Wednesday, July 30, 2014

Fat Man and Little Boy

Screen reader users, click here to turn off Google Instant. It seems somehow appropriate because of the brinkmanship of Putin to begin to think about what happened the last time this kind of brinkmanship was in full swing.

This morning my wife and I were talking about this and I opened up my Ipad to see the names of the two bombs dropped on Hiroshima and Nagasaki. Little boy was dropped first on Hiroshima and Fat man was dropped on Nagasaki. I remember dying as a boy in Nagasaki before I reincarnated and was reborn in Seattle, Washington. My wife read me a piece from an article online about a GI from the U.S. who married a (I believe it was a Hiroshima girl). He said he was sorry we ever dropped the bomb on Hiroshima. She said it was important that we did because the Japanese Army had told the people the only honorable death was to die fighting or to commit suicide. By dropping the bombs on Hiroshima and Nagasaki she said they saved all the lives of the Japanese people because otherwise they all would have either committed suicide or have died fighting the Americans and British.

  1. Fat Man and Little Boy - Wikipedia, the free encyclopedia

    en.wikipedia.org/wiki/Fat_Man_and_Little_Boy
    Wikipedia
    Fat Man and Little Boy (a.k.a. Shadow Makers in the UK) is a 1989 film that reenacts the Manhattan Project, the secret Allied endeavor to develop the first ...
    ‎Plot - ‎Cast - ‎Basis - ‎Production

  2. Fat Man - Wikipedia, the free encyclopedia

    en.wikipedia.org/wiki/Fat_Man
    Wikipedia
    It was the second of only two nuclear weapons ever used in warfare, the first being Little Boy, and its detonation caused the third man-made nuclear explosion.
    ‎Mark 4 nuclear bomb - ‎Charles Sweeney - ‎Frederick C. Bock - ‎Little boy

  3. Little Boy - Wikipedia, the free encyclopedia

    en.wikipedia.org/wiki/Little_Boy
    Wikipedia
    The names for all three atomic bomb design projects during World War II, Fat Man, Thin Man, and Little Boy, were created by Robert Serber, a former student of ...

  4. Fat Man and Little Boy (1989) - IMDb

    www.imdb.com/title/tt0097336/
    Internet Movie Database
    Rating: 6.5/10 - ‎4,737 votes
    Still of Bonnie Bedelia and Dwight Schultz in Fat Man and Little Boy (1989) Still of Paul Newman in Fat Man and Little Boy (1989) Still of Natasha Richardson in ...

  5. Fat Man and Little Boy (6/9) Movie CLIP - I'm Dead (1989 ...

    www.youtube.com/watch?v=AQ0P7R9CfCY
    Mar 3, 2012 - Uploaded by MOVIECLIPS
    Fat Man and Little Boy Movie Clip - watch all clips http://j.mp/z3v7VS click to subscribe http://j.mp/sNDUs5 ...

    Fat Man

    From Wikipedia, the free encyclopedia
    This article is about the World War II nuclear weapon. For other uses, see Fat Man (disambiguation).
    Fat Man
    Replica of the original "Fat Man" bomb
    Replica of the original "Fat Man" bomb
    Type Nuclear weapon
    Place of origin United States of America
    Production history
    Designer Los Alamos Laboratory
    Produced 1945–1949
    Number built 120
    Specifications
    Weight 10,300 pounds (4,670 kg)
    Length 128 inches (3.3 m)
    Diameter 60 inches (1.5 m)
    Filling Plutonium
    Filling weight 6.2 kilograms (14 lb)
    Blast yield 21 kt (88 TJ)
    "Fat Man" was the codename for the type of atomic bomb that was detonated over the Japanese city of Nagasaki by the United States on 9 August 1945. It was the second of only two nuclear weapons ever used in warfare, the first being Little Boy, and its detonation caused the third man-made nuclear explosion. It was dropped from the Boeing B-29 Superfortress Bockscar, named after its pilot, Captain Frederick C. Bock. For the Fat Man mission, Bockscar was piloted by Major Charles W. Sweeney.
    The name Fat Man refers generically to the early design of the bomb, which was also known as the Mark III. Fat Man was an implosion-type nuclear weapon with a plutonium core. The first 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. This bomb was identical in most respects to the Fat Man used at Nagasaki.
    Two more Fat Man bombs were detonated during the Operation "Crossroads" nuclear tests at Bikini Atoll in 1946. Some 120 Fat Man units were produced between 1947 and 1949, when it was superseded by the Mark 4 nuclear bomb. The Fat Man was retired in 1950.

    Early decisions

    In 1942, prior to the Army taking over wartime atomic research, Robert Oppenheimer held conferences in Chicago in June and Berkeley, California, in July, at which various engineers and physicists discussed nuclear bomb design issues. A gun-type design was chosen, in which two sub-critical masses would be brought together by firing a "bullet" into a "target".[1] The idea of an implosion-type nuclear weapon was suggested by Richard Tolman but attracted scant consideration.[2]
    The feasibility of a plutonium bomb 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 fissionable material for weapons because of impurities."[3] Conant consulted Ernest Lawrence and Arthur Compton, who acknowledged that their scientists at Berkeley and Chicago respectively knew about the problem, but could offer no ready solution. Conant informed the director of the Manhattan Project, Brigadier General Leslie R. Groves, Jr., who in turn assembled a special committee consisting of Lawrence, Compton, Oppenheimer and McMillan to examine the issue. The committee concluded that any problems could be overcome simply by requiring higher purity.[4]
    Oppenheimer, reviewing his options in early 1943, gave priority to the gun-type weapon,[2] but as a hedge against the threat of pre-detonation, he created the E-5 Group at the Los Alamos Laboratory under Seth Neddermeyer to investigate implosion. 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 amount of uncertainty involved. It was assumed that the uranium gun-type bomb could be easily adapted from it.[5]
    The gun-type and implosion-type designs were codenamed "Thin Man" and "Fat Man" respectively. These code names were created by Robert Serber, a former student of Oppenheimer's who worked on the Manhattan Project. He chose them based on their design shapes; the Thin Man would be a very long device, and the name came from the Dashiell Hammett detective novel The Thin Man and series of movies by the same name; the Fat Man would be round and fat and was named after Sydney Greenstreet's character in The Maltese Falcon. Little Boy would come last and was named after Elisha Cook, Jr.'s character in the same film, as referred to by Humphrey Bogart.[6]

