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161-765: Little Boy is the name of the type of atomic bomb used in the bombing of the Japanese city of Hiroshima on 6 August 1945 during World War II , making it the first nuclear weapon used in warfare. The bomb was dropped from the Boeing B-29 Superfortress Enola Gay piloted by Colonel Paul W. Tibbets Jr. , commander of the 509th Composite Group , and Captain Robert A. Lewis . It exploded with an energy of approximately 15 kilotons of TNT (63  TJ ) and had an explosion radius of approximately 1.3 kilometers which caused widespread death across

322-513: A misnomer , as their energy comes from the nucleus of the atom, just as it does with fusion weapons. In fission weapons, a mass of fissile material ( enriched uranium or plutonium ) is forced into supercriticality —allowing an exponential growth of nuclear chain reactions —either by shooting one piece of sub-critical material into another (the "gun" method) or by compression of a sub-critical sphere or cylinder of fissile material using chemically fueled explosive lenses . The latter approach,

483-399: 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 cordite powder. This was a widely used smokeless propellant consisting of a mixture of 65 percent nitrocellulose , 30 percent nitroglycerine , 3 percent petroleum jelly , and 2 percent carbamite that was extruded into tubular granules. This gave it

644-518: A nuclear explosion . Both bomb types release large quantities of energy from relatively small amounts of matter . The first test of a fission ("atomic") bomb released an amount of energy approximately equal to 20,000 tons of TNT (84  TJ ). The first thermonuclear ("hydrogen") bomb test released energy approximately equal to 10 million tons of TNT (42 PJ). Nuclear bombs have had yields between 10 tons TNT (the W54 ) and 50 megatons for

805-665: A policy of deliberate ambiguity , it does not acknowledge having them. Germany , Italy , Turkey , Belgium , the Netherlands , and Belarus are nuclear weapons sharing states. South Africa is the only country to have independently developed and then renounced and dismantled its nuclear weapons. The Treaty on the Non-Proliferation of Nuclear Weapons aims to reduce the spread of nuclear weapons, but there are different views of its effectiveness. There are two basic types of nuclear weapons: those that derive

966-696: A conference—called for in the manifesto—in Pugwash, Nova Scotia , Eaton's birthplace. This conference was to be the first of the Pugwash Conferences on Science and World Affairs , held in July 1957. By the 1960s, steps were taken to limit both the proliferation of nuclear weapons to other countries and the environmental effects of nuclear testing . The Partial Nuclear Test Ban Treaty (1963) restricted all nuclear testing to underground nuclear testing , to prevent contamination from nuclear fallout, whereas

1127-457: A copy of the complete design. Unlike the implosion design, which required sophisticated coordination of shaped explosive charges, the gun-type design was considered almost certain to work so it was never tested before its first use at Hiroshima. After the war, numerous components for additional Little Boy bombs were built. By 1950, five complete weapons had been created, and these were retired by November 1950. There are two primary accounts of how

1288-417: A crash that could destroy or damage the military base from which the weapon was launched. 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). The design used the gun method to explosively force a hollow sub- critical mass of enriched uranium and a solid target cylinder together into a super-critical mass, initiating

1449-447: A difference of only 0.14 miles (0.23 km). The areas affected for each would be 3.02 square miles (7.8 km) and 3.91 square miles (10.1 km), respectively. As such, the practical differences in effects at these yield ranges are smaller than may at first appear, if one assumes that there is a linear relationship between yield and damage. Although Little Boy exploded with the energy equivalent of around 15 kilotons of TNT, in 1946

1610-458: A faster and less vulnerable attack, the development of long-range intercontinental ballistic missiles (ICBMs) and submarine-launched ballistic missiles (SLBMs) has given some nations the ability to plausibly deliver missiles anywhere on the globe with a high likelihood of success. More advanced systems, such as multiple independently targetable reentry vehicles (MIRVs), can launch multiple warheads at different targets from one missile, reducing

1771-614: A few nations possess such weapons or are suspected of seeking them. The only countries known to have detonated nuclear weapons—and acknowledge possessing them—are (chronologically by date of first test) the United States , the Soviet Union (succeeded as a nuclear power by Russia ), the United Kingdom , France , China , India , Pakistan , and North Korea . Israel is believed to possess nuclear weapons, though, in

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1932-555: A fission bomb to initiate them. Such a device might provide a simpler path to thermonuclear weapons than one that required the development of fission weapons first, and pure fusion weapons would create significantly less nuclear fallout than other thermonuclear weapons because they would not disperse fission products. In 1998, the United States Department of Energy divulged that the United States had, "...made

2093-434: A fuel. All the design, development, and technical work at Los Alamos was consolidated under Lieutenant Commander Francis Birch 's group. In contrast to the plutonium implosion-type nuclear weapon and the plutonium gun-type fission weapon, the uranium gun-type weapon was much simpler to design. As a high-velocity gun was no longer required, the overall length of the gun barrel could be dramatically decreased, and this allowed

2254-497: A full-scale test in the implosion-type design made it much more difficult to establish whether the necessary simultaneity of compression had been achieved. While there was at least one prominent scientist ( Ernest O. Lawrence ) who advocated for a full-scale test, by early 1945 Little Boy was regarded as nearly a sure thing and was expected to have a higher yield than the first-generation implosion bombs. Though Little Boy incorporated various safety mechanisms, an accidental detonation of

2415-462: A fully-assembled weapon was very possible. Should the bomber carrying the device crash, the hollow "bullet" could be driven into the "target" cylinder, possibly detonating the bomb from gravity alone (though tests suggested this was unlikely), but easily creating a critical mass that would release dangerous amounts of radiation. A crash of the B-29 and subsequent fire could trigger the explosives, causing

2576-421: A fusion weapon as of January 2016 , though this claim is disputed. Thermonuclear weapons are considered much more difficult to successfully design and execute than primitive fission weapons. Almost all of the nuclear weapons deployed today use the thermonuclear design because it results in an explosion hundreds of times stronger than that of a fission bomb of similar weight. Thermonuclear bombs work by using

2737-508: A high surface area and a rapid burning area, and could attain pressures of up to 40,000 pounds per square inch (280,000 kPa). Cordite for the wartime Little Boy was sourced from Canada; propellant for post-war Little Boys was obtained from the Picatinny Arsenal . The bomb contained 64 kilograms (141 lb) of enriched uranium. Most was enriched to 89% but some was only 50% uranium-235, for an average enrichment of 80%. Less than

2898-447: A kilogram of uranium underwent nuclear fission , and of this mass only 0.7 grams (0.025 oz) was transformed into several forms of energy, mostly kinetic energy , but also heat and radiation. 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 kilograms [85 lb]). It consisted of

3059-721: A large quantity of uranium that the overall distance through which daughter neutrons must travel has so many mean free paths it becomes very probable most neutrons will find uranium nuclei to collide with, before escaping the supercritical mass. The first time gun-type fission weapons were discussed was as part of the British Tube Alloys nuclear bomb development program, the world's first nuclear bomb development program. The British MAUD Report of 1941 laid out how "an effective uranium bomb which, containing some 25 lb of active material, would be equivalent as regards destructive effect to 1,800 tons of T.N.T". The bomb would use

