134-541: Monturaqui is an impact crater in Chile . It lies south of the Salar de Atacama and was formed 663,000 ± 90,000 years ago by the impact of an IAB meteorite . It is 350 m × 370 m (1,150 ft × 1,210 ft) wide and 34 m (112 ft) deep and contains a salt pan . Only a few remnants of the meteorite that formed the crater have been collected, with most of the rocks being of local origin. The crater
268-400: 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
402-433: A paraboloid (bowl-shaped) crater in which the centre has been pushed down, a significant volume of material has been ejected, and a topographically elevated crater rim has been pushed up. When this cavity has reached its maximum size, it is called the transient cavity. The depth of the transient cavity is typically a quarter to a third of its diameter. Ejecta thrown out of the crater do not include material excavated from
536-468: A certain altitude (retardation point), and start to accelerate again due to Earth's gravity until the body reaches its terminal velocity of 0.09 to 0.16 km/s. The larger the meteoroid (i.e. asteroids and comets) the more of its initial cosmic velocity it preserves. While an object of 9,000 kg maintains about 6% of its original velocity, one of 900,000 kg already preserves about 70%. Extremely large bodies (about 100,000 tonnes) are not slowed by
670-457: 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
804-419: 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
938-435: 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
1072-498: 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
1206-463: 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
1340-510: 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
1474-455: A hole in the surface without filling in nearby craters. This may explain the 'sponge-like' appearance of that moon. It is convenient to divide the impact process conceptually into three distinct stages: (1) initial contact and compression, (2) excavation, (3) modification and collapse. In practice, there is overlap between the three processes with, for example, the excavation of the crater continuing in some regions while modification and collapse
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#17327986575151608-448: 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
1742-452: A large impact. The subsequent excavation of the crater occurs more slowly, and during this stage the flow of material is largely subsonic. During excavation, the crater grows as the accelerated target material moves away from the point of impact. The target's motion is initially downwards and outwards, but it becomes outwards and upwards. The flow initially produces an approximately hemispherical cavity that continues to grow, eventually producing
1876-474: 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
2010-558: A regular sequence with increasing size: small complex craters with a central topographic peak are called central peak craters, for example Tycho ; intermediate-sized craters, in which the central peak is replaced by a ring of peaks, are called peak-ring craters , for example Schrödinger ; and the largest craters contain multiple concentric topographic rings, and are called multi-ringed basins , for example Orientale . On icy (as opposed to rocky) bodies, other morphological forms appear that may have central pits rather than central peaks, and at
2144-409: A result, the impactor is compressed, its density rises, and the pressure within it increases dramatically. Peak pressures in large impacts exceed 1 T Pa to reach values more usually found deep in the interiors of planets, or generated artificially in nuclear explosions . In physical terms, a shock wave originates from the point of contact. As this shock wave expands, it decelerates and compresses
2278-625: A sample of articles of confirmed and well-documented impact sites. See the Earth Impact Database , a website concerned with 190 (as of July 2019 ) scientifically confirmed impact craters on Earth. There are approximately twelve more impact craters/basins larger than 300 km on the Moon, five on Mercury, and four on Mars. Large basins, some unnamed but mostly smaller than 300 km, can also be found on Saturn's moons Dione, Rhea and Iapetus. Hiroshima bomb Little Boy
2412-508: 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
2546-441: A significant crater volume may also be formed by the permanent compaction of the pore space . Such compaction craters may be important on many asteroids, comets and small moons. In large impacts, as well as material displaced and ejected to form the crater, significant volumes of target material may be melted and vaporized together with the original impactor. Some of this impact melt rock may be ejected, but most of it remains within
2680-574: 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 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
2814-406: A small angle, and high-temperature highly shocked material is expelled from the convergence zone with velocities that may be several times larger than the impact velocity. In most circumstances, the transient cavity is not stable and collapses under gravity. In small craters, less than about 4 km diameter on Earth, there is some limited collapse of the crater rim coupled with debris sliding down
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#17327986575152948-401: 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,
3082-451: 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
3216-537: A truck driver and model maker from Illinois who had studied every photograph and document on 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