    Development

    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 Hugh Bradner, Charles Critchfield and John Streib. L.T.E. Thompson was brought in as a consultant, and discussed the problem with Neddermeyer in June 1943. 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 the laboratories of the Bureau of Mines in Bruceton, Pennsylvania (a Pittsburgh suburb), where 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.[7]
    Fat Man Replica
    Replica displayed in the Wright-Patterson Air Force Museum, beside the Bockscar B-29 that dropped the original device.
    Oppenheimer brought John von Neumann to Los Alamos in September 1943 to look at implosion with a fresh set of eyes. After reviewing Neddermeyer's studies, and discussing the matter with Edward Teller, 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.[8] The idea that, under such pressures, the plutonium metal itself would be compressed came from Teller, whose knowledge of how dense metals behaved under heavy pressure was influenced by his pre-war theoretical studies of the Earth's core with George Gamow.[9] The prospect of more-efficient nuclear weapons impressed Oppenheimer, Teller and Hans Bethe, but they decided that an expert on explosives would be required. Kistiakowsky's name was immediately suggested, and Kistiakowsky was brought into the project as a consultant in October 1943.[8]
    The implosion project remained a backup until April 1944, when experiments by Emilio G. Segrè and his P-5 Group at Los Alamos on the newly reactor-produced plutonium from the X-10 Graphite Reactor at Oak Ridge and the B Reactor at the Hanford site showed that it contained impurities in the form of the isotope plutonium-240. This has a far-higher spontaneous fission rate and radioactivity than plutonium-239. The cyclotron-produced isotopes, on which the original measurements had been made, held much lower traces of plutonium-240. Its inclusion in reactor-bred plutonium appeared unavoidable. 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.[10] The distance required to accelerate the plutonium to speeds where predetonation would be less likely would need a gun barrel too long for any existing or planned bomber. The only way to use plutonium in a workable bomb was therefore implosion.[11]
    Flash X-Ray images of the converging shock waves formed during a test of the high-explosive lens system.
    The impracticability of a gun-type bomb using plutonium was agreed at a meeting in Los Alamos on 17 July 1944. All gun-type work in the Manhattan Project was directed at the Little Boy, enriched-uranium gun design, and the Los Alamos Laboratory was re-re-organized, with almost all of the research oriented around the problems of implosion for the Fat Man bomb.[11] The idea of using shaped charges as three-dimensional explosive lenses came from James L. Tuck, and was developed by von Neumann.[12] To overcome the difficulty of synchronizing multiple detonations, Luis Alvarez came up with the idea of replacing the primacord detonators with exploding-bridgewire detonators.[12] Robert Christy is credited with doing the calculations that showed how a solid subcritical sphere of plutonium could be compressed to a critical state, greatly simplifying the task, since earlier efforts had attempted the more-difficult compression of a hollow spherical shell.[13] After Christy's report, the solid-plutonium core weapon was referred to as the "Christy Gadget".[14]
    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.[15] 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 300–450 °C (570–840 °F) 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.[16]
    Fat Man test unit being raised from the pit into the bomb bay of a B-29 for bombing practice during the weeks before the attack on Nagasaki.
    The size of the bomb was constrained by the available aircraft. The only allied aircraft capable of carrying the Fat Man were the British Avro Lancaster and the American Boeing B-29 Superfortress. For logistic and nationalistic reasons, the B-29 was preferred, but this constrained the bomb to a maximum length of 132 inches (3,400 mm), width of 60 inches (1,500 mm) and weight of 20,000 pounds (9,100 kg). Removing the bomb rails allowed a maximum width of 66 inches (1,700 mm).[17] Drop tests began in March 1944, and resulted in modifications to the Silverplate aircraft due to the weight of the bomb.[18] High-speed photographs revealed that the tail fins folded under the pressure, resulting in an erratic descent. 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", a cubical tail box with fins angled at 45° to the line of fall, was approved.[19] In drop tests in early weeks, the Fat Man missed its target by an average of 1,857 feet (566 m), but this was halved by June as the bombardiers became more proficient with it.[20]
    The early Y-1222 model Fat Man was assembled with some 1,500 bolts.[21][22] This was superseded by the Y-1291 design in December 1944. This redesign work was substantial, and only the Y-1222 tail design was retained.[22] Later versions included the Y-1560, which had 72 detonators; the Y-1561, which had 32; and the Y-1562, which had 132. There was also the Y-1563 and Y-1564, which were practice bombs with no detonators at all.[23] The final wartime Y-1561 design was assembled with just 90 bolts.[21]
    Because of its complicated firing mechanism, and the need for previously untested synchronization of explosives and precision design, it was thought that a full test of the concept was needed before the scientists and military representatives could be confident it would perform correctly under combat conditions. On 16 July 1945, a Y-1561 model Fat Man known as the gadget for security reasons was detonated in a test explosion at a remote site in New Mexico, known as the "Trinity" test. It gave a yield of about 20 kilotonnes (84 TJ).[24] Some minor changes were made to the design as a result of the Trinity test.[25] Philip Morrison recalled that "There were some changes of importance... The fundamental thing was, of course, very much the same."[26]

    Bomb interior

    The bomb was 128 inches (3,300 mm) long and 60 inches (1,500 mm) in diameter. It weighed 10,300 pounds (4,700 kg).[27]
    Fat Man external schematic
    1. One of four AN 219 contact fuzes.
    2. Archie radar antenna.
    3. Plate with batteries (to detonate charge surrounding nuclear components).
    4. X-Unit, a firing set placed near the charge.
    5. Hinge fixing the two ellipsoidal parts of the bomb.
    6. Physics package (see details below).
    7. Plate with instruments (radars, baroswitches and timers).
    8. Barotube collector.
    9. California Parachute tail assembly (0.20-inch (5.1 mm) aluminium sheet).
    Fat Man internal schematic

    Assembly

    Fat Man's detonation method
    Fat Man's nuclear device about to be encased
    Fat Man on its transport carriage
    To allow insertion of the 3.62-inch (92 mm) diameter plutonium pit,[21] containing the 0.8-inch (20 mm) diameter "urchin" modulated neutron initiator, as late as possible in the device's assembly, the spherical 8.75-inch (222 mm) diameter depleted uranium tamper surrounded by a 0.125-inch (3.2 mm) thick shell of boron impregnated plastic had a 5-inch (130 mm) diameter cylindrical hole running through it, like the hole in a cored apple. The missing tamper cylinder, containing the pit, could be slipped in through a hole in the surrounding 18.5-inch (470 mm) diameter aluminium pusher.[28] The pit was warm to touch, emitting 2.4 W/kg-Pu, about 15 W for the 6.19 kilograms (13.6 lb) core.[29]
    The plutonium was compressed to twice its normal density before the "urchin" added free neutrons to initiate a fission chain reaction.[30]
    The result was the fission of about 1 kilogram (2.2 lb) of the 6.19 kilograms (13.6 lb) of plutonium in the pit, i.e. of about 17% of the fissile material present. 1 gram (0.035 oz) of matter in the bomb is converted into the active energy of heat and radiation, releasing the energy equivalent to the detonation of 21 kilotons of TNT or 88 terajoules.[36]