3220-413: A lifelong increase in cancer risk. To date, no radiation-related evidence of heritable diseases has been observed among the survivors' children. After the surrender of Japan was finalized, Manhattan Project scientists began to immediately survey the city of Hiroshima to better understand the damage, and to communicate with Japanese physicians about radiation effects in particular. The collaboration became

3381-472: A nation's economic electronics-based infrastructure. Because the effect is most effectively produced by high altitude nuclear detonations (by military weapons delivered by air, though ground bursts also produce EMP effects over a localized area), it can produce damage to electronics over a wide, even continental, geographical area. Research has been done into the possibility of pure fusion bombs : nuclear weapons that consist of fusion reactions without requiring

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3542-537: A new nuclear strategy, one that is distinct from that which gave relative stability during the Cold War. Since 1996, the United States has had a policy of allowing the targeting of its nuclear weapons at terrorists armed with weapons of mass destruction . Robert Gallucci argues that although traditional deterrence is not an effective approach toward terrorist groups bent on causing a nuclear catastrophe, Gallucci believes that "the United States should instead consider

3703-425: A nuclear war between two nations would result in mutual annihilation. From this point of view, the significance of nuclear weapons is to deter war because any nuclear war would escalate out of mutual distrust and fear, resulting in mutually assured destruction . This threat of national, if not global, destruction has been a strong motivation for anti-nuclear weapons activism. Critics from the peace movement and within

3864-411: A nuclear weapon from another country by threatening nuclear retaliation is known as the strategy of nuclear deterrence . The goal in deterrence is to always maintain a second strike capability (the ability of a country to respond to a nuclear attack with one of its own) and potentially to strive for first strike status (the ability to destroy an enemy's nuclear forces before they could retaliate). During

4025-465: A nuclear weapon is a gravity bomb dropped from aircraft ; this was the method used by the United States against Japan in 1945. This method places few restrictions on the size of the weapon. It does, however, limit attack range, response time to an impending attack, and the number of weapons that a country can field at the same time. With miniaturization, nuclear bombs can be delivered by both strategic bombers and tactical fighter-bombers . This method

4186-409: A nuclear weapon to its target is an important factor affecting both nuclear weapon design and nuclear strategy . The design, development, and maintenance of delivery systems are among the most expensive parts of a nuclear weapons program; they account, for example, for 57% of the financial resources spent by the United States on nuclear weapons projects since 1940. The simplest method for delivering

4347-433: A nuclear weapon with suitable materials (such as cobalt or gold ) creates a weapon known as a salted bomb . This device can produce exceptionally large quantities of long-lived radioactive contamination . It has been conjectured that such a device could serve as a "doomsday weapon" because such a large quantity of radioactivities with half-lives of decades, lifted into the stratosphere where winds would distribute it around

4508-439: 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. Comparing this yield to the observed damage produced a rule of thumb called the 5 pounds per square inch (34  kPa ) lethal area rule. Approximately all the people inside the area where the shock wave carried such an overpressure or greater would be killed. At Hiroshima, that area

4669-421: A policy of expanded deterrence, which focuses not solely on the would-be nuclear terrorists but on those states that may deliberately transfer or inadvertently leak nuclear weapons and materials to them. By threatening retaliation against those states, the United States may be able to deter that which it cannot physically prevent.". Graham Allison makes a similar case, arguing that the key to expanded deterrence

4830-538: A probability of more than 1:2.52 of creating another fission. During the 1.35 ms of supercriticality prior to full assembly, there was a 10% probability of a fission, with somewhat less probability of pre-detonation. Initially the Manhattan Project gun-type effort was directed at making a gun weapon that used plutonium as its source of fissile material, known as the " Thin Man " because of its extreme length. It

4991-473: A propellent, or creating a "double gun" with two projectiles) were pursued in the early years of the project, while the facilities to manufacture fissile material were being constructed. The belief that the gun design would be an easy engineering task once fuel was available led to a sense of optimism at Los Alamos, although Oppenheimer established a small research group to study implosion as a fallback in early 1943. A full ordnance program for gun-design development

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5152-562: A repackaged W19 in a 16-inch (406 mm) shell for US Navy battleships, the W23 . The third family was an 8-inch (203 mm) artillery shell, the W33 . South Africa also developed six nuclear bombs based on the gun-type principle, and was working on missile warheads using the same basic design – See South Africa and weapons of mass destruction . There are currently no known gun-type weapons in service: advanced nuclear weapon states tended to abandon

5313-506: A second one sometime in December", assuming the second weapon would be a gun type; designing an implosion bomb for enriched uranium was considered, and this would increase the production rate. The enriched uranium projectile was completed on 15 June, and the target was completed on 24 July. The target and bomb pre-assemblies (partly assembled bombs without the fissile components) left Hunters Point Naval Shipyard , California, on 16 July aboard

5474-447: A significant portion of their energy from fission reactions used to "trigger" fusion reactions, and fusion reactions can themselves trigger additional fission reactions. Only six countries—the United States , Russia , the United Kingdom , China , France , and India —have conducted thermonuclear weapon tests. Whether India has detonated a "true" multi-staged thermonuclear weapon is controversial. North Korea claims to have tested

5635-537: 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. 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

5796-401: A stack of nine uranium rings, each 6.25 inches (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,

5957-550: A substantial investment" in the past to develop pure fusion weapons, but that, "The U.S. does not have and is not developing a pure fusion weapon", and that, "No credible design for a pure fusion weapon resulted from the DOE investment". Nuclear isomers provide a possible pathway to fissionless fusion bombs. These are naturally occurring isotopes ( Hf being a prominent example) which exist in an elevated energy state. Mechanisms to release this energy as bursts of gamma radiation (as in

6118-520: 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. Later calculations based on charring pointed to a yield of 13 to 14 kilotons. In 1953, Frederick Reines calculated the yield as 15 kilotons of TNT (63 TJ). Based on

6279-449: A tamper and neutron reflector of tungsten carbide and steel, both materials having a combined mass of 2,300 kilograms (5,100 lb). Neutron initiators inside the assembly were activated by the impact of the projectile into the target. The material was split almost in half, with at one end a group of rings of highly enriched uranium with 40% of the supercritical mass, and at the other end another group of slightly larger rings with 60% of

6440-484: A test structure in Nevada in 1953. 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. The first effect of the explosion was blinding light, accompanied by radiant heat from the fireball. The Hiroshima fireball was 1,200 feet (370 m) in diameter, with a surface temperature of 10,000 °F (6,000 °C), about

6601-420: Is a thermonuclear weapon that yields a relatively small explosion but a relatively large amount of neutron radiation . Such a weapon could, according to tacticians, be used to cause massive biological casualties while leaving inanimate infrastructure mostly intact and creating minimal fallout. Because high energy neutrons are capable of penetrating dense matter, such as tank armor, neutron warheads were procured in