3350-504: Is Peine , 35 km (22 mi) northeast of the crater. An old Inka road, which goes from the Pacific Ocean to San Pedro de Atacama and further to Argentina, runs 100–200 m (330–660 ft) from the crater. The crater has been deemed by Stanislav Kaniansky and Kristian Molnár to be one of the "most impressive" in the world and has a high scenic and historical value. The Chilean Geological Society has defined it as one of
3484-402: Is already underway in others. In the absence of atmosphere , the impact process begins when the impactor first touches the target surface. This contact accelerates the target and decelerates the impactor. Because the impactor is moving so rapidly, the rear of the object moves a significant distance during the short-but-finite time taken for the deceleration to propagate across the impactor. As
3618-512: Is ejected from close to the center of impact, and the slowest material is ejected close to the rim at low velocities to form an overturned coherent flap of ejecta immediately outside the rim. As ejecta escapes from the growing crater, it forms an expanding curtain in the shape of an inverted cone. The trajectory of individual particles within the curtain is thought to be largely ballistic. Small volumes of un-melted and relatively un-shocked material may be spalled at very high relative velocities from
3752-459: Is estimated that the value of materials mined from impact structures is five billion dollars/year just for North America. The eventual usefulness of impact craters depends on several factors, especially the nature of the materials that were impacted and when the materials were affected. In some cases, the deposits were already in place and the impact brought them to the surface. These are called "progenetic economic deposits." Others were created during
3886-404: Is sufficient to melt the impactor, and in larger impacts to vaporize most of it and to melt large volumes of the target. As well as being heated, the target near the impact is accelerated by the shock wave, and it continues moving away from the impact behind the decaying shock wave. Contact, compression, decompression, and the passage of the shock wave all occur within a few tenths of a second for
4020-437: Is the largest goldfield in the world, which has supplied about 40% of all the gold ever mined in an impact structure (though the gold did not come from the bolide). The asteroid that struck the region was 9.7 km (6 mi) wide. The Sudbury Basin was caused by an impacting body over 9.7 km (6 mi) in diameter. This basin is famous for its deposits of nickel , copper , and platinum group elements . An impact
4154-753: 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
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4288-518: 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
4422-477: 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
4556-829: 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
4690-497: The Nevada Test Site , notably Jangle U in 1951 and Teapot Ess in 1955. In 1960, Edward C. T. Chao and Shoemaker identified coesite (a form of silicon dioxide ) at Meteor Crater, proving the crater was formed from an impact generating extremely high temperatures and pressures. They followed this discovery with the identification of coesite within suevite at Nördlinger Ries , proving its impact origin. Armed with
4824-460: 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
4958-498: 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
5092-486: The geosites of Chile, although such a classification has no legal effect and the crater is threatened by erosion caused by vehicles and the over-collection of rocks. In 2017, several Chilean organizations and the community of Peine petitioned the Chilean government to declare the site a historic monument . Monturaqui crater is a tourist attraction in the area, which has led to the removal of meteoritic rocks and damage to
5226-455: 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
5360-503: 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
5494-452: The salt pan deposits and it could be considered a "salt pan oasis ". The dry climate (the annual precipitation is less than 1 mm (0.039 in)) means that water in the crater tends to evaporate. A magnetic anomaly is associated with the crater. It is located at about 3,015 m (9,892 ft) elevation. The terrain in the area consists of Paleozoic granites that are covered by Pliocene ignimbrites , and slopes northward to
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5628-429: The speed of sound in those objects. Such hyper-velocity impacts produce physical effects such as melting and vaporization that do not occur in familiar sub-sonic collisions. On Earth, ignoring the slowing effects of travel through the atmosphere, the lowest impact velocity with an object from space is equal to the gravitational escape velocity of about 11 km/s. The fastest impacts occur at about 72 km/s in
5762-399: The stable interior regions of continents . Few undersea craters have been discovered because of the difficulty of surveying the sea floor, the rapid rate of change of the ocean bottom, and the subduction of the ocean floor into Earth's interior by processes of plate tectonics . Daniel M. Barringer, a mining engineer, was convinced already in 1903 that the crater he owned, Meteor Crater ,
5896-424: 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 the fission of the uranium. Its lethal radius was approximately 1.3 kilometers (0.8 mi), covering about half of
6030-592: 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