    Bombing of Nagasaki

    Main article: Bombing of Nagasaki
    Mushroom cloud after Fat Man exploded over Nagasaki on 9 August 1945
    The first plutonium core, along with its polonium-beryllium urchin initiator, was transported in the custody of Project Alberta courier Raemer Schreiber in a magnesium-field carrying-case designed for the purpose by Philip Morrison. Magnesium was chosen because it does not act as a tamper.[30] The core departed from Kirtland Army Air Field on a C-54 transport aircraft of the 509th Composite Group's 320th Troop Carrier Squadron on 26 July, and arrived at North Field on Tinian on 28 July. Three Fat Man high-explosive pre-assemblies, designated F31, F32, and F33, were picked up at Kirtland on 28 July by three B-29s; two, Luke the Spook and Laggin' Dragon, from the 509th Composite Group's 393d Bombardment Squadron plus one from the 216th AAF Base Unit, and transported to North Field, arriving on 2 August. Upon arrival, F31 was partly disassembled in order to check all its components. F33 was expended near Tinian during a final rehearsal on 8 August, and F31 was the bomb dropped on Nagasaki. F32 presumably would have been used for a third attack or its rehearsal.[37]
    In August 1945, the Fat Man was assembled on Tinian by Project Alberta personnel. When 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 Rear Admiral William R. Purnell, Brigadier General Thomas F. Farrell and Captain William S. Parsons.[38] It was then wheeled to the bomb bay of the B-29 Superfortress named Bockscar after its normally assigned command pilot, Captain Frederick C. Bock,[39] who flew The Great Artiste with his crew on the mission. Bockscar was flown by Major Charles W. Sweeney and his crew, with Commander Frederick L. Ashworth from Project Alberta as the weaponeer in charge of the bomb.[40]
    Bockscar lifted off at 03:47 on the morning of 9 August 1945, with Kokura as the primary target and Nagasaki the secondary target. The weapon already armed, but with the green electrical safety plugs still engaged. Ashworth changed them to red after ten minutes so that Sweeney could climb to 17,000 feet (5,200 m) in order to get above storm clouds.[41] During pre-flight inspection of Bockscar, the flight engineer notified Sweeney that an inoperative fuel transfer pump made it impossible to use 640 US gallons (2,400 l) of fuel carried in a reserve tank. 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. 509th Composite Group Commander Colonel Paul Tibbets and Sweeney therefore elected to have Bockscar continue the mission.[42]
    Effects of the Fat Man's detonation on Nagasaki
    The original target for the bomb was the city of Kokura, but it was found to be obscured by clouds and drifting smoke from fires started by a major firebombing raid by 224 B-29s on nearby Yawata the previous day. This covered 70% of the area over Kokura, obscuring the aiming point. Three bomb runs were made over the next 50 minutes, burning fuel and exposing the aircraft repeatedly to the heavy defenses of Yawata, but the bombardier was unable to drop visually. By the time of the third bomb run, Japanese antiaircraft fire was getting close, and Second Lieutenant Jacob Beser, who was monitoring Japanese communications, reported activity on the Japanese fighter direction radio bands.[43]
    Sweeney then proceeded to the alternative target, Nagasaki. It too was obscured by cloud, and Ashworth ordered Sweeney to make a radar approach. At the last minute, the bombardier,[41] Captain Kermit K. Beahan,[40] found a hole in the clouds. The Fat Man was dropped, and following a 43-second duration free fall, exploded at 11:02 local time, at an altitude of about 1,650 feet (500 m).[41] The Mitsubishi-Urakami Ordnance Works, the factory that manufactured the type 91 torpedoes released in the attack on Pearl Harbor, was destroyed in the blast. Because of poor visibility due to cloud cover, the bomb missed its intended detonation point by almost two miles, and damage was somewhat less extensive than that in Hiroshima. An estimated 40,000 people were killed outright by the bombing at Nagasaki. Thousands more died later from related blast and burn injuries, and hundreds more from radiation illnesses from exposure to the bomb's initial radiation.[44]

    Post-war development

    Espionage information procured by Klaus Fuchs and Theodore Hall, and to a lesser extent by David Greenglass, led to the first Soviet device, "RDS–1" (above) closely resembling Fat Man, even in its external shape.
    After the war, two Y-1561 Fat Man bombs were used in the Operation "Crossroads" nuclear tests at Bikini Atoll in the Pacific. The first, known as Gilda after Rita Hayworth's character in the 1946 movie of the same name, was dropped by the B-29 Dave's Dream. The bomb missed its aim point by 710 yards (649 m). The second bomb, nicknamed Helen of Bikini, was placed, without its tail fin assembly, in a steel caisson made from a submarine's conning tower, and detonated 90 feet (27 m) beneath the landing craft LSM-60. The two weapons yielded about 23 kilotonnes (96 TJ) each.[45]
    The Los Alamos Laboratory and the Army Air Forces had already commenced work on improving the design. The North American B-45 Tornado, Convair XB-46, Martin XB-48 and Boeing B-47 Stratojet bombers, then on the drawing boards, had bomb bays sized to carry the Grand Slam, which was much longer but not as wide as the Fat Man. The only bombers that could carry the Fat man were the B-29 and the Convair B-36. In November 1945, the Army Air Forces asked Los Alamos for 200 Fat Man bombs. At the time there were only two sets of plutonium cores and high explosive assemblies. The Army Air Forces wanted improvements to the design to make it easier to manufacture, assemble, handle, transport and stockpile. The wartime Project W-47 was continued, and drop tests resumed in January 1946.[46]
    The Mark III Mod 0 Fat Man was ordered to be put into production in mid-1946. High explosives were manufactured by the Salt Wells Pilot Plant, which had been established by the Manhattan Project as part of Project Camel. A new plant was established at the Iowa Army Ordnance Plant. Mechanical components were made or procured by the Rock Island Arsenal. Electrical and mechanical components for about 50 bombs were stockpiled at Kirtland Army Air Field by August 1946, but only nine plutonium cores were available. Production of the Mod 0 ended in December 1948, by which time there were still only 53 cores available. It was replaced by improved versions, known as Mods 1 and 2, which contained a number of minor changes, the most important of which was that they did not charge the X-Unit firing system's capacitors until released from the aircraft. The Mod 0s were withdrawn from service between March and July 1949, and by October they had all been rebuilt as Mods 1 and 2.[47] Some 120 Mark III Fat Man units were added to the stockpile between 1947 and 1949,[48] when it was superseded by the Mark 4 nuclear bomb.[49] The Mark III Fat Man was retired in 1950.[48][50]
    Due to the limitations of the Mark III Fat Man, a nuclear strike would have been a formidable undertaking in the 1940s. The lead-acid batteries that powered the fuzing system remained charged for only 36 hours, after which they needed to be recharged. To do this meant disassembling the bomb, and recharging took 72 hours. The batteries had to be removed in any case after nine days or they corroded. The plutonium core could not be left in for much longer, because its heat damaged the high explosives. Replacing the core also required the bomb to be completely disassembled and reassembled. This required about 40 to 50 men and took between 56 and 72 hours, depending on the skill of the bomb assembly team, and in June 1948 the Armed Forces Special Weapons Project had only three teams. The only aircraft capable of carrying the bomb were Silverplate B-29s, and the only group equipped with them was the 509th Bombardment Group at Walker Air Force Base in Roswell, New Mexico. They would first have to fly to Sandia Base to collect the bombs, and then to an overseas base from which a strike could be mounted.[51]
    As much of the Manhattan Project data leaked by the spies Klaus Fuchs, Theodore Hall and David Greenglass to the Soviet Union concerned Fat Man, the Soviet Union's first nuclear weapon, designated "Joe-1" by the United States, was based closely on Fat Man's design.[52][53] "Joe 1" was detonated on 29 August 1949 as part of Operation "First Lightning".