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6762-456: Is analogous to identifying a criminal by fingerprints. "The goal would be twofold: first, to deter leaders of nuclear states from selling weapons to terrorists by holding them accountable for any use of their weapons; second, to give leaders every incentive to tightly secure their nuclear weapons and materials." According to the Pentagon's June 2019 " Doctrine for Joint Nuclear Operations " of

6923-403: Is coming up with ways of tracing nuclear material to the country that forged the fissile material. "After a nuclear bomb detonates, nuclear forensics cops would collect debris samples and send them to a laboratory for radiological analysis. By identifying unique attributes of the fissile material, including its impurities and contaminants, one could trace the path back to its origin." The process

7084-481: Is for the purpose of achieving different yields for different situations , and in manipulating design elements to attempt to minimize weapon size, radiation hardness or requirements for special materials, especially fissile fuel or tritium. Some nuclear weapons are designed for special purposes; most of these are for non-strategic (decisively war-winning) purposes and are referred to as tactical nuclear weapons . The neutron bomb purportedly conceived by Sam Cohen

7245-428: Is inherently dangerous to have a weapon containing a quantity and shape of fissile material that can form a critical mass through a relatively simple accident. Furthermore, if the weapon is dropped from an aircraft into the sea, then the moderating effect of the seawater can also cause a criticality accident without the weapon even being physically damaged. Neither can happen with an implosion-type weapon, since there

7406-503: Is no evidence that it is feasible beyond the military domain. However, the U.S. Air Force funded studies of the physics of antimatter in the Cold War , and began considering its possible use in weapons, not just as a trigger, but as the explosive itself. A fourth generation nuclear weapon design is related to, and relies upon, the same principle as antimatter-catalyzed nuclear pulse propulsion . Most variation in nuclear weapon design

7567-512: Is normally insufficient fissile material to form a critical mass without the correct detonation of the explosive lenses. The gun method has also been applied for nuclear artillery shells, since the simpler design can be more easily engineered to withstand the rapid acceleration and g-forces imparted by an artillery gun, and since the smaller diameter of the gun-type design can be relatively easily fitted to projectiles that can be fired from existing artillery. A US gun-type nuclear artillery weapon,

7728-409: Is not a fusion bomb. In the boosted bomb, the neutrons produced by the fusion reactions serve primarily to increase the efficiency of the fission bomb. There are two types of boosted fission bomb: internally boosted, in which a deuterium-tritium mixture is injected into the bomb core, and externally boosted, in which concentric shells of lithium-deuteride and depleted uranium are layered on the outside of

7889-490: Is not clear that this has ever been implemented, and their plausible use in nuclear weapons is a matter of dispute. The other basic type of nuclear weapon produces a large proportion of its energy in nuclear fusion reactions. Such fusion weapons are generally referred to as thermonuclear weapons or more colloquially as hydrogen bombs (abbreviated as H-bombs ), as they rely on fusion reactions between isotopes of hydrogen ( deuterium and tritium ). All such weapons derive

8050-470: Is purely the Pu isotope . Production of impurity-free plutonium is very difficult and is impractical. The required amount of uranium is relatively large, and thus the overall efficiency is relatively low. The main reason for this is the uranium metal does not undergo compression (and resulting density increase) as does the implosion design. Instead, gun-type bombs assemble the supercritical mass by amassing such

8211-454: Is the primary means of nuclear weapons delivery; the majority of U.S. nuclear warheads, for example, are free-fall gravity bombs, namely the B61 , which is being improved upon to this day. Preferable from a strategic point of view is a nuclear weapon mounted on a missile , which can use a ballistic trajectory to deliver the warhead over the horizon. Although even short-range missiles allow for

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8372-534: Is thought to only be usable with enriched uranium fuel. It is unknown though possible to make a composite design using high grade plutonium in the bullet only. After it was discovered that the "Thin Man" program would not be successful, Los Alamos redirected its efforts into creating the implosion-type plutonium weapon: " Fat Man ". The gun program switched completely over to developing a uranium bomb. Although in Little Boy 132 pounds (60 kg) of 80%-grade U

8533-637: The Atomic Bomb Casualty Commission in 1946, a joint U.S.–Japanese project to track radiation injuries among survivors. In 1975 its work was superseded by the Radiation Effects Research Foundation . In 1962, scientists at Los Alamos created a mockup of Little Boy known as "Project Ichiban" in order to answer some of the unanswered questions about the exact radiation output of the bomb, which would be useful for setting benchmarks for interpreting

8694-467: The B-29s to carry the two atomic bomb shapes as part of Project Silverplate in late 1943. Another explanation of the names, from a classified United States Air Force history of Project Silverplate from the 1950s, implies a possible reconciliation of the two versions: that the terms "Thin Man" and "Fat Man" were first developed by someone at or from Los Alamos (i.e., Serber), but were consciously adopted by

8855-476: The Hanford Site was designed to produce around 20 kilograms of plutonium per month, and each Fat Man bomb used around 6 kilograms of material.) Because of the simplicity of the gun-type design, laboratory testing could establish that its parts worked correctly on their own: for example, dummy projectiles could be shot down the gun barrel to make sure they were "seated" correctly onto a dummy target. Absence of

9016-827: The Naval Gun Factory in Washington, D.C.; the target case and some other components 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 . The bomb, except for the uranium payload, was ready at the beginning of May 1945. Manhattan District Engineer Kenneth Nichols expected on 1 May 1945 to have enriched uranium "for one weapon before August 1 and

9177-695: The Starfish Prime high-altitude nuclear test in 1962, an unexpected effect was produced which is called a nuclear electromagnetic pulse . This is an intense flash of electromagnetic energy produced by a rain of high-energy electrons which in turn are produced by a nuclear bomb's gamma rays. This flash of energy can permanently destroy or disrupt electronic equipment if insufficiently shielded. It has been proposed to use this effect to disable an enemy's military and civilian infrastructure as an adjunct to other nuclear or conventional military operations. By itself it could as well be useful to terrorists for crippling

9338-496: The Strategic Bombing Survey estimated that the same blast and fire effect could have been caused by 2.1 kilotons of conventional bombs distributed evenly over the same target area: "220 B-29s carrying 1.2 kilotons of incendiary bombs , 400 tons of high-explosive bombs, and 500 tons of anti-personnel fragmentation bombs ." Since the target was spread across a two-dimensional plane, the vertical component of

9499-461: The Treaty on the Non-Proliferation of Nuclear Weapons (1968) attempted to place restrictions on the types of activities signatories could participate in, with the goal of allowing the transference of non-military nuclear technology to member countries without fear of proliferation. Gun-type fission weapon Since it is a relatively slow method of assembly, plutonium cannot be used unless it