6164-493: The "worst case" scenario in which an object in a retrograde near-parabolic orbit hits Earth. The median impact velocity on Earth is about 20 km/s. However, the slowing effects of travel through the atmosphere rapidly decelerate any potential impactor, especially in the lowest 12 kilometres where 90% of the Earth's atmospheric mass lies. Meteorites of up to 7,000 kg lose all their cosmic velocity due to atmospheric drag at
6298-457: 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 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
6432-616: 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 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
6566-581: 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. Although the casings, barrels, and components were tested, no enriched uranium
6700-621: 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 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
6834-565: The Salar de Atacama, thus explaining the tilt of the crater. Dykes cut through the granitic units, and both ignimbrites and granites are faulted . The impact primarily affected the granitic units but both units are apparent in the crater walls and the ignimbrites cover the rim crest. The impact has been dated with radiometric dating to have occurred about 663,000 ± 28,000 years ago. Various surface exposure dating techniques yield ages of about 500,000–780,000 years. Since then, erosion has altered
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#17327986575156968-478: The actual impact. The great energy involved caused melting. Useful minerals formed as a result of this energy are classified as "syngenetic deposits." The third type, called "epigenetic deposits," is caused by the creation of a basin from the impact. Many of the minerals that our modern lives depend on are associated with impacts in the past. The Vredeford Dome in the center of the Witwatersrand Basin
7102-469: The association of volcanic flows and other volcanic materials. Impact craters produce melted rocks as well, but usually in smaller volumes with different characteristics. The distinctive mark of an impact crater is the presence of rock that has undergone shock-metamorphic effects, such as shatter cones , melted rocks, and crystal deformations. The problem is that these materials tend to be deeply buried, at least for simple craters. They tend to be revealed in
7236-432: The atmosphere at all, and impact with their initial cosmic velocity if no prior disintegration occurs. Impacts at these high speeds produce shock waves in solid materials, and both impactor and the material impacted are rapidly compressed to high density. Following initial compression, the high-density, over-compressed region rapidly depressurizes, exploding violently, to set in train the sequence of events that produces
7370-489: 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
7504-436: 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
7638-560: 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
7772-417: 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
7906-415: 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 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
8040-471: 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
8174-451: The collapse and modification of the transient cavity is much more extensive, and the resulting structure is called a complex crater . The collapse of the transient cavity is driven by gravity, and involves both the uplift of the central region and the inward collapse of the rim. The central uplift is not the result of elastic rebound, which is a process in which a material with elastic strength attempts to return to its original geometry; rather
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#17327986575158308-468: The collapse is a process in which a material with little or no strength attempts to return to a state of gravitational equilibrium . Complex craters have uplifted centers, and they have typically broad flat shallow crater floors, and terraced walls . At the largest sizes, one or more exterior or interior rings may appear, and the structure may be labeled an impact basin rather than an impact crater. Complex-crater morphology on rocky planets appears to follow
8442-527: 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
8576-643: The crater by depositing fluvial and mass wasting deposits in it, gullying its sides and by lowering the rim. Originally, the Monturaqui crater was connected with the Campo del Cielo or the Rio Cuarto impact structures in Argentina. The meteorite probably hit from the northwest at an angle of 41° and was travelling at a velocity of about 15 km/s (9.3 mi/s). Because of the elevation at which it hit
8710-451: The crater walls and drainage of impact melts into the deeper cavity. The resultant structure is called a simple crater, and it remains bowl-shaped and superficially similar to the transient crater. In simple craters, the original excavation cavity is overlain by a lens of collapse breccia , ejecta and melt rock, and a portion of the central crater floor may sometimes be flat. Above a certain threshold size, which varies with planetary gravity,
8844-583: The crater. Monturaqui lies in a remote region of the Atacama Desert south of the Salar de Atacama , in the " precordillera ". The city of Antofagasta lies 200 km (120 mi) northwest of the crater. Administratively, the crater is in the Antofagasta Region . Monturaqui is a nearly circular, well-preserved 350 m × 370 m (1,150 ft × 1,210 ft) wide and 34 m (112 ft) deep impact crater . It has
