Information AboutLittle Boy |
| CATEGORIES ABOUT LITTLE BOY | |
| nuclear bombs | |
| manhattan project | |
| atomic bombings of hiroshima and nagasaki | |
| gun-type nuclear bombs | |
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Little Boy was the Codename of the Atomic Bomb which was dropped on Hiroshima , on August 6 , 1945 by the 12-man crew of the B-29 Superfortress '' Enola Gay '', piloted by Lieutenant Colonel Paul Tibbets of the United States Army Air Forces . It was the first atomic bomb ever used as an offensive weapon and came three days before the dropping of " Fat Man " on Nagasaki . The weapon was developed during the Manhattan Project ( World War II ), and derived its explosive power from the Nuclear Fission ing of Enriched Uranium . The Hiroshima Bombing was the second Nuclear Explosion in history (the first was the "Trinity" Test ). BASIC WEAPON DESIGN See Also: Gun-type fission weapon Nuclear weapon design The Mk I "Little Boy" was 10 feet (3 m) in length, 28 inches (71 cm) wide and weighed 8,900 lb (4000 kg). The design used the Gun Method to explosively force a sub- Critical Mass of Uranium -235 and three U-235 target rings together into a super-critical mass, initiating a Nuclear Chain Reaction . This was accomplished by simply shooting one piece of the uranium into the other by means of chemical explosives. It contained 60 kg U-235, of which 0.7 kg underwent Nuclear Fission . No full test of a gun-type nuclear weapon had occurred before the "Little Boy" device was dropped over Hiroshima . The only Test Explosion of a nuclear weapon had been of an implosion-type weapon utilizing Plutonium as its fissionable material, on July 16 , 1945 at the Trinity Test . There were a number of reasons for not testing the "Little Boy" device. A primary one was the fact that there was a very scarce amount of uranium-235 compared with the relatively large amount of plutonium which was expected to be able to be produced monthly from the Hanford reactors. Additionally, the weapon design was simple enough in concept that it was deemed only necessary to conduct limited testing of the gun-type assembly (known during the war as "tickling the dragon's tail"). Unlike the implosion design, which requires very sophisticated coordination of shaped explosive charges, the gun-type design was considered almost guaranteed to work without full testing. Although used occasionally in later experimental devices, the design was used only once as a weapon because of the extreme danger of a misfire. A simple crash could drive the "bullet" into the "target" and release lethal radiation doses or even a full nuclear detonation. The danger of misfire was even greater over water. Even if the force of a crash did not set the bomb off, if water entered the fail safe system, it would be shorted out, possibly leading to a detonation of the bomb. The British Red Beard nuclear weapon also suffered from this flaw. None of the other five Mark I bombs built on the model of Little Boy were used by the US Army. ASSEMBLY DETAILS The exact specifications of the "Little Boy" bomb have never been declassified for security reasons, though many sources have speculated and relied upon limited photographic evidence to reconstruct its internal dimensions. In the weapon, the uranium-235 material was divided into two parts, following the gun principle: the "projectile" and the "target". The "projectile" was a cylinder, about 16 cm long and 10 cm wide, with 40% of the total mass (25.6 kg). It was a pile of 6 uranium rings protected by a casing of steel, with a tungsten carbide and steel backing plate at the back end. The whole thing was locked in a 2 mm thick steel box. The "target" was a hollowed-out cylinder, 16 cm long and in diameter, with a 10 cm diameter hole in the middle for the bullet, with a Uranium mass of 38.4 kg. The most enriched uranium was probably placed in the projectile to increase the yield of the explosion. The two parts were protected by Boron casings designed to absorb the neutrons, one inside the target and one surrounding the projectile (described as a Sabot ). When the projectile reached the target, the boron protection was supposed to be removed; the segment inside the target pushed forwards into a cavity at the nose, and the sabot around the projectile stripped off just as it reached the target assembly. The system of neutron reflectors was composed of steel and tungsten. This part, called the ''tamper'', weighted 2.3 tonnes. The "target" was to lodge itself in this part. The tube of the gun was 10 cm wide and about 180 cm long, and weighted 450 kg. To launch the uranium at a speed of 300 m/s, Cordite was used, an artillery explosive based on Nitrocellulose and Nitroglycerine . |
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