9660-493: The Trinity nuclear test . There were several reasons for not testing a Little Boy type of device. Primarily, there was the issue of fissile material availability. K-25 at Clinton Engineer Works was designed to produce around 30 kilograms of enriched uranium per month, and the Little Boy design used over 60 kilograms per bomb. So testing the weapon would incur a considerable delay in use of the weapon. (By comparison, B Reactor at

9821-554: The Tsar Bomba (see TNT equivalent ). A thermonuclear weapon weighing as little as 600 pounds (270 kg) can release energy equal to more than 1.2 megatonnes of TNT (5.0 PJ). A nuclear device no larger than a conventional bomb can devastate an entire city by blast, fire, and radiation . Since they are weapons of mass destruction , the proliferation of nuclear weapons is a focus of international relations policy. Nuclear weapons have been deployed twice in war , both by

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9982-676: The Tsar Bomba of the USSR, which released an energy equivalent of over 50 megatons of TNT (210 PJ), was a three-stage weapon. Most thermonuclear weapons are considerably smaller than this, due to practical constraints from missile warhead space and weight requirements. In the early 1950s the Livermore Laboratory in the United States had plans for the testing of two massive bombs, Gnomon and Sundial , 1 gigaton of TNT and 10 gigatons of TNT respectively. Fusion reactions do not create fission products, and thus contribute far less to

10143-677: The W9 , was tested on May 25, 1953, at the Nevada Test Site . Fired as part of Operation Upshot–Knothole and codenamed Shot GRABLE , a 280 mm (11 in) shell was fired 10,000 m (33,000 ft) and detonated 160 m (520 ft) above the ground with an estimated yield of 15 kilotons . This is approximately the same yield as Little Boy , although the W9 had less than 1 ⁄ 10 of Little Boy's weight (365 kg vs. 4,000 kg, or 805 lbs vs. 8,819 lbs). The shell

10304-424: The hafnium controversy ) have been proposed as possible triggers for conventional thermonuclear reactions. Antimatter , which consists of particles resembling ordinary matter particles in most of their properties but having opposite electric charge , has been considered as a trigger mechanism for nuclear weapons. A major obstacle is the difficulty of producing antimatter in large enough quantities, and there

10465-614: The head of government or head of state . Despite controls and regulations governing nuclear weapons, there is an inherent danger of "accidents, mistakes, false alarms, blackmail, theft, and sabotage". In the late 1940s, lack of mutual trust prevented the United States and the Soviet Union from making progress on arms control agreements. The Russell–Einstein Manifesto was issued in London on July 9, 1955, by Bertrand Russell in

10626-452: The heavy cruiser USS  Indianapolis , arriving on 26 July. The target inserts followed by air on 30 July. Although all of its components had been individually tested, 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 fissile material, which took place on 16 July 1945 at

10787-503: The nuclear fission of uranium-235 , whereas Thin Man was based on fission of plutonium-239 . Fission was accomplished by shooting a hollow cylinder (the "bullet") onto a solid cylinder of the same material (the "target") by means of a charge of nitrocellulose propellant powder. Little Boy contained 64 kilograms (141 lb) of highly enriched uranium , although less than a kilogram underwent nuclear fission. Its components were fabricated at three different plants so that no one would have

10948-436: The tropopause into the stratosphere , where the calm non-turbulent winds permit the debris to travel great distances from the burst, eventually settling and unpredictably contaminating areas far removed from the target of the explosion. There are other types of nuclear weapons as well. For example, a boosted fission weapon is a fission bomb that increases its explosive yield through a small number of fusion reactions, but it

11109-591: The "Fat Man." In September 1945, another Project Alberta physicist, Norman F. Ramsey , stated in his brief "History of Project A," that the early bomb ballistic test shapes designs were referred to as "Thin Man" and "Fat Man" by (unspecified) " Air Force representatives" for "security reasons," so that their communications over telephones sounded "as if they were modifying a plane to carry Roosevelt (the Thin Man) and Churchill (the Fat Man)," as opposed to modifying

11270-537: The "implosion" method, is more sophisticated and more efficient (smaller, less massive, and requiring less of the expensive fissile fuel) than the former. A major challenge in all nuclear weapon designs is to ensure that a significant fraction of the fuel is consumed before the weapon destroys itself. The amount of energy released by fission bombs can range from the equivalent of just under a ton to upwards of 500,000 tons (500 kilotons ) of TNT (4.2 to 2.1 × 10  GJ). All fission reactions generate fission products ,

11431-586: The 1980s (though not deployed in Europe) for use as tactical payloads for US Army artillery shells (200 mm W79 and 155 mm W82 ) and short range missile forces. Soviet authorities announced similar intentions for neutron warhead deployment in Europe; indeed, they claimed to have originally invented the neutron bomb, but their deployment on USSR tactical nuclear forces is unverifiable. A type of nuclear explosive most suitable for use by ground special forces

11592-414: The 5 pounds per square inch (34 kPa) contour at 1.1 miles (1.8 km). Later test explosions of nuclear weapons with houses and other test structures nearby confirmed the 5 psi overpressure threshold. Ordinary urban buildings experiencing it were 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

11753-620: The 70 spontaneous fissions per second, this only causes a delay of a few times 1/70 second, which in this case does not matter. Initiators were only added to Little Boy late in its design. With regard to the risk of proliferation and use by terrorists , the relatively simple design is a concern, as it does not require as much fine engineering or manufacturing as other methods. With enough highly enriched uranium, nations or groups with relatively low levels of technological sophistication could create an inefficient—though still quite powerful—gun-type nuclear weapon. For technologically advanced states

11914-425: The Cold War, policy and military theorists considered the sorts of policies that might prevent a nuclear attack, and they developed game theory models that could lead to stable deterrence conditions. Different forms of nuclear weapons delivery (see above) allow for different types of nuclear strategies. The goals of any strategy are generally to make it difficult for an enemy to launch a pre-emptive strike against

12075-498: The Hiroshima bomb to make an accurate model, corrected earlier published accounts. The fuzing system was designed to trigger at the most destructive altitude, which calculations suggested was 1,900 feet (580 m). It employed a three-stage interlock system: The Little Boy pre-assemblies were designated L-1, L-2, L-3, L-4, L-5, L-6, L-7, and L-11. Of these, L-1, L-2, L-5, and L-6 were expended in test drops. The first drop test

12236-494: The Joint Chiefs of Staffs website Publication, "Integration of nuclear weapons employment with conventional and special operations forces is essential to the success of any mission or operation." Because they are weapons of mass destruction, the proliferation and possible use of nuclear weapons are important issues in international relations and diplomacy. In most countries, the use of nuclear force can only be authorized by

12397-504: The Little Boy design, the U-235 "bullet" had a mass of around 86 pounds (39 kg), and it was 7 inches (17.8 cm) long, with a diameter of 6.25 inches (15.9 cm). The hollow cylindrical shape made it subcritical. It was powered by a cordite charge. The uranium target spike was about 57.3 pounds (26 kg). Both the bullet and the target consisted of multiple rings stacked together. The use of "rings" had two advantages: it allowed