8978-405: The craters on the Moon as logical impact sites that were formed not gradually, in eons , but explosively, in seconds." For his PhD degree at Princeton University (1960), under the guidance of Harry Hammond Hess , Shoemaker studied the impact dynamics of Meteor Crater. Shoemaker noted that Meteor Crater had the same form and structure as two explosion craters created from atomic bomb tests at
9112-496: 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
9246-425: 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, the distance of these effects scale as a function of the yield raised to an exponential power of 1 ⁄ 3 . So
9380-548: The dominant geographic features on many solid Solar System objects including the Moon , Mercury , Callisto , Ganymede , and most small moons and asteroids . On other planets and moons that experience more active surface geological processes, such as Earth , Venus , Europa , Io , Titan , and Triton , visible impact craters are less common because they become eroded , buried, or transformed by tectonic and volcanic processes over time. Where such processes have destroyed most of
9514-460: 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. 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
9648-407: The expanding vapor cloud may rise to many times the scale height of the atmosphere, effectively expanding into free space. Most material ejected from the crater is deposited within a few crater radii, but a small fraction may travel large distances at high velocity, and in large impacts it may exceed escape velocity and leave the impacted planet or moon entirely. The majority of the fastest material
9782-504: 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 a lifelong increase in cancer risk. To date, no radiation-related evidence of heritable diseases has been observed among
9916-502: 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"
10050-459: 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, 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
10184-401: The full depth of the transient cavity; typically the depth of maximum excavation is only about a third of the total depth. As a result, about one third of the volume of the transient crater is formed by the ejection of material, and the remaining two thirds is formed by the displacement of material downwards, outwards and upwards, to form the elevated rim. For impacts into highly porous materials,
10318-448: The geologists John D. Boon and Claude C. Albritton Jr. revisited Bucher's studies and concluded that the craters that he studied were probably formed by impacts. Grove Karl Gilbert suggested in 1893 that the Moon's craters were formed by large asteroid impacts. Ralph Baldwin in 1949 wrote that the Moon's craters were mostly of impact origin. Around 1960, Gene Shoemaker revived the idea. According to David H. Levy , Shoemaker "saw
10452-415: The ground, the meteorite had traversed only a little more than half the atmosphere and thus had not lost as much mass as it would have had it hit ground at sea level. The impact heated the ground to temperatures exceeding 1,400 °C (2,550 °F), probably reaching 1,500–1,600 °C (2,730–2,910 °F), and had an energy comparable to that of 2.2 Hiroshima bombs . The formation of the crater disrupted
10586-478: 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 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
10720-430: The impact and others were turned to glass . Impact-generated rocks formed mostly from granite and meteorite material. They are mostly found at the east-southeast side of the crater, with lesser amounts on its inside. Only a few or no fragments of the meteorite have been recovered. Given the proximity of the crater to an old road, this may be due to traders and herdsmen removing meteorite fragments but it may also be due to
10854-599: The impact crater. Impact-crater formation is therefore more closely analogous to cratering by high explosives than by mechanical displacement. Indeed, the energy density of some material involved in the formation of impact craters is many times higher than that generated by high explosives. Since craters are caused by explosions , they are nearly always circular – only very low-angle impacts cause significantly elliptical craters. This describes impacts on solid surfaces. Impacts on porous surfaces, such as that of Hyperion , may produce internal compression without ejecta, punching
10988-521: The impactor, and it accelerates and compresses the target. Stress levels within the shock wave far exceed the strength of solid materials; consequently, both the impactor and the target close to the impact site are irreversibly damaged. Many crystalline minerals can be transformed into higher-density phases by shock waves; for example, the common mineral quartz can be transformed into the higher-pressure forms coesite and stishovite . Many other shock-related changes take place within both impactor and target as
11122-463: 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, a survey team from the Manhattan Project that included William Penney , Robert Serber, and George T. Reynolds
11256-764: The knowledge of shock-metamorphic features, Carlyle S. Beals and colleagues at the Dominion Astrophysical Observatory in Victoria, British Columbia , Canada and Wolf von Engelhardt of the University of Tübingen in Germany began a methodical search for impact craters. By 1970, they had tentatively identified more than 50. Although their work was controversial, the American Apollo Moon landings, which were in progress at
