neddermeyer and Edwin McMillan to visit the National Defense Research Committee 's Explosives Research Laboratory near essay on atomic bomb laboratories of the Bureau of Mines in Bruceton, Pennsylvania a Pittsburgh suburbwhere they spoke to George Kistiakowsky and his team.
But Neddermeyer's efforts in July and August at imploding tubes to produce cylinders tended to produce objects that resembled rocks. Neddermeyer was the only person who believed that implosion was practical, and only his enthusiasm kept the project alive.
Oppenheimer brought John von Neumann to Los Alamos in September to take a fresh look at implosion. After reviewing Neddermeyer's studies, and discussing the matter with Edward Telleressay on atomic bomb, von Neumann suggested the use of high explosives in shaped charges to implode a sphere, which he showed could not only result in a faster assembly of fissile material than was possible with the gun method, but which could greatly reduce the amount of material required, because of the resulting higher density.
Kistiakowsky's name was immediately suggested, and Kistiakowsky was brought into the project as a consultant in October The implosion project remained a backup until Aprilwhen experiments by Emilio G. Segrè and his P-5 Group at Los Alamos on the newly reactor-produced plutonium from the X Graphite Reactor at Oak Ridge and the B Reactor at essay on atomic bomb Hanford site showed that it contained impurities in the form of the isotope plutonium This has a far higher spontaneous fission rate and radioactivity than plutonium The cyclotron -produced isotopes, on which the original measurements had been made, held much lower traces of plutonium Its inclusion in reactor-bred plutonium appeared unavoidable, essay on atomic bomb.
This meant that the spontaneous fission rate of the reactor plutonium was so high that it would be highly likely that it would predetonate and blow itself apart during the initial formation of a critical mass. The only way to use plutonium in a workable bomb was therefore implosion. The impracticability of a gun-type bomb using plutonium was agreed at a meeting in Los Alamos on 17 July All gun-type work in the Manhattan Project was directed at the Little Boy, essay on atomic bomb gun design, and the Los Alamos Laboratory was reorganized, essay on atomic bomb, with almost all of the research focused on the problems of implosion for the Fat Man bomb.
Tuckessay on atomic bomb, and was developed by von Neumann. The 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 believed to be the cause, but it was soon determined that there were multiple allotropes of plutonium. Attention then shifted to the even more malleable δ phase that normally exists in the — °C — °F range.
It was found that this was stable at room temperature when alloyed with aluminum, but aluminum emits neutrons when bombarded with alpha particleswhich would exacerbate the pre-ignition problem.
The metallurgists then hit upon a plutonium—gallium alloywhich stabilized the δ phase and could be hot pressed into the desired spherical shape, essay on atomic bomb. As plutonium was found to essay on atomic bomb readily, the sphere was coated with nickel. The size of the bomb was constrained by the available aircraft, essay on atomic bomb, which were investigated for suitability by Dr. Norman Foster Ramsey. The only Allied aircraft considered capable of carrying the Fat Man without major modification were the British Avro Lancaster and the American Boeing B Superfortress.
Without the availability of the B, dropping the bomb would likely have been impossible. However, this still constrained the bomb to a maximum length of 11 feet 3. Removing the bomb rails allowed a maximum width of 5. Drop tests began in Marchand resulted in modifications to the Silverplate aircraft due to the weight of the bomb, essay on atomic bomb. Various combinations of stabilizer boxes and fins were tested on the Fat Man shape to eliminate its persistent wobble until an arrangement dubbed a "California Parachute", essay on atomic bomb, a cubical open-rear tail box outer surface with eight radial fins inside of it, four angled at 45° and four perpendicular to the line of fall holding the outer square-fin box to the bomb's rear end, was approved.
The early Y model Fat Man was assembled with some 1, bolts. This redesign work was substantial, and only the Y tail design was retained. There were also the Y and Y, which were practice bombs with no detonators at all. It gave a yield of about 20 kilotonnes 84 TJ. The fundamental thing was, of course, very much the same. The bomb was inches 3, essay on atomic bomb. It weighed 10, pounds 4, kg.
The plutonium pit [22] was 3. The depleted uranium tamper was an 8. The plastic shell had a 5-inch mm diameter cylindrical hole running through it, like the hole in a cored apple, in order to allow insertion of the pit as late as possible.
The missing tamper cylinder containing the pit could be slipped in through a hole in the surrounding The explosion symmetrically compressed the plutonium to twice its normal density before the "Urchin" added free neutrons to initiate a fission chain reaction.
The result was the fission of about 1 kilogram 2. The first plutonium core was transported with its polonium-beryllium modulated neutron initiator in the custody of Project Alberta courier Raemer Essay on atomic bomb in a magnesium field carrying case designed for the purpose by Philip Morrison. Magnesium was chosen because it does not act as a tamper.
Three Fat Man high-explosive pre-assemblies designated F31, F32, and F33 were picked up at Kirtland on 28 July by three Bs: Luke the Spook and Laggin' Dragon from the th Composite Group's d Bombardment Squadronand another from the th Army Air Forces Base Unit, essay on atomic bomb. The cores essay on atomic bomb transported to North Field, arriving on 2 August, when F31 was partly disassembled in order to check all its components.
F33 was expended near Tinian during a final rehearsal on 8 August. F32 presumably would have essay on atomic bomb used for a third attack or its rehearsal. On 7 August, the day after the bombing essay on atomic bomb HiroshimaRear Admiral William R.
PurnellCommodore William S. ParsonsTibbets, General Carl Spaatz and Major General Curtis LeMay met on Guam to discuss what should be done next. Parsons said that Project Alberta would have it ready by 11 August, but Tibbets pointed to weather reports indicating poor flying conditions on that day due to a storm and asked if the bomb could be made ready by 9 August. Parsons agreed to try to do so.
Fat Man F31 was assembled on Tinian by Project Alberta personnel, [41] and the physics package was fully assembled and wired. It was placed inside its ellipsoidal aerodynamic bombshell and wheeled out, where it was signed by nearly 60 people, including Purnell, Brigadier General Thomas F. Farrelland Parsons. Bock[46] who flew The Great Artiste with his crew on the mission.
Bockscar was flown by Major Charles W. Sweeney and his crew, essay on atomic bomb, with Commander Frederick L. Ashworth from Project Alberta as the weaponeer in charge of the bomb, essay on atomic bomb. Bockscar lifted off at on the morning of 9 Augustwith Kokura as the primary target and Nagasaki the secondary target.
The weapon was already armed, but with the green electrical safety plugs still engaged. Ashworth changed them to red after ten minutes so that Sweeney could essay on atomic bomb to 17, feet essay on atomic bomb, m in order to get above storm clouds. This fuel would still have to be carried all the way to Japan and back, consuming still more fuel. Replacing the pump would take hours; moving the Fat Man to another aircraft might take just as long and was dangerous as well, as the bomb was live.
Colonel Paul Tibbets and Sweeney therefore elected to have Bockscar continue the mission. The target for the bomb was the city of Kokura, essay on atomic bomb, but it was found to be obscured by clouds and drifting smoke from fires started by a major firebombing raid by Bs on nearby Yahata the previous day.
Three bomb runs were made over the next 50 minutes, burning fuel and repeatedly exposing the aircraft to the heavy defenses of Yahata, but the bombardier was unable to drop visually.
By the time of the third bomb run, Japanese anti-aircraft fire was getting close; Second Lieutenant Jacob Beser was monitoring Japanese communications, and he reported activity on the Japanese fighter direction radio bands.
Hiroshima and Nagasaki Bombings: Were Nuclear Weapons Required to End the War?
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