12558-430: The Little Boy mechanism assumed that a small, solid projectile was fired into the center of a larger, stationary target. However, critical mass considerations dictated that in Little Boy the more extensive, hollow piece would be the projectile. Hollow cylinders have higher critical masses than solid pieces of fissile material, because any neutrons encountered by or generated by the material are more likely to get scattered in

12719-466: The Mark 8 and Mark 11 designs were intended for use as earth-penetrating bombs (see nuclear bunker buster ), for which the gun-type method was preferred for a time by designers who were less than certain that early implosion-type weapons would successfully detonate following an impact. The second program was a family of 11-inch (280 mm) nuclear artillery shells, the W9 and its derivative W19 , plus

12880-589: The Nagasaki bomb detonated 2.0 miles (3.2 km) from the city center over hilly terrain that was partially bare of buildings. In Hiroshima, almost everything within 1.0 mile (1.6 km) 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. The perimeter of severe blast damage approximately followed

13041-503: The Nuclear Age (1961) that mere possession of a nuclear arsenal was enough to ensure deterrence, and thus concluded that the spread of nuclear weapons could increase international stability . Some prominent neo-realist scholars, such as Kenneth Waltz and John Mearsheimer , have argued, along the lines of Gallois, that some forms of nuclear proliferation would decrease the likelihood of total war , especially in troubled regions of

13202-502: The Project Ichiban data, and the pressure-wave data from The Great Artiste , the yield was estimated in the 1960s at 16.6 ± 0.3 kilotons. A review conducted by a scientist at Los Alamos in 1985 concluded, on the basis of existing blast, thermal, and radiological data, and then-current models of weapons effects, that the best estimate of the yield was 15 kilotons of TNT (63 TJ) with an uncertainty of 20% (±3 kt). By comparison,

13363-608: The USAAF detonated a plutonium implosion-type fission bomb nicknamed " Fat Man " over the Japanese city of Nagasaki . These bombings caused injuries that resulted in the deaths of approximately 200,000 civilians and military personnel . The ethics of these bombings and their role in Japan's surrender are to this day, still subjects of debate . Since the atomic bombings of Hiroshima and Nagasaki , nuclear weapons have been detonated over 2,000 times for testing and demonstration. Only

13524-777: The USAF AIR-2 Genie , the AIM-26 Falcon and US Army Nike Hercules . Missile interceptors such as the Sprint and the Spartan also used small nuclear warheads (optimized to produce neutron or X-ray flux) but were for use against enemy strategic warheads. Other small, or tactical, nuclear weapons were deployed by naval forces for use primarily as antisubmarine weapons. These included nuclear depth bombs or nuclear armed torpedoes. Nuclear mines for use on land or at sea are also possibilities. The system used to deliver

13685-527: The United States against the Japanese cities of Hiroshima and Nagasaki in 1945 during World War II . Nuclear weapons have only twice been used in warfare, both times by the United States against Japan at the end of World War II . On August 6, 1945, the United States Army Air Forces (USAAF) detonated a uranium gun-type fission bomb nicknamed " Little Boy " over the Japanese city of Hiroshima ; three days later, on August 9,

13846-526: The United States. Small, two-man portable tactical weapons (somewhat misleadingly referred to as suitcase bombs ), such as the Special Atomic Demolition Munition , have been developed, although the difficulty of combining sufficient yield with portability limits their military utility. Nuclear warfare strategy is a set of policies that deal with preventing or fighting a nuclear war. The policy of trying to prevent an attack by

14007-456: The air than to continue a chain reaction. The larger piece would also avoid the effects of neutron reflection from the tungsten carbide tamper until it was fully joined with the rest of the fuel. Once joined and with its neutrons reflected, the assembled fissile core would comprise more than two critical masses of uranium-235. In 2004, John Coster-Mullen , a truck driver and model maker from Illinois who had studied every photograph and document on

14168-488: The atomic bomb would not be difficult to design and that the difficulty would lie only in the production of fuel. Calculations in mid-1942 by theoretical physicists working on the project reinforced the idea that an ordinary artillery gun barrel would be able to impart sufficient velocity to the fissile material projectile. Several different weapon designs, including autocatalytic assembly, a nascent version of implosion, and alternative gun designs (e.g., using high explosives as

14329-428: The best value for the Nagasaki bomb was evaluated as 21 kilotons of TNT (88 TJ) with an uncertainty of 10% (±2 kt), the difference in uncertainty owing to having better data on the latter. To put these numerical differences into context, it is necessary to know that the acute effects of nuclear detonations, especially the blast and thermal effects, do not scale linearly, but generally as a cubic root . Specifically,

14490-436: 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

14651-558: The bomb was test dropped near Tinian. L-11 was the assembly used for the Hiroshima bomb, and was fully assembled with its nuclear fuel by 31 July. Parsons, the Enola Gay ' s weaponeer, was concerned about the possibility of an accidental detonation if the plane crashed on takeoff, so he decided not to load the four cordite powder bags into the gun breech until the aircraft was in flight. After takeoff, Parsons and his assistant, Second Lieutenant Morris R. Jeppson , made their way into

14812-417: The bomber used was the one subsequently known as Jabit . L-6 was used as a dress rehearsal on 29 July. 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 31 July, but this time L-6 was reloaded onto a different B-29, Enola Gay , piloted by Tibbets, and

14973-417: The chain reaction is slower when the supercriticality is low, it still happens in a time so brief that the bullet hardly moves in that time. This could cause a fizzle , a predetonation which would blow the material apart before creating much of an explosion. Thus, it is important that the frequency at which free neutrons occur is kept low, compared with the assembly time from this point. This also means that

15134-485: The chance of a successful missile defense . Today, missiles are most common among systems designed for delivery of nuclear weapons. Making a warhead small enough to fit onto a missile, though, can be difficult. Tactical weapons have involved the most variety of delivery types, including not only gravity bombs and missiles but also artillery shells, land mines , and nuclear depth charges and torpedoes for anti-submarine warfare . An atomic mortar has been tested by

15295-404: The city. The Hiroshima bombing was the second nuclear explosion in history, after the Trinity nuclear test . Little Boy was developed by Lieutenant Commander Francis Birch 's group at the Manhattan Project 's Los Alamos Laboratory during World War II, a reworking of their abandoned Thin Man nuclear bomb. Like Thin Man, it was a gun-type fission weapon . It derived its explosive power from

15456-475: The conditions for a large-scale explosion. As a consequence of the discovery of the Pu-240 contamination problem, in July 1944 almost all research at Los Alamos was redirected to the implosion-type plutonium weapon, and the laboratory was entirely reorganized around the implosion problem. Work on the gun-type weapon continued under Person's Ordnance (O) Division, for use exclusively with highly enriched uranium as

15617-518: The correct drawings and parts, and figured out how they went together. Eventually, they built six Little Boy assemblies. Although the casings, barrels, and components were tested, no enriched uranium was supplied for the bombs. By early 1947, the problem caused by the Wigner effect was on its way to solution, and the three officers were reassigned. The Navy Bureau of Ordnance began in 1947 to produce 25 "revised" Little Boy mechanical assemblies for use by