    Notes

    1. Hoddeson et al. 1993, pp. 42–44.
    2. Hoddeson et al. 1993, p. 55.
    3. Nichols 1987, p. 64.
    4. Nichols 1987, pp. 64–65.
    5. Hoddeson et al. 1993, p. 87.
    6. Serber & Crease 1998, p. 104.
    7. Hoddeson et al. 1993, pp. 86–90.
    8. Hoddeson et al. 1993, pp. 130–133.
    9. Teller 2001, pp. 174–176.
    10. Hoddeson et al. 1993, p. 228.
    11. Hoddeson et al. 1993, pp. 240–244.
    12. Hoddeson et al. 1993, p. 163.
    13. Hoddeson et al. 1993, pp. 270–271.
    14. Hoddeson et al. 1993, pp. 293, 307–308.
    15. Hewlett & Anderson 1962, pp. 244–245.
    16. Baker, Hecker & Harbur 1983, pp. 144–145.
    17. Hansen 1995, pp. 119–120.
    18. Campbell 2005, pp. 8–10.
    19. Hoddeson et al. 1993, pp. 380–383.
    20. Hansen 1995, p. 131.
    21. Coster-Mullen 2012, p. 52.
    22. Hansen 1995, p. 121.
    23. Hansen 1995, p. 127.
    24. Jones 1985, pp. 465,514–517.
    25. Hoddeson et al. 1993, p. 377.
    26. Coster-Mullen 2012, p. 53.
    27. Hansen 1995, p. 145.
    28. Coster-Mullen 2012, p. 186.
    29. Coster-Mullen 2012, p. 49.
    30. Coster-Mullen 2012, p. 45.
    31. Coster-Mullen 2012, p. 41.
    32. Hansen 1995, pp. 122–123.
    33. Coster-Mullen 2012, p. 48.
    34. Coster-Mullen 2012, p. 57.
    35. Sublette, Carey. Nuclear Weapons Frequently Asked Questions "Section 8.0 The First Nuclear Weapons". Retrieved 29 August 2013.
    36. Malik 1985, p. 25.
    37. Campbell 2005, pp. 38–40.
    38. Coster-Mullen 2012, p. 67.
    39. "Bockscar … The Forgotten Plane That Dropped The Atomic Bomb « A Little Touch Of History". Awesometalks.wordpress.com. Retrieved 31 August 2012.
    40. Campbell 2005, p. 32.
    41. Rhodes 1986, p. 740.
    42. Sweeney, Antonucci & Antonucci 1997, pp. 204–205.
    43. Sweeney, Antonucci & Antonucci 1997, pp. 179, 213–215.
    44. Craven & Cate 1953, pp. 723–725.
    45. Coster-Mullen 2012, pp. 84–85.
    46. Hansen 1995, pp. 137–142.
    47. Hansen 1995, pp. 142–145.
    48. Coster-Mullen 2012, p. 87.
    49. Hansen 1995, p. 143.
    50. Hansen 1995, p. 150.
    51. Hansen 1995, pp. 147–149.
    52. Holloway, David (1993). "Soviet Scientists Speak Out". Bulletin of the Atomic Scientists (Educational foundation for Nuclear Science) 49 (4): 18–19. Retrieved 14 August 2011.
    53. Carey Sublette (3 July 2007). "The Design of Gadget, Fat Man, and "Joe 1" (RDS-1)". Nuclear Weapons FAQ. Retrieved 12 August 2011.

    References

    External links

    Wikimedia Commons has media related to Fat Man.

    This page was last modified on 17 July 2014 at 16:56.
    end quote from:

    Fat Man - Wikipedia, the free encyclopedia

    en.wikipedia.org/wiki/Fat_Man
    Wikipedia
    It was the second of only two nuclear weapons ever used in warfare, the first being Little Boy, and its detonation caused the third man-made nuclear explosion.
    ‎Mark 4 nuclear bomb - ‎Charles Sweeney - ‎Frederick C. Bock - ‎Little boy
     

    Little Boy

    From Wikipedia, the free encyclopedia
    For other uses, see Little boy (disambiguation).
    Little Boy (atomic bomb)
    Little boy.jpg
    A post-war Little Boy model
    Type Nuclear weapon
    Place of origin United States
    Production history
    Designer Los Alamos Laboratory
    Produced 1945
    Number built 32
    Specifications
    Weight 9,700 pounds (4,400 kg)
    Length 10 feet (3.0 m)
    Diameter 28 inches (71 cm)
    Filling Uranium-235
    Filling weight 140 lb (64 kg)
    Blast yield 16 kt (67 TJ)
    Little Boy was the codename for the type of atomic bomb dropped on the Japanese city of Hiroshima on August 6, 1945 by the Boeing B-29 Superfortress Enola Gay, piloted by Colonel Paul W. Tibbets, Jr., commander of the 509th Composite Group of the United States Army Air Forces. It was the first atomic bomb to be used as a weapon. The Hiroshima bombing was the second artificial nuclear explosion in history, after the Trinity test, and the first uranium-based detonation. Approximately 600 to 860 milligrams (9.3 to 13.3 grains) of matter in the bomb was converted into the energy of heat and radiation. It exploded with an energy of 16 kilotons of TNT (67 TJ).
    Little Boy was developed by Lieutenant Commander Francis Birch's group of Captain William S. Parsons's Ordnance (O) Division at the Manhattan Project's Los Alamos Laboratory during World War II. Parsons flew on the Hiroshima mission as weaponeer. The Little Boy was a development of the unsuccessful Thin Man nuclear bomb. Like Thin Man, it was a gun-type fission weapon, but derived its explosive power from the nuclear fission of uranium-235. This was accomplished by shooting a hollow cylinder of uranium over another hollow enriched uranium cylinder by means of a charge of nitrocellulose propellant powder. It contained 64 kg (141 lb) of enriched uranium, of which less than a kilogram underwent nuclear fission. Its components were fabricated at three different plants so that no one would have a copy of the complete design.
    After the war ended, it was not expected that the inefficient Little Boy design would ever again be required, and many plans and diagrams were destroyed, but by mid-1946 the Hanford Site reactors were suffering badly from the Wigner effect, so six Little Boy assemblies were produced at Sandia Base. The Navy Bureau of Ordnance built another 25 Little Boy assemblies in 1947 for use by the nuclear-capable Lockheed P2V Neptune aircraft carrier aircraft. All the Little Boy units were withdrawn from service by the end of January 1951.

