Information AboutFat Man |
| CATEGORIES ABOUT FAT MAN | |
| manhattan project | |
| nuclear bombs | |
| atomic bombings of hiroshima and nagasaki | |
| american cold war nuclear bombs | |
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"Fat-Man" was the codename of the Atomic Bomb which was detonated over Nagasaki , Japan by the United States , on August 9 , 1945 . It was the second of the two nuclear weapons to be used in Warfare . The name also refers more generically to the early Nuclear Weapon Design s of U.S. weapons based on the "Fat Man" model. TECHNOLOGY The weapon was 7 feet 8 inches (2.34 m) long, five feet (1.52 m) in diameter, and weighed 10,200 pounds (4,630 Kg ). In accordance with the name, it was more than twice as wide as Little Boy , dropped on Hiroshima three days earlier; however, the mass was only 10% more. It was detonated at an altitude of about 1,800 feet (550 m) over the city. It was dropped from the from Nuclear Fallout . "Fat Man" was an Implosion type weapon using Plutonium . A subcritical sphere of plutonium was placed in the center of a hollow sphere of High Explosive . Numerous Detonators located on the surface of the high explosive were fired simultaneously to produce a powerful inward Pressure on the core, squeezing it and increasing its density, resulting in a supercritical condition and a nuclear explosion. At first it was thought that two pieces of sub-critical plutonium (Pu-239) could simply be shot into one another to create a nuclear explosion, and a plutonium gun-type design of this sort (known as the " Thin Man " bomb) was worked on for some time during the Manhattan Project. However in April 1944 it was discovered that plutonium created for the bomb in the Nuclear Reactor s at Hanford, Washington , even though it was super-grade weapon plutonium containing only about 0.9% Pu-240, was not as pure as the initial samples of plutonium developed at the Cyclotron s at Ernest O. Lawrence 's Radiation Laboratory in Berkeley, California . Because of the presence of the isotope Pu-240, reactor-bred plutonium had a much higher rate of spontaneous Neutron Emission than was previously thought, and if a gun-type device was used it would most likely pre-detonate and result in a messy and costly "fizzle". The Spontaneous Fission rate of Pu-240 is 415,000 fissions/(s·kg), and the amount was 0.9% of 6.2 kg, is 56 g. Thus there were 23,000 spontaneous fissions per second. This means that the last few centimeters would have to be travelled in preferably much less than 40 microseconds. It is theoretically possible to build a plutonium gun-type device, but it would need to be 19 feet long in order to allow the sub-critical masses to be fused into a critical mass before a fizzle occurs. The mass of a plutonium gun-type device would have been beyond the payload of the B-29. After this problem was realized in, the entire Los Alamos laboratory re-organized around the problem of the implosion bomb, the "Fat Man" starting in June 1944. The gun-type method could still be used for highly-enriched Uranium , though, and was employed in the " Little Boy " weapon which was used against Hiroshima , Japan . For a variety of reasons, the implosion method is both more efficient than the gun-type method, and also far safer, as a perfect synchronization of the explosion lenses is required for the core to properly detonate, greatly reducing the chances of an accidental nuclear detonation. " device was similar to the "Fat Man" bomb.]] Because of its complicated firing mechanism, and the need for previously untested synchronization of explosives and precision design, it was felt that a full test of the concept was needed before the scientists and military representatives could be confident it would perform correctly under combat conditions. On July 16 , 1945 , a device utilizing a similar mechanism (called the " Gadget " for security reasons) detonated in a Test Explosion at a remote site in New Mexico , known as the " Trinity " test. In the end, it gave somewhere around 20 kt (80 TJ), 2 to 4 times the expected yield. The Soviet Union's First Nuclear Weapon detonated at Operation First Lightning (known as " Joe 1 " in the West) was more or less a purposeful copy of the "Fat Man" device, on which they had obtained detailed information from the spy Klaus Fuchs . THE BOMBING '' and a replica of ''Fat Man'' on display at the National Museum Of The United States Air Force ]] "Fat Man" and "Little Boy" were flown from the United States controlled island of Tinian in the Northern Mariana Islands, to where they would eventually rest in Japan. Immediately after the bombings of Japan, the United States produced a technical history of the Manhattan Project, known as the Smyth Report , that did not disclose the information that the "Fat Man" device was different from the "Little Boy" device, and did not imply that a different method was required for plutonium weapons. The "implosion" design was considered top-secret in the United States until it was declassified and released during the testimony of David Greenglass against Ethel And Julius Rosenberg in 1951 . Photographs of the casings of "Little Boy" and "Fat Man" were not released publicly until the 1960s. The United States produced a small stockpile of "Fat Man" bombs after the war, but they were highly idiosyncratic and extremely delicate. It was eventually re-worked in the MK 4 Fat Man bomb, which was similar in principle but was appropriate for long-term stockpiling, use by non-experts, and used a more efficient implosion system (with a 60 point implosion system, compared to the 32 point weapon used in the war). THE GADGET Schematic cross-section of the "gadget"; some boundaries are approximate. From left to right (outside inward):
INTERIOR OF BOMB The original blueprints of the interior of both Fat Man and Little Boy are still classified. However, there is much information about the main parts. SEE ALSO
EXTERNAL LINKS
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