15778-463: 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 meters (1,900 ft) above the ground, there was no bomb crater and no local radioactive fallout. However, a burst of intense neutron and gamma radiation came directly from

15939-435: The creation of nuclear fallout than fission reactions, but because all thermonuclear weapons contain at least one fission stage, and many high-yield thermonuclear devices have a final fission stage, thermonuclear weapons can generate at least as much nuclear fallout as fission-only weapons. Furthermore, high yield thermonuclear explosions (most dangerously ground bursts) have the force to lift radioactive debris upwards past

16100-494: 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. Later estimates put the deaths as high as 140,000 people. The United States Strategic Bombing Survey estimated that out of 24,158 Imperial Japanese Army soldiers in Hiroshima at

16261-455: The decision process. The prospect of mutually assured destruction might not deter an enemy who expects to die in the confrontation. Further, if the initial act is from a stateless terrorist instead of a sovereign nation, there might not be a nation or specific target to retaliate against. It has been argued, especially after the September 11, 2001, attacks , that this complication calls for

16422-433: The design in favor of the implosion-type weapons , boosted fission weapons , and thermonuclear weapons . New nuclear weapon states tend to develop boosted fission and thermonuclear weapons only. All known gun-type nuclear weapons previously built worldwide have been dismantled. The "gun" method is roughly how the Little Boy weapon, which was detonated over Hiroshima , worked, using uranium-235 as its fissile material. In

16583-557: The detonation, these fires had merged into a firestorm , pulling in surface air from all directions to feed an inferno which consumed everything flammable. The Hiroshima firestorm was roughly 2.0 miles (3.2 km) in diameter, corresponding closely to the severe blast-damage zone. (See the USSBS map, right.) Blast-damaged buildings provided fuel for the fire. Structural lumber and furniture were splintered and scattered about. Debris-choked roads obstructed firefighters. Broken gas pipes fueled

16744-428: The distance of these effects scale as a function of the yield raised to an exponential power of 1 ⁄ 3 . So the range of the 5 pounds per square inch (34 kPa) overpressure damage expected from a detonated 12 kiloton weapon with a height of burst at 1,968 feet (600 m) would be expected to be 0.98 miles (1.58 km), whereas a 20 kiloton weapon would have the same range extend to 1.12 miles (1.80 km),

16905-427: The dragon's tail "). In any event, it could not be tested before being deployed, as there was only sufficient U-235 available for one device. Even though the design was never proof-tested, there was thought to be no risk of the device being captured by an enemy if it malfunctioned. Even a "fizzle" would have completely disintegrated the device, while the multiple redundancies built into the "Little Boy" design meant there

17066-436: The edge of the blast-damaged area, encountering less available fuel. 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." Local fallout is dust and ash from a bomb crater, contaminated with radioactive fission products. It falls to earth downwind of

17227-594: The emptied casing to the Smithsonian in 1993. Three other disarmed bombs are on display in the United States; another is at the Imperial War Museum in London. Atomic bomb A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions , either fission (fission bomb) or a combination of fission and fusion reactions ( thermonuclear bomb ), producing

17388-464: The end of 1948, and only two outer casings were available. By the end of 1950, only five complete Little Boy assemblies had been built. All were retired by November 1950. The Smithsonian Institution displayed a Little Boy (complete, except for enriched uranium), until 1986. The Department of Energy took the weapon from the museum to remove its inner components, so the bomb could not be stolen and detonated with fissile material. The government returned

17549-469: The energy of a fission bomb to compress and heat fusion fuel. In the Teller-Ulam design , which accounts for all multi-megaton yield hydrogen bombs, this is accomplished by placing a fission bomb and fusion fuel ( tritium , deuterium , or lithium deuteride ) in proximity within a special, radiation-reflecting container. When the fission bomb is detonated, gamma rays and X-rays emitted first compress

17710-438: The fire, and broken water pipes rendered hydrants useless. At Nagasaki, the fires failed to merge into a single firestorm, and the fire-damaged area was only one-quarter as great as at Hiroshima, due in part to a southwest wind that pushed the fires away from the city. 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

17871-502: The first atomic bombs got their names. Los Alamos Laboratory and Project Alberta physicist Robert Serber stated, many decades after the fact, that he had named the first two atomic bomb designs during World War II based on their shapes: Thin Man and Fat Man . The "Thin Man" was a long, thin device, and its name came from the Dashiell Hammett detective novel and series of movies about The Thin Man . The "Fat Man"

18032-455: The fission bomb core. The external method of boosting enabled the USSR to field the first partially thermonuclear weapons, but it is now obsolete because it demands a spherical bomb geometry, which was adequate during the 1950s arms race when bomber aircraft were the only available delivery vehicles. The detonation of any nuclear weapon is accompanied by a blast of neutron radiation . Surrounding

18193-494: The fission of the uranium. Its lethal radius was approximately 1.3 kilometers (0.8 mi), 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. Among injured survivors, 30% had radiation injuries from which they recovered, but with

18354-420: The fusion fuel, then heat it to thermonuclear temperatures. The ensuing fusion reaction creates enormous numbers of high-speed neutrons , which can then induce fission in materials not normally prone to it, such as depleted uranium . Each of these components is known as a "stage", with the fission bomb as the "primary" and the fusion capsule as the "secondary". In large, megaton-range hydrogen bombs, about half of

18515-535: The globe, would make all life on the planet extinct. In connection with the Strategic Defense Initiative , research into the nuclear pumped laser was conducted under the DOD program Project Excalibur but this did not result in a working weapon. The concept involves the tapping of the energy of an exploding nuclear bomb to power a single-shot laser that is directed at a distant target. During

18676-455: The gun-type design "to bring the two halves together at high velocity and it is proposed to do this by firing them together with charges of ordinary explosive in a form of double gun". The method was applied in four known US programs. First, the " Little Boy " weapon which was detonated over Hiroshima and several additional units of the same design prepared after World War II, in 40 Mark 8 bombs, and their replacement, 40 Mark 11 bombs. Both

18837-498: The gun-type method is now essentially obsolete, for reasons of efficiency and safety (discussed above). The gun type method was largely abandoned by the United States as soon as the implosion technique was perfected, though it was retained in the specialised role of nuclear artillery for a time. Other nuclear powers, such as the United Kingdom and Soviet Union , never built an example of this type of weapon. Besides requiring

18998-491: The larger bullet to confidently remain subcritical (the hollow column served to keep the material from having too much contact with other material), and it allowed sub-critical assemblies to be tested using the same bullet but with just one ring. The barrel had an inside diameter of 6.5 inches (16.5 cm). Its length was 70.8 inches (1.8 m), which allowed the bullet to accelerate to its final speed of about 1,000 feet per second (300 m/s) before coming into contact with