    Naming

    The names for all three atomic bomb design projects during World War II, Fat Man, Thin Man, and Little Boy, were created by Robert Serber, a former student of Los Alamos Laboratory director Robert Oppenheimer who worked on the Manhattan Project. According to Serber, he chose them based on their design shapes. The "Thin Man" was a long device, and the name came from the Dashiell Hammett detective novel and series of movies by the same name; the "Fat Man" was round and fat, and was named after Sydney Greenstreet's "Kasper Gutman" character in The Maltese Falcon. Little Boy would come last and was named after Elisha Cook, Jr.'s character in the same film, as referred to by Humphrey Bogart.[1]

    Development

    Main article: Manhattan Project
    Because uranium-235 was known to be fissionable, it was the first approach to bomb development pursued. The vast majority of the work came in the form of the isotope enrichment of the uranium necessary for the weapon, since uranium-235 makes up only 1 part in 140 of natural uranium.[2] Enrichment was performed at Oak Ridge, Tennessee, where the electromagnetic separation plant, known as Y-12, became fully operational in March 1944.[3] The first shipments of highly enriched uranium were sent to the Los Alamos Laboratory in June 1944.[4]
    Most of the uranium necessary for the production of the bomb came from the Shinkolobwe mine and was made available thanks to the foresight of the CEO of the High Katanga Mining Union, Edgar Sengier, who had 1,000 long tons (1,000 t) of uranium ore transported to a New York warehouse in 1939.[5] At least part of the 1,200 long tons (1,200 t) of uranium ore and uranium oxide captured by the Alsos Mission in 1944 and 1945 was used in the bomb.[6]
    As part of Project Alberta, Commander A. Francis Birch (left) assembles the bomb while physicist Norman Ramsey watches. This is one of the rare photos where the inside of the bomb can be seen.
    The design was a development of the original Thin Man, a gun-type fission weapon 17 feet (5.2 m) long. Like the Fat Man, it was designed for plutonium but would have worked with enriched uranium as well. The Thin Man design was abandoned after experiments by Emilio G. Segrè and his P-5 Group at Los Alamos on the newly reactor-produced plutonium from Oak Ridge and the Hanford site showed that it contained impurities in the form of the isotope plutonium-240. This has a far higher spontaneous fission rate and radioactivity than the cyclotron-produced plutonium on which the original measurements had been made, and its inclusion in reactor-bred plutonium appeared unavoidable. This meant that the background fission rate of the plutonium was so high that it would be highly likely the plutonium would predetonate and blow itself apart in the initial forming of a critical mass.[7]
    In July 1944, almost all research at Los Alamos was reorganised redirected to the implosion-type plutonium weapon. Overall, responsibility for the uranium gun-type weapon was assigned to Captain William S. Parsons's Ordnance (O) Division. All the design, development and technical work at Los Alamos was consolidated under Lieutenant Commander Francis Birch's group.[8]
    In contrast to the plutonium implosion-type nuclear weapon, the uranium gun-type weapon was straightforward if not trivial to design. The concept was pursued so that in case of a failure to develop a plutonium bomb, it would still be possible to use the gun principle. The gun-type design henceforth had to work with enriched uranium only, and this allowed the Thin Man design to be greatly simplified. A high velocity gun was no longer required, and a simpler weapon could be substituted. This greatly shortened the weapon, so that it would fit into a B-29 bomb bay.[9]
    The design specifications were completed in February 1945, and contracts were let to build the components. Three different plants were used so that no one would have a copy of the complete design. The gun and breech were made by the Naval Gun Factory in Washington, D.C.; the target case and some other components were by the Naval Ordnance Plant in Center Line, Michigan; and the tail fairing and mounting brackets by the Expert Tool and Die Company in Detroit, Michigan.[10] The bomb, except for the uranium payload, was ready at the beginning of May 1945.[11] The uranium 235 projectile was completed on June 15, and the target on July 24.[12] The target and bomb pre-assemblies (partly assembled bombs without the fissile components) left Hunters Point Naval Shipyard, California, on July 16 aboard the cruiser USS Indianapolis, arriving July 26.[13] The target inserts followed by air on July 30.[12]
    While testing of the components was conducted,[12] no full test of a gun-type nuclear weapon occurred before the Little Boy was dropped over Hiroshima. The only test explosion of a nuclear weapon concept had been of an implosion-type device employing plutonium as its fissionable material, and took place on July 16, 1945 at the Trinity nuclear test. There were several reasons for not testing a Little Boy type of device. Primarily, there was little uranium-235 as compared with the relatively large amount of plutonium which, it was expected, could be produced by the Hanford Site reactors.[14] Additionally, the weapon design was simple enough that it was only deemed necessary to do laboratory tests with the gun-type assembly. Unlike the implosion design, which required sophisticated coordination of shaped explosive charges, the gun-type design was considered almost certain to work.[15]
    The danger of accidental detonation made safety a concern. Little Boy incorporated basic safety mechanisms, but an accidental detonation could still occur. Tests were conducted to see if a crash could drive the hollow "bullet" onto the "target" cylinder resulting in a massive release of radiation, or possibly nuclear detonation. These showed that this required an impact of 500 times that of gravity, which made it highly unlikely.[16] There was still concern that a crash and a fire could trigger the explosives.[17] If immersed in water, the uranium halves were subject to a neutron moderator effect. While this would not have caused an explosion, it could have created widespread radioactive contamination. For this reason, pilots were advised to crash on land rather than at sea.[16]

    Design

    The "gun" assembly method. When the hollow uranium projectile was driven onto the target cylinder, a nuclear explosion resulted.
    The Little Boy was 120 inches (300 cm) in length, 28 inches (71 cm) in diameter and weighed approximately 9,700 pounds (4,400 kg).[18] The design used the gun method to explosively force a hollow sub-critical mass of uranium-235 and a solid target cylinder together into a super-critical mass, initiating a nuclear chain reaction. This was accomplished by shooting one piece of the uranium onto the other by means of four cylindrical silk bags of nitrocellulose powder. The bomb contained 64 kg (141 lb) of enriched uranium. Most was enriched to 89% but some was only 50% uranium-235, for an average enrichment of 80%.[19] Less than a kilogram of Uranium underwent nuclear fission, and of this mass only 0.6 g (0.021 oz) was transformed into a different type of energy, initially kinetic energy, then heat and radiation.[20]