11390-649: The largest sizes may contain many concentric rings. Valhalla on Callisto is an example of this type. Long after an impact event, a crater may be further modified by erosion, mass wasting processes, viscous relaxation, or erased entirely. These effects are most prominent on geologically and meteorologically active bodies such as Earth, Titan, Triton, and Io. However, heavily modified craters may be found on more primordial bodies such as Callisto, where many ancient craters flatten into bright ghost craters, or palimpsests . Non-explosive volcanic craters can usually be distinguished from impact craters by their irregular shape and
11524-402: The local drainage network, which redeveloped to run around the crater. The impacting body was a metallic asteroid containing iron and nickel . It has been identified as a group I octahedrite and as an IAB meteorite with a size of about 15 m (49 ft). The impact has produced rocks such as impact glass , coesite and shocked quartz ; some rocks were completely melted during
11658-412: The material are more likely to get scattered in 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 ,
11792-406: The metals being oxidized over time. They include rocks called "iron shale", they are magnetic indicating their origin in the meteorite. The nonoxidized parts consist of cohenite , rabdite , schreibersite and taenite . Other minerals are goethite , lepidocrocite , maghemite , pentlandite and reevesite . Metallic spherules occur. Fragments of the Monturaqui meteorite have been collected in
11926-528: The meteorite collection of " Giorgio Abetti " Astronomical Observatory and Museum, San Giovanni in Persiceto, Bologna , Italy. Impact crater An impact crater is a depression in the surface of a solid astronomical body formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters , which result from explosion or internal collapse, impact craters typically have raised rims and floors that are lower in elevation than
12060-481: 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
12194-411: The original crater topography , the terms impact structure or astrobleme are more commonly used. In early literature, before the significance of impact cratering was widely recognised, the terms cryptoexplosion or cryptovolcanic structure were often used to describe what are now recognised as impact-related features on Earth. The cratering records of very old surfaces, such as Mercury, the Moon, and
12328-711: The outer Solar System could be different from the inner Solar System. Although Earth's active surface processes quickly destroy the impact record, about 190 terrestrial impact craters have been identified. These range in diameter from a few tens of meters up to about 300 km (190 mi), and they range in age from recent times (e.g. the Sikhote-Alin craters in Russia whose creation was witnessed in 1947) to more than two billion years, though most are less than 500 million years old because geological processes tend to obliterate older craters. They are also selectively found in
12462-420: The people inside the area where the shock wave carried such an overpressure or greater would be killed. At Hiroshima, that area 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
12596-479: The planet than have been discovered so far. The cratering rate in the inner solar system fluctuates as a consequence of collisions in the asteroid belt that create a family of fragments that are often sent cascading into the inner solar system. Formed in a collision 80 million years ago, the Baptistina family of asteroids is thought to have caused a large spike in the impact rate. The rate of impact cratering in
12730-514: 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 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
12864-510: 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 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
12998-425: 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
13132-463: 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
13266-405: 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
13400-491: 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), 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,
13534-410: 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 a single spherical nuclear explosion was largely wasted. A cluster bomb pattern of smaller explosions would have been a more energy-efficient match to
13668-554: 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
13802-464: 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 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
13936-425: The shape of a bowl and is elongated in northwest–southeast direction. The height of its rim ranges between 16–48 m (52–157 ft) with the southern rim being about 10–15 m (33–49 ft) higher than the northern. Sedimentation in rain-fed ponds has left a 40 m (430 sq ft) playa in the crater, which lies in its northeastern quadrant and is surrounded by lake sediments. Bushes grow close to
14070-419: The shock wave passes through, and some of these changes can be used as diagnostic tools to determine whether particular geological features were produced by impact cratering. As the shock wave decays, the shocked region decompresses towards more usual pressures and densities. The damage produced by the shock wave raises the temperature of the material. In all but the smallest impacts this increase in temperature
14204-464: The southern highlands of Mars, record a period of intense early bombardment in the inner Solar System around 3.9 billion years ago. The rate of crater production on Earth has since been considerably lower, but it is appreciable nonetheless. Earth experiences, on average, from one to three impacts large enough to produce a 20-kilometre-diameter (12 mi) crater every million years. This indicates that there should be far more relatively young craters on
14338-484: 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 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