19159-496: The majority of their energy from nuclear fission reactions alone, and those that use fission reactions to begin nuclear fusion reactions that produce a large amount of the total energy output. All existing nuclear weapons derive some of their explosive energy from nuclear fission reactions. Weapons whose explosive output is exclusively from fission reactions are commonly referred to as atomic bombs or atom bombs (abbreviated as A-bombs ). This has long been noted as something of

19320-407: The midst of the Cold War. It highlighted the dangers posed by nuclear weapons and called for world leaders to seek peaceful resolutions to international conflict. The signatories included eleven pre-eminent intellectuals and scientists, including Albert Einstein , who signed it just days before his death on April 18, 1955. A few days after the release, philanthropist Cyrus S. Eaton offered to sponsor

19481-545: The military establishment have questioned the usefulness of such weapons in the current military climate. According to an advisory opinion issued by the International Court of Justice in 1996, the use of (or threat of use of) such weapons would generally be contrary to the rules of international law applicable in armed conflict, but the court did not reach an opinion as to whether or not the threat or use would be lawful in specific extreme circumstances such as if

19642-408: The missiles before they land or implementing civil defense measures using early-warning systems to evacuate citizens to safe areas before an attack. Weapons designed to threaten large populations or to deter attacks are known as strategic weapons . Nuclear weapons for use on a battlefield in military situations are called tactical weapons . Critics of nuclear war strategy often suggest that

19803-643: The nuclear-capable Lockheed P2V Neptune aircraft carrier aircraft (which could be launched from, but not land on, the Midway -class aircraft carriers ). 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. However, no actual fissionable components were produced by

19964-480: The officers in Silverplate when they were adopting their own codenames for their own project (including "Silverplate"). As Silverplate involved modifying B-29s for a secret purpose, deliberately using codenames that would align with modifying vehicles for Roosevelt and Churchill would serve their needs well. Because of its perceived simplicity, the gun-type nuclear weapon design was the first approach pursued by

20125-425: The presence of the isotope plutonium-240 (Pu-240) raised the rate of spontaneous fission of the plutonium to an unacceptable amount. Previous analyses of plutonium had been made from samples created by cyclotrons and did not have as much of the contaminating isotope. If reactor-bred plutonium was used in a gun-type design, they concluded, it would predetonate , causing the weapon to destroy itself before achieving

20286-461: The projectile rings that were slid over a 1-inch rod. This rod then extended forward through the tungsten carbide plug, impact-absorbing anvil, and nose plug backstop, eventually protruding out of the front of the bomb casing. This entire target assembly was secured at both ends with locknuts. 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

20447-405: The projectile slug was pushed 42 inches (1,100 mm) along the 72-inch-long (1,800 mm), 6.5-inch-wide (170 mm) smooth-bore gun barrel. The slug "insert" was a 4-inch cylinder, 7 inches in length with a 1-inch (25 mm) axial hole. The slug comprised 40% of the total fissile mass (25.6 kilograms or 56 pounds). The insert was a stack of six washer-like uranium discs somewhat thicker than

20608-447: The projectile, since only the projectile's back end was in contact with the tamper prior to detonation. The rest of the tungsten carbide tamper 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. For the first fifty years after 1945, every published description and drawing of

20769-507: The prospect of no more plutonium for new cores and no more polonium for the initiators for the cores that had already been produced, the Director of the Manhattan Project, Major General Leslie R. Groves , ordered that some Little Boys be prepared as an interim measure until a solution 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

20930-451: The relationship between radiation exposure and later health outcomes. 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. After hostilities ended,

21091-428: The remains of the split atomic nuclei. Many fission products are either highly radioactive (but short-lived) or moderately radioactive (but long-lived), and as such, they are a serious form of radioactive contamination . Fission products are the principal radioactive component of nuclear fallout . Another source of radioactivity is the burst of free neutrons produced by the weapon. When they collide with other nuclei in

21252-490: The same temperature as at the surface of the sun. Near ground zero, everything flammable burst into flame. One famous, anonymous Hiroshima victim, sitting on stone steps 850 feet (260 m) from the hypocenter, left a permanent shadow , having absorbed the fireball heat that permanently bleached the surrounding stone. Simultaneous fires were started throughout the blast-damaged area by fireball heat and by overturned stoves and furnaces, electrical shorts, etc. Twenty minutes after

21413-554: The scientists working on bomb design during the Manhattan Project . In 1942, it was not yet known which of the two fissile materials pathways being simultaneously pursued— uranium-235 or plutonium-239 —would be successful, or if there were significant differences between the two fuels that would impact the design work. Coordination with British scientists in May 1942 convinced the American scientists, led by J. Robert Oppenheimer , that

21574-491: The speed of the projectile must be sufficiently high; its speed can be increased but this requires a longer and heavier barrel, or a higher pressure of the propellant gas for greater acceleration of the bullet subcritical mass. In the case of Little Boy, the 20% U in the uranium had 70 spontaneous fissions per second. With the fissionable material in a supercritical state, each gave a large probability of detonation: each fission creates on average 2.52 neutrons, which each have

21735-439: The supercritical mass, which was fired onto the smaller group, with four polonium-beryllium neutron initiators to make the supercritical mass explode. A hole in the center of the larger piece dispersed the mass and increased the surface area, allowing more fission neutrons to escape, thus preventing a premature chain reaction. But, for this larger, hollow piece to have minimal contact with the tungsten carbide tamper , it must be

21896-402: The surrounding material, the neutrons transmute those nuclei into other isotopes, altering their stability and making them radioactive. The most commonly used fissile materials for nuclear weapons applications have been uranium-235 and plutonium-239 . Less commonly used has been uranium-233 . Neptunium-237 and some isotopes of americium may be usable for nuclear explosives as well, but it

22057-498: The survival of the state were at stake. Another deterrence position is that nuclear proliferation can be desirable. In this case, it is argued that, unlike conventional weapons, nuclear weapons deter all-out war between states, and they succeeded in doing this during the Cold War between the U.S. and the Soviet Union . In the late 1950s and early 1960s, Gen. Pierre Marie Gallois of France, an adviser to Charles de Gaulle , argued in books like The Balance of Terror: Strategy for

22218-416: The target. When the bullet is at a distance of 9.8 inches (25 cm), the combination becomes critical. This means that some free neutrons may cause the chain reaction to take place before the material could be fully joined (see nuclear chain reaction ). Typically the chain reaction takes less than 1 μs (100 shakes ), during which time the bullet travels only 0.3 mm ( 1 ⁄ 85 inch). Although

22379-553: The time of the bombing, 6,789 were killed or missing as a result of the bombing. The exact measurement of the explosive yield of the bomb 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

22540-614: The use of highly enriched U-235, the technique has other severe limitations. The implosion technique is much better suited to the various methods employed to reduce the mass of the weapon and increase the proportion of material which fissions. Apartheid South Africa built around five gun-type weapons, and no implosion-type weapons. They later abandoned their nuclear weapon program altogether. They were unique in their abandonment of nuclear weapons, and probably also by building gun-type weapons rather than implosion-type weapons. There are also safety problems with gun-type weapons. For example, it