    Assembly details

    Inside the weapon, the uranium-235 material was divided into two parts, following the gun principle: the "projectile" and the "target". The projectile was a hollow cylinder with 60% of the total mass (38.5 kg (85 lb)). It consisted of a stack of 9 uranium rings, each 6.25-inch (159 mm) in diameter with a 4-inch (100 mm) bore in the center, and a total length of 7 inches (180 mm), pressed together into the front end of a thin-walled projectile 16.25 inches (413 mm) long. Filling in the remainder of the space behind these rings in the projectile was a tungsten carbide disc with a steel back. At ignition, the projectile slug was pushed 42 inches (1,100 mm) along the 72-inch (1,800 mm) long, 6.5-inch (170 mm) smooth-bore gun barrel. The slug "insert" was a 4 inches (100 mm) cylinder, 7 inches (180 mm) in length with a 1 inch (25 mm) axial hole. The slug comprised 40% of the total fissile mass (25.6 kg or 56 lb). The insert was a stack of 6 washer-like uranium discs somewhat thicker than the projectile rings that were slid over a 1 inch (25 mm) rod. This rod then extended forward through the tungsten carbide tamper plug, impact-absorbing anvil, and nose plug backstop eventually protruding out the front of the bomb casing. This entire target assembly was secured at both ends with locknuts.[21][22]
    When the hollow-front projectile reached the target and slid over the target insert, the assembled super-critical mass of uranium would be completely surrounded by a tamper and neutron reflector of tungsten carbide and steel, both materials having a combined mass of 2,300 kg (5,100 lb).[23] Neutron initiators at the base of the projectile were activated by the impact.[24]
    Little Boy Internal Components.png

    Counter-intuitive design

    For the first fifty years after 1945, every published description and drawing of the Little Boy mechanism assumed that a small, solid projectile was fired into the center of a larger target.[25] However, critical mass considerations dictated that in Little Boy the larger, hollow piece would be the projectile. The assembled fissile core had more than two critical masses of uranium 235. This required one of the two pieces to have more than one critical mass. A hole in the center of the larger mass dispersed the mass and increased the surface area, allowing more fission neutrons to escape, thus preventing a premature chain reaction.[26]
    It was also important for the larger piece to have minimal contact with the neutron-reflecting tungsten carbide tamper until detonation, thus only the projectile's back end was in contact with tungsten carbide. The rest of the tungsten carbide surrounded the sub-critical mass target cylinder (called the "insert" by the designers) with air space between it and the insert. This arrangement packs the maximum amount of fissile material into a gun-assembly design.[26]

    Fuse system

    Arming plugs for a Little Boy type atomic bomb on display at the National Air and Space Museum's Steven F. Udvar-Hazy Center.
    The bomb employed a fusing system that was designed to detonate the bomb at the most destructive altitude. Calculations showed that for the largest destructive effect, the bomb should explode at an altitude of 580 metres (1,900 ft). The resultant fuse design was a three-stage interlock system:[27]
    • A timer ensured that the bomb would not explode until at least fifteen seconds after release, one-quarter of the predicted fall time, to ensure safety of the aircraft. The timer was activated when the electrical pull-out plugs connecting it to the airplane pulled loose as the bomb fell, switching it to internal (24V battery) power and starting the timer. At the end of the 15 seconds the radar altimeters were powered up and responsibility was passed to the barometric stage.[27]
    • The purpose of the barometric stage was to delay activating the radar altimeter firing command circuit until near detonation altitude. A thin metallic membrane enclosing a vacuum chamber (a similar design is still used today in old-fashioned wall barometers) was gradually deformed as ambient air pressure increased during descent. The barometric fuse was not considered accurate enough to detonate the bomb at the precise ignition height, because air pressure varies with local conditions. When the bomb reached the design height for this stage (reportedly 2,000 metres, 6,600 ft) the membrane closed a circuit, activating the radar altimeters. The barometric stage was added because of a worry that external radar signals might detonate the bomb too early.[27]
    • Two or more redundant radar altimeters were used to reliably detect final altitude. When the altimeters sensed the correct height, the firing switch closed, igniting the three BuOrd Mk15, Mod 1 Navy gun primers in the breech plug, which set off the charge consisting of four silk powder bags each containing two pounds of WM slotted-tube cordite. This launched the uranium projectile towards the opposite end of the gun barrel at an eventual muzzle velocity of 300 metres per second (980 ft/s). Approximately 10 milliseconds later the chain reaction occurred, lasting less than 1 microsecond. The radar altimeters used were modified U.S. Army Air Corps APS-13 fighter tail warning radars, nicknamed "Archie", to warn a pilot of another plane approaching from behind.[27]

    Rehearsals

    Little Boy in the bomb pit on Tinian island, before being loaded into Enola Gay's bomb bay. A section of the bomb bay door is visible on the top right.
    The Little Boy pre-assemblies were designated L-1, L-2, L-3, L-4, L-5, L-6, L-7 and L-11. L-1, L-2, L-5 and L-6 were expended in test drops. The first drop test was conducted with L-1 on July 23, 1945. It was dropped over the sea near Tinian in order to test the radar altimeter by the B-29 later known as Big Stink, piloted by Colonel Paul W. Tibbets, the commander of the 509th Composite Group. Two more drop tests over the sea were made on July 24 and 25, using the L-2 and L-5 units in order to test all components. Tibbets was the pilot for both missions, but this time the bomber used was the one subsequently known as Jabit. L-6 was used a dress rehearsal on July 29. The B-29 Next Objective, piloted by Major Charles W. Sweeney, flew to Iwo Jima, where emergency procedures for loading the bomb onto a standby aircraft were practiced. This rehearsal was repeated on July 31, but this time L-6 was reloaded onto a different B-29, Enola Gay, piloted by Tibbets, and the bomb was test dropped near Tinian. L-11 was the assembly used for the Hiroshima bomb.[28][29]