14472-400: 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
14606-425: The surface of the target and from the rear of the impactor. Spalling provides a potential mechanism whereby material may be ejected into inter-planetary space largely undamaged, and whereby small volumes of the impactor may be preserved undamaged even in large impacts. Small volumes of high-speed material may also be generated early in the impact by jetting. This occurs when two surfaces converge rapidly and obliquely at
14740-507: The surrounding terrain. Impact craters are typically circular, though they can be elliptical in shape or even irregular due to events such as landslides. Impact craters range in size from microscopic craters seen on lunar rocks returned by the Apollo Program to simple bowl-shaped depressions and vast, complex, multi-ringed impact basins . Meteor Crater is a well-known example of a small impact crater on Earth. Impact craters are
14874-518: 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 the Atomic Bomb Casualty Commission in 1946, a joint U.S.–Japanese project to track radiation injuries among survivors. In 1975 its work
15008-521: 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 the prospect of no more plutonium for new cores and no more polonium for the initiators for the cores that had already been produced,
15142-399: 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
15276-473: The time, provided supportive evidence by recognizing the rate of impact cratering on the Moon . Because the processes of erosion on the Moon are minimal, craters persist. Since the Earth could be expected to have roughly the same cratering rate as the Moon, it became clear that the Earth had suffered far more impacts than could be seen by counting evident craters. Impact cratering involves high velocity collisions between solid objects, typically much greater than
15410-411: The transient crater, initially forming a layer of impact melt coating the interior of the transient cavity. In contrast, the hot dense vaporized material expands rapidly out of the growing cavity, carrying some solid and molten material within it as it does so. As this hot vapor cloud expands, it rises and cools much like the archetypal mushroom cloud generated by large nuclear explosions. In large impacts,
15544-413: The tungsten carbide tamper , it must be 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
15678-403: The uplifted center of a complex crater, however. Impacts produce distinctive shock-metamorphic effects that allow impact sites to be distinctively identified. Such shock-metamorphic effects can include: On Earth, impact craters have resulted in useful minerals. Some of the ores produced from impact related effects on Earth include ores of iron , uranium , gold , copper , and nickel . It
15812-405: 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
15946-471: 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
16080-490: 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
16214-531: 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 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,
16348-481: 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, the best value for the Nagasaki bomb was evaluated as 21 kilotons of TNT (88 TJ) with an uncertainty of 10% (±2 kt),
16482-606: 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
16616-471: 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
16750-457: Was discovered in 1962 and identified as an impact crater in 1966. The crater was first suspected to be an impact crater in 1962, when it was found on aerial images. After geologic research on the site found evidence of the impact event, it was identified as an impact crater in 1966. The crater has not been drilled. Its name is derived from the mountain range where it is located and from the town of Monturaqui 70 km (43 mi). The closest town
16884-449: 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
17018-684: Was involved in making the Carswell structure in Saskatchewan , Canada; it contains uranium deposits. Hydrocarbons are common around impact structures. Fifty percent of impact structures in North America in hydrocarbon-bearing sedimentary basins contain oil/gas fields. On Earth, the recognition of impact craters is a branch of geology, and is related to planetary geology in the study of other worlds. Out of many proposed craters, relatively few are confirmed. The following twenty are
17152-463: Was of cosmic origin. Most geologists at the time assumed it formed as the result of a volcanic steam eruption. In the 1920s, the American geologist Walter H. Bucher studied a number of sites now recognized as impact craters in the United States. He concluded they had been created by some great explosive event, but believed that this force was probably volcanic in origin. However, in 1936,
17286-479: 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 the fire, and broken water pipes rendered hydrants useless. At Nagasaki, the fires failed to merge into
17420-470: 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
17554-486: 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 the Project Ichiban data, and the pressure-wave data from The Great Artiste ,
17688-514: 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 the relationship between radiation exposure and later health outcomes. But it failed to clear up all
17822-558: 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 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
17956-455: 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
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