22701-555: The various components, and stocks of spare parts. 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

22862-520: The war. A 1985 study estimated the bomb's yield was around 15 kilotons of TNT (63 TJ). 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. 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

23023-446: The weapon system and difficult to defend against the delivery of the weapon during a potential conflict. This can mean keeping weapon locations hidden, such as deploying them on submarines or land mobile transporter erector launchers whose locations are difficult to track, or it can mean protecting weapons by burying them in hardened missile silo bunkers. Other components of nuclear strategies included using missile defenses to destroy

23184-403: The weapon to detonate. If immersed in water, the uranium components were subject to a neutron moderator effect, which would not cause an explosion but would release radioactive contamination . For this reason, pilots were advised to crash on land rather than at sea. Ultimately, Parsons opted to keep the explosives out of the Little Boy bomb until after the B-29 had taken off, to avoid the risk of

23345-470: The weapon to fit into a B-29 bomb bay without difficulty. Though not an optimal use of fissile material compared to the implosion design, it was seen as a nearly guaranteed weapon. 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

23506-489: The work to Naval Captain William Sterling Parsons , who, along with Ed McMillan , Charles Critchfield , and Joseph Hirschfelder would be responsible for rendering the theory into practice. Concern that impurities in reactor-bred plutonium would make predetonation more likely meant that much of the gun-design work was focused on the plutonium gun. To achieve high projectile velocities, the plutonium gun

23667-631: The world where there exists a single nuclear-weapon state. Aside from the public opinion that opposes proliferation in any form, there are two schools of thought on the matter: those, like Mearsheimer, who favored selective proliferation, and Waltz, who was somewhat more non- interventionist . Interest in proliferation and the stability-instability paradox that it generates continues to this day, with ongoing debate about indigenous Japanese and South Korean nuclear deterrent against North Korea . The threat of potentially suicidal terrorists possessing nuclear weapons (a form of nuclear terrorism ) complicates

23828-624: The yield comes from the final fissioning of depleted uranium. Virtually all thermonuclear weapons deployed today use the "two-stage" design described to the right, but it is possible to add additional fusion stages—each stage igniting a larger amount of fusion fuel in the next stage. This technique can be used to construct thermonuclear weapons of arbitrarily large yield. This is in contrast to fission bombs, which are limited in their explosive power due to criticality danger (premature nuclear chain reaction caused by too-large amounts of pre-assembled fissile fuel). The largest nuclear weapon ever detonated,

23989-519: Was 1,384 mm (54.5 in) long. This was the only nuclear artillery shell ever actually fired (from an artillery gun) in the US test program. It was fired from a specially built artillery piece, nicknamed Atomic Annie . Eighty shells were produced from 1952 to 1953. It was retired in 1957. The W19 was also a 280 mm gun-type nuclear shell, a longer version of the W-9. Eighty warheads were produced and

24150-605: Was 17 feet (5.2 m) long with a narrow diameter (suggesting its codename as the Thin Man) which created considerable difficulty in its ballistics dropping from aircraft and fitting it into the bomb bay of a B-29. In early 1944, Emilio G. Segrè and his P-5 Group at Los Alamos received the first samples of plutonium produced from a nuclear reactor, the X-10 Graphite Reactor at Clinton Engineer Works in Oak Ridge, Tennessee . Analyzing it, they discovered that

24311-518: Was 2.2 miles (3.5 km) in diameter. The damage came from three main effects: blast, fire, and radiation. The blast from a nuclear bomb is the result of X-ray -heated air (the fireball) sending a shock wave or pressure wave in all directions, initially at a velocity greater than the speed of sound, 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

24472-471: Was conducted with L-1 on 23 July 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 24 and 25 July, using the L-2 and L-5 units in order to test all components. Tibbets was the pilot for both missions, but this time

24633-449: Was established by March 1943, with expertise provided by E.L. Rose , an experienced gun designer and engineer. Work was begun to study the properties of barrels, internal and external ballistics , and tampers of gun weapons. Oppenheimer led aspects of the effort, telling Rose that "at the present time [May 1945] our estimates are so ill founded that I think it better for me to take responsibility for putting them forward." He soon delegated

24794-436: Was negligible, if any, potential for the device to strike the ground without detonating at all. For a quick start of the chain reaction at the right moment a neutron trigger/initiator is used. An initiator is not strictly necessary for an effective gun design, as long as the design uses "target capture" (in essence, ensuring that the two subcritical masses, once fired together, cannot come apart until they explode). Considering

24955-407: Was not known until the postwar years when Ted Taylor developed an implosion design known as "Scorpion". The scientists who designed the "Little Boy" weapon were confident enough of its success that they did not field-test a design before using it in war (though scientists such as Louis Slotin did perform non-destructive tests with sub-critical assemblies, dangerous experiments nicknamed " tickling

25116-468: Was round and fat so it was named after Kasper Gutman, a rotund character in Hammett's 1930 novel The Maltese Falcon , played by Sydney Greenstreet in the 1941 film version . Little Boy was named by others as an allusion to Thin Man since it was based on its design. It was also sometimes referred to as the "Mark I" nuclear bomb design, with "Mark II" referring to the abandoned Thin Man, and "Mark III" to

25277-744: Was the Special Atomic Demolition Munition , or SADM, sometimes popularly known as a suitcase nuke . This is a nuclear bomb that is man-portable, or at least truck-portable, and though of a relatively small yield (one or two kilotons) is sufficient to destroy important tactical targets such as bridges, dams, tunnels, important military or commercial installations, etc. either behind enemy lines or pre-emptively on friendly territory soon to be overtaken by invading enemy forces. These weapons require plutonium fuel and are particularly "dirty". They also demand especially stringent security precautions in their storage and deployment. Small "tactical" nuclear weapons were deployed for use as antiaircraft weapons. Examples include

25438-454: Was then fully armed. Jeppson monitored the bomb's circuits. The bomb was dropped at approximately 08:15 (JST) on 6 August 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

25599-408: 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. More rigorous estimates of the bomb yield and conventional bomb equivalent were made when more data was acquired following the end of

25760-411: Was thought that if a plutonium gun-type bomb could be created, then the uranium gun-type bomb would be very easy to make by comparison. However, it was discovered in April 1944 that reactor -bred plutonium ( Pu-239 ) is contaminated with another isotope of plutonium, Pu-240 , which increases the material's spontaneous neutron-release rate, making pre-detonation inevitable. For this reason, a gun-type bomb

25921-479: Was used (hence 106 pounds or 48 kilograms), the minimum is about 44 to 55 pounds (20 to 25 kg), versus 33 pounds (15 kg) for the implosion method. Little Boy's target subcritical mass was enclosed in a neutron reflector made of tungsten carbide (WC). The presence of a neutron reflector reduced neutron losses during the chain reaction, and so reduced the quantity of uranium fuel needed. A more effective reflector material would be metallic beryllium, but this

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