    The bombing of Hiroshima

    The mushroom cloud over Hiroshima after the dropping of Little Boy
    Main article: Atomic bombings of Hiroshima and Nagasaki
    Parsons, the Enola Gay's weaponeer, was concerned about the possibility of an accidental detonation if the plane crashed in takeoff, so he decided not to load the four cordite powder bags into the gun breech until the aircraft was in flight. Parsons and his assistant, Second Lieutenant Morris R. Jeppson, made their way into the bomb bay along the narrow catwalk on the port side. Jeppson held a flashlight while Parsons disconnected the primer wires, removed the breech plug, inserted the powder bags, replaced the breech plug, and reconnected the wires. Before climbing to altitude on approach to the target, Jeppson switched the three safety plugs between the electrical connectors of the internal battery and the firing mechanism from green to red. The bomb was then fully armed. Jeppson monitored the bomb's circuits.[30]
    The bomb was dropped at approximately 08:15  (JST) August 6, 1945. After falling for 44.4 seconds, the time and barometric triggers started the firing mechanism. The detonation happened at an altitude of 1,968 ± 50 feet (600 ± 15 m). It was less powerful than the Fat Man, which was dropped on Nagasaki, but the damage and the number of victims at Hiroshima were much higher, as Hiroshima was on flat terrain, while the hypocenter of Nagasaki lay in a small valley. According to figures published in 1945, 66,000 people were killed as a direct result of the Hiroshima blast, and 69,000 were injured to varying degrees.[31]
    The exact measurement of the yield was problematic, since the weapon had never been tested. President Harry S Truman officially announced that the yield was 20 kilotons of TNT (84 TJ). This was based on Parsons's visual assessment that the blast was greater than what he had seen at the Trinity nuclear test. Since that had been estimated at 18 kilotons of TNT (75 TJ), speech writers rounded up to 20 kilotons. Further discussion was then suppressed, for fear of lessening the impact of the bomb on the Japanese. Data had been collected by Luis Alvarez, Harold Agnew and Lawrence H. Johnston on the instrument plane The Great Artiste but this was not used to calculate the yield at the time.[32]
    After hostilities ended, a survey team from the Manhattan Project that included William Penney, Robert Serber and George T. Reynolds was sent to Hiroshima to evaluate the effects of the blast. From evaluating the effects on objects and structures, Penney concluded that the yield was 12 ± 1 kilotons.[33] Later calculations based on charring pointed to a yield of 13 to 14 kilotons.[34] In 1953, Frederick Reines calculated that the yield as 13 kilotons.[32] This figure became the official yield.[35]
    In 1962, scientists at Los Alamos created a mockup of Little Boy known as "Ichiban" in order to answer some of the unanswered questions, but it failed to clear up all the issues. In 1982, Los Alamos created a replica Little Boy from the original drawings and specifications. This was then tested with enriched uranium but in a safe configuration that would not cause a nuclear explosion. A hydraulic lift was used to move the projectile, and experiments were run to assess neutron emission.[36] Based on this and the data from The Great Artiste, the yield was estimated at 16.6 ± 0.3 kilotons.[37] After considering many estimation methods, a 1985 report concluded that the yield was 15 kilotons ± 20%. [38]
    When 1 pound (0.45 kg) of uranium-235 undergoes complete fission, the yield is 8 kilotons. The 16 kiloton yield of the Little Boy bomb was therefore produced by the fission of no more than 2 pounds (0.91 kg) of uranium-235, out of the 141 pounds (64 kg) in the pit. The remaining 139 pounds (63 kg), 98.5% of the total, contributed nothing to the energy yield.[39]

    Physical effects of the bomb

    The General Effects of the Bomb on Hiroshima. Focuses on damage to the munitions manufacturing industry of the city.
    After being selected in April 1945, Hiroshima was spared conventional bombing to serve as a pristine target, where the effects of a nuclear bomb on an undamaged city could be observed.[40] While damage could be studied later, the energy yield of the untested Little Boy design could be determined only at the moment of detonation, using instruments dropped by parachute from a plane flying in formation with the one that dropped the bomb. Radio-transmitted data from these instruments indicated a yield of about 15 kilotons.[35]
    Comparing this yield to the observed damage produced a rule of thumb called the 5 psi lethal area rule. The number of immediate fatalities will approximately equal the number of people inside the area where the shock wave carries an overpressure of 5 psi or greater.[41] At Hiroshima, that area was 3.5 kilometres (2.2 mi) in diameter.[42]
    The damage came from three main effects: blast, fire, and radiation.[43]

    Blast

    The blast from a nuclear bomb is the result of X-ray-heated air (the fireball) sending a shock/pressure wave in all directions, initially at a velocity greater than the speed of sound,[44] analogous to thunder generated by lightning. Knowledge about urban blast destruction is based largely on studies of Little Boy at Hiroshima. Nagasaki buildings suffered similar damage at similar distances, but the Nagasaki bomb detonated 3.2 kilometres (2.0 mi) from the city center over hilly terrain that was partially bare of buildings.[45]
    Frame house in 1953 nuclear test, 5 psi overpressure
    In Hiroshima almost everything within 1.6 kilometres (1.0 mi) of the point directly under the explosion was completely destroyed, except for about 50 heavily reinforced, earthquake-resistant concrete buildings, only the shells of which remained standing. Most were completely gutted, with their windows, doors, sashes, and frames ripped out.[46] The perimeter of severe blast damage approximately followed the 5 psi contour at 1.8 kilometres (1.1 mi).
    Later test explosions of nuclear weapons with houses and other test structures nearby confirmed the 5 psi overpressure threshold. Ordinary urban buildings experiencing it will be crushed, toppled, or gutted by the force of air pressure. The picture at right shows the effects of a nuclear-bomb-generated 5 psi pressure wave on a test structure in Nevada in 1953.[47]
    A major effect of this kind of structural damage was that it created fuel for fires that were started simultaneously throughout the severe destruction region.

    Fire

    The first effect of the explosion was blinding light, accompanied by radiant heat from the fireball. The Hiroshima fireball was 370 metres (1,200 ft) in diameter, with a surface temperature of 6,000 °C (10,830 °F).[48] Near ground zero, everything flammable burst into flame. One famous, anonymous Hiroshima victim, sitting on stone steps 260 metres (850 ft) from the hypocenter, left only a shadow, having absorbed the fireball heat that permanently bleached the surrounding stone.[49] Simultaneous fires were started throughout the blast-damaged area by fireball heat and by overturned stoves and furnaces, electrical shorts, etc. Twenty minutes after the detonation, these fires had merged into a firestorm, pulling in surface air from all directions to feed an inferno which consumed everything flammable.[50]
    Hiroshima blast and fire damage, U.S. Strategic Bombing Survey map
    The Hiroshima firestorm was roughly 3.2 kilometres (2.0 mi) in diameter, corresponding closely to the severe blast damage zone. (See the USSBS[51] map, right.) Blast-damaged buildings provided fuel for the fire. Structural lumber and furniture were splintered and scattered about. Debris-choked roads obstructed fire fighters. Broken gas pipes fueled the fire, and broken water pipes rendered hydrants useless.[50] At Nagasaki, the fires failed to merge into a single firestorm, and the fire-damaged area was only one fourth as great as at Hiroshima, due in part to a southwest wind that pushed the fires away from the city.[52]
    As the map shows, the Hiroshima firestorm jumped natural firebreaks (river channels), as well as prepared firebreaks. The spread of fire stopped only when it reached the edge of the blast-damaged area, encountering less available fuel.[53]
    Accurate casualty figures are impossible to determine, because many victims were cremated by the firestorm, along with all record of their existence. The Manhattan Project report on Hiroshima estimated that 60% of immediate deaths were caused by fire, but with the caveat that "many persons near the center of explosion suffered fatal injuries from more than one of the bomb effects."[54] In particular, many fire victims also received lethal doses of nuclear radiation.

    Radiation

    Local fallout is dust and ash from a bomb crater, contaminated with radioactive fission products. It falls to earth downwind of the crater and can produce, with radiation alone, a lethal area much larger than that from blast and fire. With an air burst, the fission products rise into the stratosphere, where they dissipate and become part of the global environment. Because Little Boy was an air burst 580 metres (1,900 ft) above the ground, there was no bomb crater and no local radioactive fallout.[55]
    However, a burst of intense neutron and gamma radiation came directly from the fireball. Its lethal radius was 1.3 kilometres (0.8 mi),[42] covering about half of the firestorm area. An estimated 30% of immediate fatalities were people who received lethal doses of this direct radiation, but died in the firestorm before their radiation injuries would have become apparent. Over 6,000 people survived the blast and fire, but died of radiation injuries.[54] Among injured survivors, 30% had radiation injuries[56] from which they recovered, but with a lifelong increase in cancer risk.[57] To date, no radiation-related evidence of heritable diseases has been observed among the survivors' children.[58][59][60]

    Conventional weapon equivalent

    See also: Operation Meetinghouse
    Although Little Boy exploded with the energy equivalent of 16,000 tons of TNT, the Strategic Bombing Survey estimated that the same blast and fire effect could have been caused by only 2,100 tons of conventional bombs: "220 B-29s carrying 1,200 tons of incendiary bombs, 400 tons of high-explosive bombs, and 500 tons of anti-personnel fragmentation bombs."[61] Since the target was spread across a two-dimensional plane, the vertical component of a single spherical nuclear explosion was largely wasted. A cluster bomb pattern of smaller explosions would have been a more energy-efficient match to the target.[61]

    Post-war

    When the war ended, it was not expected that the inefficient Little Boy design would ever again be required, and many plans and diagrams were destroyed. However, by mid-1946 the Hanford Site reactors were suffering badly from the Wigner effect. Faced with the prospect of no more plutonium for new cores and no more polonium for the initiators for the cores that had already been produced, Groves ordered that a number of Little Boys be prepared as an interim measure until a cure could be found. No Little Boy assemblies were available, and no comprehensive set of diagrams of the Little Boy could be found, although there were drawings of the various components, and stocks of spare parts.[62][63]
    At Sandia Base, three Army officers, Captains Albert Bethel, Richard Meyer and Bobbie Griffin attempted to re-create the Little Boy. They were supervised by Harlow W. Russ, an expert on Little Boy who served with Project Alberta on Tinian, and was now leader of the Z-11 Group of the Los Alamos Laboratory's Z Division at Sandia. Gradually, they managed to locate the correct drawings and parts, and figured out how they went together. Eventually, they built six Little Boy assemblies. While the casings, barrels and components were tested, no enriched uranium was supplied for the bombs. By early 1947, the problems caused by the Wigner effect was on its way to solution, and the three officers were reassigned.[62][63]
    The Navy Bureau of Ordnance built 25 Little Boy assemblies in 1947 for use by the nuclear-capable Lockheed P2V Neptune aircraft carrier aircraft. Components were produced by the Naval Ordnance Plants in Pocatello, Idaho, and Louisville, Kentucky. Enough fissionable material was available by 1948 to build ten projectiles and targets, although there were only enough initiators for six.[64] All the Little Boy units were withdrawn from service by the end of January 1951.[65]

    Notes

    1. Serber & Crease 1998, p. 104.
    2. Jones 1985, p. 9.
    3. Jones 1985, p. 138.
    4. Jones 1985, p. 143.
    5. Jones 1985, p. 25.
    6. Rhodes 1995, pp. 160–161.
    7. Hoddeson et al. 1993, p. 228.
    8. Hoddeson et al. 1993, pp. 245–249.
    9. Rhodes 1986, p. 541.
    10. Hoddeson et al. 1993, p. 257.
    11. Hoddeson et al. 1993, p. 262.
    12. Hoddeson et al. 1993, p. 265.
    13. Coster-Mullen 2012, p. 30.
    14. Hansen 1995, pp. 111–112.
    15. Hoddeson et al. 1993, p. 293.
    16. Hansen 1995, p. 113.
    17. Hoddeson et al. 1993, p. 333.
    18. Gosling 1999, p. 51.
    19. Coster-Mullen 2012, p. 18.
    20. Glasstone & Dolan 1977, p. 12.
    21. Sublette, Carey. Nuclear Weapons Frequently Asked Questions "Section 8.0 The First Nuclear Weapons". Retrieved August 29, 2013.
    22. Coster-Mullen 2012, pp. 18–19, 27.
    23. Bernstein 2007, p. 133.
    24. Hoddeson et al. 1993, pp. 263–265.
    25. Samuels 2008.
    26. Coster-Mullen 2012, pp. 23–24.
    27. Hansen 1995a, pp. 2–5.
    28. Campbell 2005, pp. 46, 80.
    29. Coster-Mullen 2012, pp. 100–101.
    30. Coster-Mullen 2012, pp. 34–35.
    31. The Manhattan Engineer District (June 29, 1945). "The Atomic Bombings of Hiroshima and Nagasaki". Project Gutenberg Ebook. docstoc.com. p. 3.
    32. Hoddeson et al. 1993, p. 393.
    33. Malik 1985, pp. 18–20.
    34. Malik 1985, p. 21.
    35. Malik 1985, p. 1.
    36. Coster-Mullen 2012, pp. 86–87.
    37. Malik 1985, p. 16.
    38. Malik 1985.
    39. Glasstone & Dolan 1977, pp. 5, 6.
    40. Groves 1962, p. 267, "To enable us to assess accurately the effects of the [nuclear] bomb, the targets should not have been previously damaged by air raids." Four cities were chosen, including Hiroshima and Kyoto. War Secretary Stimson vetoed Kyoto, and Nagasaki was substituted. p. 275, "When our target cities were first selected, an order was sent to the Army Air Force in Guam not to bomb them without special authority from the War Department.".
    41. Glasstone 1962, p. 629.
    42. Glasstone & Dolan 1977, p. Nuclear Bomb Effects Computer.
    43. Glasstone & Dolan 1977, p. 1.
    44. Diacon 1984, p. 18.
    45. Glasstone & Dolan 1977, pp. 300, 301.
    46. The Atomic Bombings of Hiroshima and Nagasaki, 1946, p. 14.
    47. Glasstone & Dolan 1977, p. 179.
    48. Nuclear Weapon Thermal Effects 1998.
    49. Human Shadow Etched in Stone.
    50. Glasstone & Dolan 1977, pp. 300-304.
    51. D'Olier 1946, pp. 22–25.
    52. Glasstone & Dolan 1977, p. 304.
    53. The Atomic Bombings of Hiroshima and Nagasaki, 1946, pp. 21-23.
    54. The Atomic Bombings of Hiroshima and Nagasaki, 1946, p. 21.
    55. Glasstone & Dolan 1977, p. 409 "An air burst, by definition, is one taking place at such a height above the earth that no appreciable quantities of surface material are taken up into the fireball. . . the deposition of early fallout from an air burst will generally not be significant. An air burst, however, may produce some induced radioactive contamination in the general vicinity of ground zero as a result of neutron capture by elements in the soil." p. 36, "at Hiroshima . . . injuries due to fallout were completely absent.".
    56. Glasstone & Dolan 1977, pp. 545, 546.
    57. Richardson RR 2009.
    58. Genetic Effects.
    59. Izumi BJC 2003.
    60. Izumi IJC 2003.
    61. D'Olier 1946, p. 24.
    62. Coster-Mullen 2012, p. 85.
    63. Abrahamson & Carew 2002, pp. 41–42.
    64. Hansen 1995, pp. 116–118.
    65. Hansen 1995, p. 3.

    References

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